Re: [PATCH 01/44] drivers/base: Always release devres on device_del
On Fri, May 15, 2020 at 02:55:38PM +0200, Greg Kroah-Hartman wrote: > On Tue, Apr 28, 2020 at 03:15:12PM +0200, Daniel Vetter wrote: > > On Mon, Apr 06, 2020 at 03:55:28PM +0200, Daniel Vetter wrote: > > > On Mon, Apr 6, 2020 at 3:38 PM Greg Kroah-Hartman > > > wrote: > > > > > > > > On Mon, Apr 06, 2020 at 02:32:51PM +0200, Daniel Vetter wrote: > > > > > On Fri, Apr 3, 2020 at 3:58 PM Daniel Vetter > > > > > wrote: > > > > > > > > > > > > In drm we've added nice drm_device (the main gpu driver thing, which > > > > > > also represents the userspace interfaces and has everything else > > > > > > dangling off it) init functions using devres, devm_drm_dev_init and > > > > > > soon devm_drm_dev_alloc (this patch series adds that). > > > > > > > > > > > > A slight trouble is that drm_device itself holds a reference on the > > > > > > struct device it's sitting on top (for sysfs links and dmesg debug > > > > > > and > > > > > > lots of other things), so there's a reference loop. For real drivers > > > > > > this is broken at remove/unplug time, where all devres resources are > > > > > > released device_release_driver(), before the final device reference > > > > > > is > > > > > > dropped. So far so good. > > > > > > > > > > > > There's 2 exceptions: > > > > > > - drm/vkms|vgem: Virtual drivers for which we create a fake/virtual > > > > > > platform device to make them look more like normal devices to > > > > > > userspace. These aren't drivers in the driver model sense, we > > > > > > simple > > > > > > create a platform_device and register it. > > > > > > > > > > > > - drm/i915/selftests, where we create minimal mock devices, and > > > > > > again > > > > > > the selftests aren't proper drivers in the driver model sense. > > > > > > > > > > > > For these two cases the reference loop isn't broken, because devres > > > > > > is > > > > > > only cleaned up when the last device reference is dropped. But > > > > > > that's > > > > > > not happening, because the drm_device holds that last struct device > > > > > > reference. > > > > > > > > > > > > Thus far this wasn't a problem since the above cases simply > > > > > > hand-rolled their cleanup code. But I want to convert all drivers > > > > > > over > > > > > > to the devm_ versions, hence it would be really nice if these > > > > > > virtual/fake/mock uses-cases could also be managed with devres > > > > > > cleanup. > > > > > > > > > > > > I see three possible approaches: > > > > > > > > > > Restarting this at the top level, because the discussion thus far just > > > > > ended in a long "you're doing it wrong", despite that I think we're > > > > > doing what v4l is doing (plus/minus that we can't do an exact matching > > > > > handling in drm because our uapi has a lot more warts, which we can't > > > > > change because no breaking userspace). > > > > > > > > > > So which one of the three below is the right approach? > > > > > > > > > > Aside, looking at the v4l solution I think there's also a confusion > > > > > about struct device representing a char device (which v4l directly > > > > > uses as its userspace interface refcounted thing, and which drm does > > > > > _not_ directly). And a struct device embedded into something like > > > > > platform_device or a virtual device, where a driver can bind to. My > > > > > question here is about the former, I don't care how cdev struct device > > > > > are cleaned up one bit. Now if other subsystems relies on the devres > > > > > cleanup behaviour we currently have because of such cdev usage, then > > > > > yeah first approach doesn't work (and I have a big surprised that use > > > > > case, but hey would actually learn something). > > > > > > > > > > End of aside, since again I want to figure out which of the tree > > > > > approaches it the right one. Not about how wrong one of them is, > > > > > ignoring the other three I laid out. And maybe there's even more > > > > > options for this. > > > > > > > > Sorry, been swamped with other things, give me a few days to get back to > > > > this, I need to dig into how you all are dealing with the virtual > > > > drivers. > > > > > > Sure, no problem. > > > > > > > Doing this in the middle of the merge window is a bit rough :) > > > > > > Ah I always forget ... we freeze drm at -rc6, so merge window is > > > actually my most relaxed time since everyone is busy and no one has > > > time to report drm bugs :-) > > > > Hi Greg, > > > > Since -rc3 is out, had any to ponder this? Otherwise we'll be right back > > in the next merge window ... > > I owe you a response to this. I'm going to try to carve out some time > on Monday to do this, sorry for the delay :( No worries, I got myself plenty occupied with other fun stuff in graphics for now. And the part of the series which doesn't need this here is all landed, so new drivers already look a notch cleaner in their code. I'd have poked you earlier, but ofc very much appreciated if you can look into this a bi
Re: [PATCH 01/44] drivers/base: Always release devres on device_del
On Tue, Apr 28, 2020 at 03:15:12PM +0200, Daniel Vetter wrote: > On Mon, Apr 06, 2020 at 03:55:28PM +0200, Daniel Vetter wrote: > > On Mon, Apr 6, 2020 at 3:38 PM Greg Kroah-Hartman > > wrote: > > > > > > On Mon, Apr 06, 2020 at 02:32:51PM +0200, Daniel Vetter wrote: > > > > On Fri, Apr 3, 2020 at 3:58 PM Daniel Vetter > > > > wrote: > > > > > > > > > > In drm we've added nice drm_device (the main gpu driver thing, which > > > > > also represents the userspace interfaces and has everything else > > > > > dangling off it) init functions using devres, devm_drm_dev_init and > > > > > soon devm_drm_dev_alloc (this patch series adds that). > > > > > > > > > > A slight trouble is that drm_device itself holds a reference on the > > > > > struct device it's sitting on top (for sysfs links and dmesg debug and > > > > > lots of other things), so there's a reference loop. For real drivers > > > > > this is broken at remove/unplug time, where all devres resources are > > > > > released device_release_driver(), before the final device reference is > > > > > dropped. So far so good. > > > > > > > > > > There's 2 exceptions: > > > > > - drm/vkms|vgem: Virtual drivers for which we create a fake/virtual > > > > > platform device to make them look more like normal devices to > > > > > userspace. These aren't drivers in the driver model sense, we simple > > > > > create a platform_device and register it. > > > > > > > > > > - drm/i915/selftests, where we create minimal mock devices, and again > > > > > the selftests aren't proper drivers in the driver model sense. > > > > > > > > > > For these two cases the reference loop isn't broken, because devres is > > > > > only cleaned up when the last device reference is dropped. But that's > > > > > not happening, because the drm_device holds that last struct device > > > > > reference. > > > > > > > > > > Thus far this wasn't a problem since the above cases simply > > > > > hand-rolled their cleanup code. But I want to convert all drivers over > > > > > to the devm_ versions, hence it would be really nice if these > > > > > virtual/fake/mock uses-cases could also be managed with devres > > > > > cleanup. > > > > > > > > > > I see three possible approaches: > > > > > > > > Restarting this at the top level, because the discussion thus far just > > > > ended in a long "you're doing it wrong", despite that I think we're > > > > doing what v4l is doing (plus/minus that we can't do an exact matching > > > > handling in drm because our uapi has a lot more warts, which we can't > > > > change because no breaking userspace). > > > > > > > > So which one of the three below is the right approach? > > > > > > > > Aside, looking at the v4l solution I think there's also a confusion > > > > about struct device representing a char device (which v4l directly > > > > uses as its userspace interface refcounted thing, and which drm does > > > > _not_ directly). And a struct device embedded into something like > > > > platform_device or a virtual device, where a driver can bind to. My > > > > question here is about the former, I don't care how cdev struct device > > > > are cleaned up one bit. Now if other subsystems relies on the devres > > > > cleanup behaviour we currently have because of such cdev usage, then > > > > yeah first approach doesn't work (and I have a big surprised that use > > > > case, but hey would actually learn something). > > > > > > > > End of aside, since again I want to figure out which of the tree > > > > approaches it the right one. Not about how wrong one of them is, > > > > ignoring the other three I laid out. And maybe there's even more > > > > options for this. > > > > > > Sorry, been swamped with other things, give me a few days to get back to > > > this, I need to dig into how you all are dealing with the virtual > > > drivers. > > > > Sure, no problem. > > > > > Doing this in the middle of the merge window is a bit rough :) > > > > Ah I always forget ... we freeze drm at -rc6, so merge window is > > actually my most relaxed time since everyone is busy and no one has > > time to report drm bugs :-) > > Hi Greg, > > Since -rc3 is out, had any to ponder this? Otherwise we'll be right back > in the next merge window ... I owe you a response to this. I'm going to try to carve out some time on Monday to do this, sorry for the delay :( greg k-h ___ dri-devel mailing list dri-devel@lists.freedesktop.org https://lists.freedesktop.org/mailman/listinfo/dri-devel
Re: [PATCH 01/44] drivers/base: Always release devres on device_del
On Mon, Apr 06, 2020 at 03:55:28PM +0200, Daniel Vetter wrote: > On Mon, Apr 6, 2020 at 3:38 PM Greg Kroah-Hartman > wrote: > > > > On Mon, Apr 06, 2020 at 02:32:51PM +0200, Daniel Vetter wrote: > > > On Fri, Apr 3, 2020 at 3:58 PM Daniel Vetter > > > wrote: > > > > > > > > In drm we've added nice drm_device (the main gpu driver thing, which > > > > also represents the userspace interfaces and has everything else > > > > dangling off it) init functions using devres, devm_drm_dev_init and > > > > soon devm_drm_dev_alloc (this patch series adds that). > > > > > > > > A slight trouble is that drm_device itself holds a reference on the > > > > struct device it's sitting on top (for sysfs links and dmesg debug and > > > > lots of other things), so there's a reference loop. For real drivers > > > > this is broken at remove/unplug time, where all devres resources are > > > > released device_release_driver(), before the final device reference is > > > > dropped. So far so good. > > > > > > > > There's 2 exceptions: > > > > - drm/vkms|vgem: Virtual drivers for which we create a fake/virtual > > > > platform device to make them look more like normal devices to > > > > userspace. These aren't drivers in the driver model sense, we simple > > > > create a platform_device and register it. > > > > > > > > - drm/i915/selftests, where we create minimal mock devices, and again > > > > the selftests aren't proper drivers in the driver model sense. > > > > > > > > For these two cases the reference loop isn't broken, because devres is > > > > only cleaned up when the last device reference is dropped. But that's > > > > not happening, because the drm_device holds that last struct device > > > > reference. > > > > > > > > Thus far this wasn't a problem since the above cases simply > > > > hand-rolled their cleanup code. But I want to convert all drivers over > > > > to the devm_ versions, hence it would be really nice if these > > > > virtual/fake/mock uses-cases could also be managed with devres > > > > cleanup. > > > > > > > > I see three possible approaches: > > > > > > Restarting this at the top level, because the discussion thus far just > > > ended in a long "you're doing it wrong", despite that I think we're > > > doing what v4l is doing (plus/minus that we can't do an exact matching > > > handling in drm because our uapi has a lot more warts, which we can't > > > change because no breaking userspace). > > > > > > So which one of the three below is the right approach? > > > > > > Aside, looking at the v4l solution I think there's also a confusion > > > about struct device representing a char device (which v4l directly > > > uses as its userspace interface refcounted thing, and which drm does > > > _not_ directly). And a struct device embedded into something like > > > platform_device or a virtual device, where a driver can bind to. My > > > question here is about the former, I don't care how cdev struct device > > > are cleaned up one bit. Now if other subsystems relies on the devres > > > cleanup behaviour we currently have because of such cdev usage, then > > > yeah first approach doesn't work (and I have a big surprised that use > > > case, but hey would actually learn something). > > > > > > End of aside, since again I want to figure out which of the tree > > > approaches it the right one. Not about how wrong one of them is, > > > ignoring the other three I laid out. And maybe there's even more > > > options for this. > > > > Sorry, been swamped with other things, give me a few days to get back to > > this, I need to dig into how you all are dealing with the virtual > > drivers. > > Sure, no problem. > > > Doing this in the middle of the merge window is a bit rough :) > > Ah I always forget ... we freeze drm at -rc6, so merge window is > actually my most relaxed time since everyone is busy and no one has > time to report drm bugs :-) Hi Greg, Since -rc3 is out, had any to ponder this? Otherwise we'll be right back in the next merge window ... Cheers, Daniel -- Daniel Vetter Software Engineer, Intel Corporation http://blog.ffwll.ch ___ dri-devel mailing list dri-devel@lists.freedesktop.org https://lists.freedesktop.org/mailman/listinfo/dri-devel
Re: [PATCH 01/44] drivers/base: Always release devres on device_del
On Mon, Apr 6, 2020 at 3:38 PM Greg Kroah-Hartman wrote: > > On Mon, Apr 06, 2020 at 02:32:51PM +0200, Daniel Vetter wrote: > > On Fri, Apr 3, 2020 at 3:58 PM Daniel Vetter wrote: > > > > > > In drm we've added nice drm_device (the main gpu driver thing, which > > > also represents the userspace interfaces and has everything else > > > dangling off it) init functions using devres, devm_drm_dev_init and > > > soon devm_drm_dev_alloc (this patch series adds that). > > > > > > A slight trouble is that drm_device itself holds a reference on the > > > struct device it's sitting on top (for sysfs links and dmesg debug and > > > lots of other things), so there's a reference loop. For real drivers > > > this is broken at remove/unplug time, where all devres resources are > > > released device_release_driver(), before the final device reference is > > > dropped. So far so good. > > > > > > There's 2 exceptions: > > > - drm/vkms|vgem: Virtual drivers for which we create a fake/virtual > > > platform device to make them look more like normal devices to > > > userspace. These aren't drivers in the driver model sense, we simple > > > create a platform_device and register it. > > > > > > - drm/i915/selftests, where we create minimal mock devices, and again > > > the selftests aren't proper drivers in the driver model sense. > > > > > > For these two cases the reference loop isn't broken, because devres is > > > only cleaned up when the last device reference is dropped. But that's > > > not happening, because the drm_device holds that last struct device > > > reference. > > > > > > Thus far this wasn't a problem since the above cases simply > > > hand-rolled their cleanup code. But I want to convert all drivers over > > > to the devm_ versions, hence it would be really nice if these > > > virtual/fake/mock uses-cases could also be managed with devres > > > cleanup. > > > > > > I see three possible approaches: > > > > Restarting this at the top level, because the discussion thus far just > > ended in a long "you're doing it wrong", despite that I think we're > > doing what v4l is doing (plus/minus that we can't do an exact matching > > handling in drm because our uapi has a lot more warts, which we can't > > change because no breaking userspace). > > > > So which one of the three below is the right approach? > > > > Aside, looking at the v4l solution I think there's also a confusion > > about struct device representing a char device (which v4l directly > > uses as its userspace interface refcounted thing, and which drm does > > _not_ directly). And a struct device embedded into something like > > platform_device or a virtual device, where a driver can bind to. My > > question here is about the former, I don't care how cdev struct device > > are cleaned up one bit. Now if other subsystems relies on the devres > > cleanup behaviour we currently have because of such cdev usage, then > > yeah first approach doesn't work (and I have a big surprised that use > > case, but hey would actually learn something). > > > > End of aside, since again I want to figure out which of the tree > > approaches it the right one. Not about how wrong one of them is, > > ignoring the other three I laid out. And maybe there's even more > > options for this. > > Sorry, been swamped with other things, give me a few days to get back to > this, I need to dig into how you all are dealing with the virtual > drivers. Sure, no problem. > Doing this in the middle of the merge window is a bit rough :) Ah I always forget ... we freeze drm at -rc6, so merge window is actually my most relaxed time since everyone is busy and no one has time to report drm bugs :-) Thanks, Daniel -- Daniel Vetter Software Engineer, Intel Corporation +41 (0) 79 365 57 48 - http://blog.ffwll.ch ___ dri-devel mailing list dri-devel@lists.freedesktop.org https://lists.freedesktop.org/mailman/listinfo/dri-devel
Re: [PATCH 01/44] drivers/base: Always release devres on device_del
On Mon, Apr 06, 2020 at 02:32:51PM +0200, Daniel Vetter wrote: > On Fri, Apr 3, 2020 at 3:58 PM Daniel Vetter wrote: > > > > In drm we've added nice drm_device (the main gpu driver thing, which > > also represents the userspace interfaces and has everything else > > dangling off it) init functions using devres, devm_drm_dev_init and > > soon devm_drm_dev_alloc (this patch series adds that). > > > > A slight trouble is that drm_device itself holds a reference on the > > struct device it's sitting on top (for sysfs links and dmesg debug and > > lots of other things), so there's a reference loop. For real drivers > > this is broken at remove/unplug time, where all devres resources are > > released device_release_driver(), before the final device reference is > > dropped. So far so good. > > > > There's 2 exceptions: > > - drm/vkms|vgem: Virtual drivers for which we create a fake/virtual > > platform device to make them look more like normal devices to > > userspace. These aren't drivers in the driver model sense, we simple > > create a platform_device and register it. > > > > - drm/i915/selftests, where we create minimal mock devices, and again > > the selftests aren't proper drivers in the driver model sense. > > > > For these two cases the reference loop isn't broken, because devres is > > only cleaned up when the last device reference is dropped. But that's > > not happening, because the drm_device holds that last struct device > > reference. > > > > Thus far this wasn't a problem since the above cases simply > > hand-rolled their cleanup code. But I want to convert all drivers over > > to the devm_ versions, hence it would be really nice if these > > virtual/fake/mock uses-cases could also be managed with devres > > cleanup. > > > > I see three possible approaches: > > Restarting this at the top level, because the discussion thus far just > ended in a long "you're doing it wrong", despite that I think we're > doing what v4l is doing (plus/minus that we can't do an exact matching > handling in drm because our uapi has a lot more warts, which we can't > change because no breaking userspace). > > So which one of the three below is the right approach? > > Aside, looking at the v4l solution I think there's also a confusion > about struct device representing a char device (which v4l directly > uses as its userspace interface refcounted thing, and which drm does > _not_ directly). And a struct device embedded into something like > platform_device or a virtual device, where a driver can bind to. My > question here is about the former, I don't care how cdev struct device > are cleaned up one bit. Now if other subsystems relies on the devres > cleanup behaviour we currently have because of such cdev usage, then > yeah first approach doesn't work (and I have a big surprised that use > case, but hey would actually learn something). > > End of aside, since again I want to figure out which of the tree > approaches it the right one. Not about how wrong one of them is, > ignoring the other three I laid out. And maybe there's even more > options for this. Sorry, been swamped with other things, give me a few days to get back to this, I need to dig into how you all are dealing with the virtual drivers. Doing this in the middle of the merge window is a bit rough :) thanks, greg k-h ___ dri-devel mailing list dri-devel@lists.freedesktop.org https://lists.freedesktop.org/mailman/listinfo/dri-devel
Re: [PATCH 01/44] drivers/base: Always release devres on device_del
On Fri, Apr 3, 2020 at 3:58 PM Daniel Vetter wrote:
>
> In drm we've added nice drm_device (the main gpu driver thing, which
> also represents the userspace interfaces and has everything else
> dangling off it) init functions using devres, devm_drm_dev_init and
> soon devm_drm_dev_alloc (this patch series adds that).
>
> A slight trouble is that drm_device itself holds a reference on the
> struct device it's sitting on top (for sysfs links and dmesg debug and
> lots of other things), so there's a reference loop. For real drivers
> this is broken at remove/unplug time, where all devres resources are
> released device_release_driver(), before the final device reference is
> dropped. So far so good.
>
> There's 2 exceptions:
> - drm/vkms|vgem: Virtual drivers for which we create a fake/virtual
> platform device to make them look more like normal devices to
> userspace. These aren't drivers in the driver model sense, we simple
> create a platform_device and register it.
>
> - drm/i915/selftests, where we create minimal mock devices, and again
> the selftests aren't proper drivers in the driver model sense.
>
> For these two cases the reference loop isn't broken, because devres is
> only cleaned up when the last device reference is dropped. But that's
> not happening, because the drm_device holds that last struct device
> reference.
>
> Thus far this wasn't a problem since the above cases simply
> hand-rolled their cleanup code. But I want to convert all drivers over
> to the devm_ versions, hence it would be really nice if these
> virtual/fake/mock uses-cases could also be managed with devres
> cleanup.
>
> I see three possible approaches:
Restarting this at the top level, because the discussion thus far just
ended in a long "you're doing it wrong", despite that I think we're
doing what v4l is doing (plus/minus that we can't do an exact matching
handling in drm because our uapi has a lot more warts, which we can't
change because no breaking userspace).
So which one of the three below is the right approach?
Aside, looking at the v4l solution I think there's also a confusion
about struct device representing a char device (which v4l directly
uses as its userspace interface refcounted thing, and which drm does
_not_ directly). And a struct device embedded into something like
platform_device or a virtual device, where a driver can bind to. My
question here is about the former, I don't care how cdev struct device
are cleaned up one bit. Now if other subsystems relies on the devres
cleanup behaviour we currently have because of such cdev usage, then
yeah first approach doesn't work (and I have a big surprised that use
case, but hey would actually learn something).
End of aside, since again I want to figure out which of the tree
approaches it the right one. Not about how wrong one of them is,
ignoring the other three I laid out. And maybe there's even more
options for this.
-Daniel
> - Clean up devres from device_del (or platform_device_unregister) even
> when no driver is bound. This seems like the simplest solution, but
> also the one with the widest impact, and what this patch implements.
> We might want to include more of the cleanup than just
> devres_release_all, but this is all I need to get my use case going.
>
> - Create a devres group and release that when we unbind. The code in
> virtual drivers gets a bit ugly, since every error case has a
> different cleanup code until we've chained everything
> (platform_device, devres group and then drm_device) together and a
> devres_release_group takes care of everything. Doable, but a bit
> confusing when I typed it out.
>
> - Convert the virtual drivers to real (in the device model sense)
> drivers. Feels like too much boilerplate for not much gain. And
> especially with the mock objects minimal mocking is kinda the goal,
> to limit the amount of accidentally pulled in code into our unit
> tests as much as possible.
>
> Either way I think time to discuss this a bit and figure out what's
> the recommended approach here.
>
> Signed-off-by: Daniel Vetter
> Cc: Greg Kroah-Hartman
> Cc: "Rafael J. Wysocki"
> ---
> drivers/base/dd.c | 2 ++
> 1 file changed, 2 insertions(+)
>
> diff --git a/drivers/base/dd.c b/drivers/base/dd.c
> index b25bcab2a26b..1bcfb0ff5f44 100644
> --- a/drivers/base/dd.c
> +++ b/drivers/base/dd.c
> @@ -1155,6 +1155,8 @@ static void __device_release_driver(struct device *dev,
> struct device *parent)
> dev);
>
> kobject_uevent(&dev->kobj, KOBJ_UNBIND);
> + } else {
> + devres_release_all(dev);
> }
> }
>
> --
> 2.25.1
>
--
Daniel Vetter
Software Engineer, Intel Corporation
+41 (0) 79 365 57 48 - http://blog.ffwll.ch
___
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Re: [PATCH 01/44] drivers/base: Always release devres on device_del
On Fri, Apr 3, 2020 at 5:15 PM Daniel Vetter wrote: > > On Fri, Apr 3, 2020 at 5:06 PM Greg Kroah-Hartman > wrote: > > > > On Fri, Apr 03, 2020 at 04:47:04PM +0200, Daniel Vetter wrote: > > > On Fri, Apr 3, 2020 at 4:17 PM Greg Kroah-Hartman > > > wrote: > > > > > > > > On Fri, Apr 03, 2020 at 03:57:45PM +0200, Daniel Vetter wrote: > > > > > In drm we've added nice drm_device (the main gpu driver thing, which > > > > > also represents the userspace interfaces and has everything else > > > > > dangling off it) init functions using devres, devm_drm_dev_init and > > > > > soon devm_drm_dev_alloc (this patch series adds that). > > > > > > > > > > A slight trouble is that drm_device itself holds a reference on the > > > > > struct device it's sitting on top (for sysfs links and dmesg debug and > > > > > lots of other things), so there's a reference loop. For real drivers > > > > > this is broken at remove/unplug time, where all devres resources are > > > > > released device_release_driver(), before the final device reference is > > > > > dropped. So far so good. > > > > > > > > > > There's 2 exceptions: > > > > > - drm/vkms|vgem: Virtual drivers for which we create a fake/virtual > > > > > platform device to make them look more like normal devices to > > > > > userspace. These aren't drivers in the driver model sense, we simple > > > > > create a platform_device and register it. > > > > > > > > That's a horrid abuse of platform devices, just use a "virtual" device > > > > please, create/remove it when you need it, and all should be fine. > > > > > > > > > - drm/i915/selftests, where we create minimal mock devices, and again > > > > > the selftests aren't proper drivers in the driver model sense. > > > > > > > > Again, virtual devices are best to use for this. > > > > > > Hm yeah, I guess we should fix that. i915 selftests do use raw struct > > > device though, and it's not really the problem. > > > > > > > > For these two cases the reference loop isn't broken, because devres is > > > > > only cleaned up when the last device reference is dropped. But that's > > > > > not happening, because the drm_device holds that last struct device > > > > > reference. > > > > > > > > > > Thus far this wasn't a problem since the above cases simply > > > > > hand-rolled their cleanup code. But I want to convert all drivers over > > > > > to the devm_ versions, hence it would be really nice if these > > > > > virtual/fake/mock uses-cases could also be managed with devres > > > > > cleanup. > > > > > > > > > > I see three possible approaches: > > > > > > > > > > - Clean up devres from device_del (or platform_device_unregister) even > > > > > when no driver is bound. This seems like the simplest solution, but > > > > > also the one with the widest impact, and what this patch implements. > > > > > We might want to include more of the cleanup than just > > > > > devres_release_all, but this is all I need to get my use case going. > > > > > > > > After device_del, you should never be using that structure again anyway. > > > > So why is there any "resource leak"? You can't recycle the structure, > > > > and you can't assign it to anything else, so eventually you have to do > > > > a final put on the thing, which will free up the resources. > > > > > > I guess I should have spent more time explaining this. There's two > > > references involved: > > > > > > - drm_device->dev points at the underlying struct device. The > > > drm_device holds a reference until it's fully cleaned up, so that we > > > can do nice stuff like use dev_ versions of printk functions, and you > > > always know that there's not going to be a use-after free. > > > > > > - now the other dependency is that as long as the device exists (not > > > just in memory, but in the device model, i.e. between device_add() and > > > device_del()) the drm_device should exist. So what we do in the > > > bus-specific remove/disconnect callback is that we call > > > drm_dev_unregister(). This drops the drm_device refcount that the drm > > > chardev was holding, to make sure that an open() on the chardev can > > > actually get at the memory without going boom. Then after the > > > drm_dev_unregister, again in the remove/disconnect callback of th > > > driver, there's a drm_dev_put(). Which might or might not be the final > > > drm_dev_put(), since if there's currently some open fd we keep the > > > refcount elevated, to avoid oopses and fun stuff like that. And > > > drm_device pointers get shared very widely, thanks to fun stuff like > > > dma_buf buffer sharing and dma_fence hw syncpt sharing across > > > processes and drivers. > > > > > > Once the final drm_dev_put() is called we also end up calling > > > put_device() and everything is happy. > > > > > > So far so good. > > > > > > Now the problem is that refcount is hard, and most drm drivers get it > > > wrong in some fashion or another, so I'm trying to solve all this with > > > more magic. > > > > Wait, no.
Re: [PATCH 01/44] drivers/base: Always release devres on device_del
On Fri, Apr 3, 2020 at 5:06 PM Greg Kroah-Hartman wrote: > > On Fri, Apr 03, 2020 at 04:47:04PM +0200, Daniel Vetter wrote: > > On Fri, Apr 3, 2020 at 4:17 PM Greg Kroah-Hartman > > wrote: > > > > > > On Fri, Apr 03, 2020 at 03:57:45PM +0200, Daniel Vetter wrote: > > > > In drm we've added nice drm_device (the main gpu driver thing, which > > > > also represents the userspace interfaces and has everything else > > > > dangling off it) init functions using devres, devm_drm_dev_init and > > > > soon devm_drm_dev_alloc (this patch series adds that). > > > > > > > > A slight trouble is that drm_device itself holds a reference on the > > > > struct device it's sitting on top (for sysfs links and dmesg debug and > > > > lots of other things), so there's a reference loop. For real drivers > > > > this is broken at remove/unplug time, where all devres resources are > > > > released device_release_driver(), before the final device reference is > > > > dropped. So far so good. > > > > > > > > There's 2 exceptions: > > > > - drm/vkms|vgem: Virtual drivers for which we create a fake/virtual > > > > platform device to make them look more like normal devices to > > > > userspace. These aren't drivers in the driver model sense, we simple > > > > create a platform_device and register it. > > > > > > That's a horrid abuse of platform devices, just use a "virtual" device > > > please, create/remove it when you need it, and all should be fine. > > > > > > > - drm/i915/selftests, where we create minimal mock devices, and again > > > > the selftests aren't proper drivers in the driver model sense. > > > > > > Again, virtual devices are best to use for this. > > > > Hm yeah, I guess we should fix that. i915 selftests do use raw struct > > device though, and it's not really the problem. > > > > > > For these two cases the reference loop isn't broken, because devres is > > > > only cleaned up when the last device reference is dropped. But that's > > > > not happening, because the drm_device holds that last struct device > > > > reference. > > > > > > > > Thus far this wasn't a problem since the above cases simply > > > > hand-rolled their cleanup code. But I want to convert all drivers over > > > > to the devm_ versions, hence it would be really nice if these > > > > virtual/fake/mock uses-cases could also be managed with devres > > > > cleanup. > > > > > > > > I see three possible approaches: > > > > > > > > - Clean up devres from device_del (or platform_device_unregister) even > > > > when no driver is bound. This seems like the simplest solution, but > > > > also the one with the widest impact, and what this patch implements. > > > > We might want to include more of the cleanup than just > > > > devres_release_all, but this is all I need to get my use case going. > > > > > > After device_del, you should never be using that structure again anyway. > > > So why is there any "resource leak"? You can't recycle the structure, > > > and you can't assign it to anything else, so eventually you have to do > > > a final put on the thing, which will free up the resources. > > > > I guess I should have spent more time explaining this. There's two > > references involved: > > > > - drm_device->dev points at the underlying struct device. The > > drm_device holds a reference until it's fully cleaned up, so that we > > can do nice stuff like use dev_ versions of printk functions, and you > > always know that there's not going to be a use-after free. > > > > - now the other dependency is that as long as the device exists (not > > just in memory, but in the device model, i.e. between device_add() and > > device_del()) the drm_device should exist. So what we do in the > > bus-specific remove/disconnect callback is that we call > > drm_dev_unregister(). This drops the drm_device refcount that the drm > > chardev was holding, to make sure that an open() on the chardev can > > actually get at the memory without going boom. Then after the > > drm_dev_unregister, again in the remove/disconnect callback of th > > driver, there's a drm_dev_put(). Which might or might not be the final > > drm_dev_put(), since if there's currently some open fd we keep the > > refcount elevated, to avoid oopses and fun stuff like that. And > > drm_device pointers get shared very widely, thanks to fun stuff like > > dma_buf buffer sharing and dma_fence hw syncpt sharing across > > processes and drivers. > > > > Once the final drm_dev_put() is called we also end up calling > > put_device() and everything is happy. > > > > So far so good. > > > > Now the problem is that refcount is hard, and most drm drivers get it > > wrong in some fashion or another, so I'm trying to solve all this with > > more magic. > > Wait, no. Fix the drivers. Seriously, don't try to "bust" the > reference count logic here. I guess still not clear. What I'm doing is fixing the drivers. But because they all get it wrong, I'm trying to hide as much of the refcounting as possible b
Re: [PATCH 01/44] drivers/base: Always release devres on device_del
On Fri, Apr 03, 2020 at 04:47:04PM +0200, Daniel Vetter wrote: > On Fri, Apr 3, 2020 at 4:17 PM Greg Kroah-Hartman > wrote: > > > > On Fri, Apr 03, 2020 at 03:57:45PM +0200, Daniel Vetter wrote: > > > In drm we've added nice drm_device (the main gpu driver thing, which > > > also represents the userspace interfaces and has everything else > > > dangling off it) init functions using devres, devm_drm_dev_init and > > > soon devm_drm_dev_alloc (this patch series adds that). > > > > > > A slight trouble is that drm_device itself holds a reference on the > > > struct device it's sitting on top (for sysfs links and dmesg debug and > > > lots of other things), so there's a reference loop. For real drivers > > > this is broken at remove/unplug time, where all devres resources are > > > released device_release_driver(), before the final device reference is > > > dropped. So far so good. > > > > > > There's 2 exceptions: > > > - drm/vkms|vgem: Virtual drivers for which we create a fake/virtual > > > platform device to make them look more like normal devices to > > > userspace. These aren't drivers in the driver model sense, we simple > > > create a platform_device and register it. > > > > That's a horrid abuse of platform devices, just use a "virtual" device > > please, create/remove it when you need it, and all should be fine. > > > > > - drm/i915/selftests, where we create minimal mock devices, and again > > > the selftests aren't proper drivers in the driver model sense. > > > > Again, virtual devices are best to use for this. > > Hm yeah, I guess we should fix that. i915 selftests do use raw struct > device though, and it's not really the problem. > > > > For these two cases the reference loop isn't broken, because devres is > > > only cleaned up when the last device reference is dropped. But that's > > > not happening, because the drm_device holds that last struct device > > > reference. > > > > > > Thus far this wasn't a problem since the above cases simply > > > hand-rolled their cleanup code. But I want to convert all drivers over > > > to the devm_ versions, hence it would be really nice if these > > > virtual/fake/mock uses-cases could also be managed with devres > > > cleanup. > > > > > > I see three possible approaches: > > > > > > - Clean up devres from device_del (or platform_device_unregister) even > > > when no driver is bound. This seems like the simplest solution, but > > > also the one with the widest impact, and what this patch implements. > > > We might want to include more of the cleanup than just > > > devres_release_all, but this is all I need to get my use case going. > > > > After device_del, you should never be using that structure again anyway. > > So why is there any "resource leak"? You can't recycle the structure, > > and you can't assign it to anything else, so eventually you have to do > > a final put on the thing, which will free up the resources. > > I guess I should have spent more time explaining this. There's two > references involved: > > - drm_device->dev points at the underlying struct device. The > drm_device holds a reference until it's fully cleaned up, so that we > can do nice stuff like use dev_ versions of printk functions, and you > always know that there's not going to be a use-after free. > > - now the other dependency is that as long as the device exists (not > just in memory, but in the device model, i.e. between device_add() and > device_del()) the drm_device should exist. So what we do in the > bus-specific remove/disconnect callback is that we call > drm_dev_unregister(). This drops the drm_device refcount that the drm > chardev was holding, to make sure that an open() on the chardev can > actually get at the memory without going boom. Then after the > drm_dev_unregister, again in the remove/disconnect callback of th > driver, there's a drm_dev_put(). Which might or might not be the final > drm_dev_put(), since if there's currently some open fd we keep the > refcount elevated, to avoid oopses and fun stuff like that. And > drm_device pointers get shared very widely, thanks to fun stuff like > dma_buf buffer sharing and dma_fence hw syncpt sharing across > processes and drivers. > > Once the final drm_dev_put() is called we also end up calling > put_device() and everything is happy. > > So far so good. > > Now the problem is that refcount is hard, and most drm drivers get it > wrong in some fashion or another, so I'm trying to solve all this with > more magic. Wait, no. Fix the drivers. Seriously, don't try to "bust" the reference count logic here. > Since all drivers need to have a drm_dev_put() at the end of their > driver's remove/disconnect callback we've added a devm_drm_dev_init > function which registers a devres action to do that drm_dev_put() at > device_del time (which might or might not be the final drm_dev_put()). > Nothing has changed thus far. > > Now this works really well because when you have a real driver model > d
Re: [PATCH 01/44] drivers/base: Always release devres on device_del
On Fri, Apr 03, 2020 at 04:51:33PM +0200, Daniel Vetter wrote: > On Fri, Apr 3, 2020 at 4:47 PM Daniel Vetter wrote: > > > > On Fri, Apr 3, 2020 at 4:17 PM Greg Kroah-Hartman > > wrote: > > > > > > On Fri, Apr 03, 2020 at 03:57:45PM +0200, Daniel Vetter wrote: > > > > In drm we've added nice drm_device (the main gpu driver thing, which > > > > also represents the userspace interfaces and has everything else > > > > dangling off it) init functions using devres, devm_drm_dev_init and > > > > soon devm_drm_dev_alloc (this patch series adds that). > > > > > > > > A slight trouble is that drm_device itself holds a reference on the > > > > struct device it's sitting on top (for sysfs links and dmesg debug and > > > > lots of other things), so there's a reference loop. For real drivers > > > > this is broken at remove/unplug time, where all devres resources are > > > > released device_release_driver(), before the final device reference is > > > > dropped. So far so good. > > > > > > > > There's 2 exceptions: > > > > - drm/vkms|vgem: Virtual drivers for which we create a fake/virtual > > > > platform device to make them look more like normal devices to > > > > userspace. These aren't drivers in the driver model sense, we simple > > > > create a platform_device and register it. > > > > > > That's a horrid abuse of platform devices, just use a "virtual" device > > > please, create/remove it when you need it, and all should be fine. > > > > > > > - drm/i915/selftests, where we create minimal mock devices, and again > > > > the selftests aren't proper drivers in the driver model sense. > > > > > > Again, virtual devices are best to use for this. > > > > Hm yeah, I guess we should fix that. i915 selftests do use raw struct > > device though, and it's not really the problem. > > > > > > For these two cases the reference loop isn't broken, because devres is > > > > only cleaned up when the last device reference is dropped. But that's > > > > not happening, because the drm_device holds that last struct device > > > > reference. > > > > > > > > Thus far this wasn't a problem since the above cases simply > > > > hand-rolled their cleanup code. But I want to convert all drivers over > > > > to the devm_ versions, hence it would be really nice if these > > > > virtual/fake/mock uses-cases could also be managed with devres > > > > cleanup. > > > > > > > > I see three possible approaches: > > > > > > > > - Clean up devres from device_del (or platform_device_unregister) even > > > > when no driver is bound. This seems like the simplest solution, but > > > > also the one with the widest impact, and what this patch implements. > > > > We might want to include more of the cleanup than just > > > > devres_release_all, but this is all I need to get my use case going. > > > > > > After device_del, you should never be using that structure again anyway. > > > So why is there any "resource leak"? You can't recycle the structure, > > > and you can't assign it to anything else, so eventually you have to do > > > a final put on the thing, which will free up the resources. > > > > I guess I should have spent more time explaining this. There's two > > references involved: > > > > - drm_device->dev points at the underlying struct device. The > > drm_device holds a reference until it's fully cleaned up, so that we > > can do nice stuff like use dev_ versions of printk functions, and you > > always know that there's not going to be a use-after free. > > > > - now the other dependency is that as long as the device exists (not > > just in memory, but in the device model, i.e. between device_add() and > > device_del()) the drm_device should exist. So what we do in the > > bus-specific remove/disconnect callback is that we call > > drm_dev_unregister(). This drops the drm_device refcount that the drm > > chardev was holding, to make sure that an open() on the chardev can > > actually get at the memory without going boom. Then after the > > drm_dev_unregister, again in the remove/disconnect callback of th > > driver, there's a drm_dev_put(). Which might or might not be the final > > drm_dev_put(), since if there's currently some open fd we keep the > > refcount elevated, to avoid oopses and fun stuff like that. And > > drm_device pointers get shared very widely, thanks to fun stuff like > > dma_buf buffer sharing and dma_fence hw syncpt sharing across > > processes and drivers. > > > > Once the final drm_dev_put() is called we also end up calling > > put_device() and everything is happy. > > > > So far so good. > > > > Now the problem is that refcount is hard, and most drm drivers get it > > wrong in some fashion or another, so I'm trying to solve all this with > > more magic. > > > > Since all drivers need to have a drm_dev_put() at the end of their > > driver's remove/disconnect callback we've added a devm_drm_dev_init > > function which registers a devres action to do that drm_dev_put() at > > device_del time (which might or mig
Re: [PATCH 01/44] drivers/base: Always release devres on device_del
On Fri, Apr 3, 2020 at 4:47 PM Daniel Vetter wrote: > > On Fri, Apr 3, 2020 at 4:17 PM Greg Kroah-Hartman > wrote: > > > > On Fri, Apr 03, 2020 at 03:57:45PM +0200, Daniel Vetter wrote: > > > In drm we've added nice drm_device (the main gpu driver thing, which > > > also represents the userspace interfaces and has everything else > > > dangling off it) init functions using devres, devm_drm_dev_init and > > > soon devm_drm_dev_alloc (this patch series adds that). > > > > > > A slight trouble is that drm_device itself holds a reference on the > > > struct device it's sitting on top (for sysfs links and dmesg debug and > > > lots of other things), so there's a reference loop. For real drivers > > > this is broken at remove/unplug time, where all devres resources are > > > released device_release_driver(), before the final device reference is > > > dropped. So far so good. > > > > > > There's 2 exceptions: > > > - drm/vkms|vgem: Virtual drivers for which we create a fake/virtual > > > platform device to make them look more like normal devices to > > > userspace. These aren't drivers in the driver model sense, we simple > > > create a platform_device and register it. > > > > That's a horrid abuse of platform devices, just use a "virtual" device > > please, create/remove it when you need it, and all should be fine. > > > > > - drm/i915/selftests, where we create minimal mock devices, and again > > > the selftests aren't proper drivers in the driver model sense. > > > > Again, virtual devices are best to use for this. > > Hm yeah, I guess we should fix that. i915 selftests do use raw struct > device though, and it's not really the problem. > > > > For these two cases the reference loop isn't broken, because devres is > > > only cleaned up when the last device reference is dropped. But that's > > > not happening, because the drm_device holds that last struct device > > > reference. > > > > > > Thus far this wasn't a problem since the above cases simply > > > hand-rolled their cleanup code. But I want to convert all drivers over > > > to the devm_ versions, hence it would be really nice if these > > > virtual/fake/mock uses-cases could also be managed with devres > > > cleanup. > > > > > > I see three possible approaches: > > > > > > - Clean up devres from device_del (or platform_device_unregister) even > > > when no driver is bound. This seems like the simplest solution, but > > > also the one with the widest impact, and what this patch implements. > > > We might want to include more of the cleanup than just > > > devres_release_all, but this is all I need to get my use case going. > > > > After device_del, you should never be using that structure again anyway. > > So why is there any "resource leak"? You can't recycle the structure, > > and you can't assign it to anything else, so eventually you have to do > > a final put on the thing, which will free up the resources. > > I guess I should have spent more time explaining this. There's two > references involved: > > - drm_device->dev points at the underlying struct device. The > drm_device holds a reference until it's fully cleaned up, so that we > can do nice stuff like use dev_ versions of printk functions, and you > always know that there's not going to be a use-after free. > > - now the other dependency is that as long as the device exists (not > just in memory, but in the device model, i.e. between device_add() and > device_del()) the drm_device should exist. So what we do in the > bus-specific remove/disconnect callback is that we call > drm_dev_unregister(). This drops the drm_device refcount that the drm > chardev was holding, to make sure that an open() on the chardev can > actually get at the memory without going boom. Then after the > drm_dev_unregister, again in the remove/disconnect callback of th > driver, there's a drm_dev_put(). Which might or might not be the final > drm_dev_put(), since if there's currently some open fd we keep the > refcount elevated, to avoid oopses and fun stuff like that. And > drm_device pointers get shared very widely, thanks to fun stuff like > dma_buf buffer sharing and dma_fence hw syncpt sharing across > processes and drivers. > > Once the final drm_dev_put() is called we also end up calling > put_device() and everything is happy. > > So far so good. > > Now the problem is that refcount is hard, and most drm drivers get it > wrong in some fashion or another, so I'm trying to solve all this with > more magic. > > Since all drivers need to have a drm_dev_put() at the end of their > driver's remove/disconnect callback we've added a devm_drm_dev_init > function which registers a devres action to do that drm_dev_put() at > device_del time (which might or might not be the final drm_dev_put()). > Nothing has changed thus far. > > Now this works really well because when you have a real driver model > driver attached, then device_del ends up calling devres_release_all(), > which ends up triggering the multi-st
Re: [PATCH 01/44] drivers/base: Always release devres on device_del
On Fri, Apr 3, 2020 at 4:17 PM Greg Kroah-Hartman wrote: > > On Fri, Apr 03, 2020 at 03:57:45PM +0200, Daniel Vetter wrote: > > In drm we've added nice drm_device (the main gpu driver thing, which > > also represents the userspace interfaces and has everything else > > dangling off it) init functions using devres, devm_drm_dev_init and > > soon devm_drm_dev_alloc (this patch series adds that). > > > > A slight trouble is that drm_device itself holds a reference on the > > struct device it's sitting on top (for sysfs links and dmesg debug and > > lots of other things), so there's a reference loop. For real drivers > > this is broken at remove/unplug time, where all devres resources are > > released device_release_driver(), before the final device reference is > > dropped. So far so good. > > > > There's 2 exceptions: > > - drm/vkms|vgem: Virtual drivers for which we create a fake/virtual > > platform device to make them look more like normal devices to > > userspace. These aren't drivers in the driver model sense, we simple > > create a platform_device and register it. > > That's a horrid abuse of platform devices, just use a "virtual" device > please, create/remove it when you need it, and all should be fine. > > > - drm/i915/selftests, where we create minimal mock devices, and again > > the selftests aren't proper drivers in the driver model sense. > > Again, virtual devices are best to use for this. Hm yeah, I guess we should fix that. i915 selftests do use raw struct device though, and it's not really the problem. > > For these two cases the reference loop isn't broken, because devres is > > only cleaned up when the last device reference is dropped. But that's > > not happening, because the drm_device holds that last struct device > > reference. > > > > Thus far this wasn't a problem since the above cases simply > > hand-rolled their cleanup code. But I want to convert all drivers over > > to the devm_ versions, hence it would be really nice if these > > virtual/fake/mock uses-cases could also be managed with devres > > cleanup. > > > > I see three possible approaches: > > > > - Clean up devres from device_del (or platform_device_unregister) even > > when no driver is bound. This seems like the simplest solution, but > > also the one with the widest impact, and what this patch implements. > > We might want to include more of the cleanup than just > > devres_release_all, but this is all I need to get my use case going. > > After device_del, you should never be using that structure again anyway. > So why is there any "resource leak"? You can't recycle the structure, > and you can't assign it to anything else, so eventually you have to do > a final put on the thing, which will free up the resources. I guess I should have spent more time explaining this. There's two references involved: - drm_device->dev points at the underlying struct device. The drm_device holds a reference until it's fully cleaned up, so that we can do nice stuff like use dev_ versions of printk functions, and you always know that there's not going to be a use-after free. - now the other dependency is that as long as the device exists (not just in memory, but in the device model, i.e. between device_add() and device_del()) the drm_device should exist. So what we do in the bus-specific remove/disconnect callback is that we call drm_dev_unregister(). This drops the drm_device refcount that the drm chardev was holding, to make sure that an open() on the chardev can actually get at the memory without going boom. Then after the drm_dev_unregister, again in the remove/disconnect callback of th driver, there's a drm_dev_put(). Which might or might not be the final drm_dev_put(), since if there's currently some open fd we keep the refcount elevated, to avoid oopses and fun stuff like that. And drm_device pointers get shared very widely, thanks to fun stuff like dma_buf buffer sharing and dma_fence hw syncpt sharing across processes and drivers. Once the final drm_dev_put() is called we also end up calling put_device() and everything is happy. So far so good. Now the problem is that refcount is hard, and most drm drivers get it wrong in some fashion or another, so I'm trying to solve all this with more magic. Since all drivers need to have a drm_dev_put() at the end of their driver's remove/disconnect callback we've added a devm_drm_dev_init function which registers a devres action to do that drm_dev_put() at device_del time (which might or might not be the final drm_dev_put()). Nothing has changed thus far. Now this works really well because when you have a real driver model driver attached, then device_del ends up calling devres_release_all(), which ends up triggering the multi-stage cleanup of drm_devices. But if you do _not_ have a real driver attached, then device_del does nothing wrt devres cleanup. Instead this is delayed until the final put_device(). Unfortunately that final put_device() will never happen, bec
Re: [PATCH 01/44] drivers/base: Always release devres on device_del
On Fri, Apr 03, 2020 at 03:57:45PM +0200, Daniel Vetter wrote: > In drm we've added nice drm_device (the main gpu driver thing, which > also represents the userspace interfaces and has everything else > dangling off it) init functions using devres, devm_drm_dev_init and > soon devm_drm_dev_alloc (this patch series adds that). > > A slight trouble is that drm_device itself holds a reference on the > struct device it's sitting on top (for sysfs links and dmesg debug and > lots of other things), so there's a reference loop. For real drivers > this is broken at remove/unplug time, where all devres resources are > released device_release_driver(), before the final device reference is > dropped. So far so good. > > There's 2 exceptions: > - drm/vkms|vgem: Virtual drivers for which we create a fake/virtual > platform device to make them look more like normal devices to > userspace. These aren't drivers in the driver model sense, we simple > create a platform_device and register it. That's a horrid abuse of platform devices, just use a "virtual" device please, create/remove it when you need it, and all should be fine. > - drm/i915/selftests, where we create minimal mock devices, and again > the selftests aren't proper drivers in the driver model sense. Again, virtual devices are best to use for this. > For these two cases the reference loop isn't broken, because devres is > only cleaned up when the last device reference is dropped. But that's > not happening, because the drm_device holds that last struct device > reference. > > Thus far this wasn't a problem since the above cases simply > hand-rolled their cleanup code. But I want to convert all drivers over > to the devm_ versions, hence it would be really nice if these > virtual/fake/mock uses-cases could also be managed with devres > cleanup. > > I see three possible approaches: > > - Clean up devres from device_del (or platform_device_unregister) even > when no driver is bound. This seems like the simplest solution, but > also the one with the widest impact, and what this patch implements. > We might want to include more of the cleanup than just > devres_release_all, but this is all I need to get my use case going. After device_del, you should never be using that structure again anyway. So why is there any "resource leak"? You can't recycle the structure, and you can't assign it to anything else, so eventually you have to do a final put on the thing, which will free up the resources. And then all should be fine, right? But, by putting the freeing here, you can still have a "live" device that thinks it has resources availble that it can access, but yet they are now gone. Yeah, it's probably not ever going to really happen, but the lifecycles of dynamic devices are tough to "prove" at times, and I worry that freeing things this early is going to cause odd disconnect issues. thanks, greg k-h ___ dri-devel mailing list dri-devel@lists.freedesktop.org https://lists.freedesktop.org/mailman/listinfo/dri-devel
[PATCH 01/44] drivers/base: Always release devres on device_del
In drm we've added nice drm_device (the main gpu driver thing, which
also represents the userspace interfaces and has everything else
dangling off it) init functions using devres, devm_drm_dev_init and
soon devm_drm_dev_alloc (this patch series adds that).
A slight trouble is that drm_device itself holds a reference on the
struct device it's sitting on top (for sysfs links and dmesg debug and
lots of other things), so there's a reference loop. For real drivers
this is broken at remove/unplug time, where all devres resources are
released device_release_driver(), before the final device reference is
dropped. So far so good.
There's 2 exceptions:
- drm/vkms|vgem: Virtual drivers for which we create a fake/virtual
platform device to make them look more like normal devices to
userspace. These aren't drivers in the driver model sense, we simple
create a platform_device and register it.
- drm/i915/selftests, where we create minimal mock devices, and again
the selftests aren't proper drivers in the driver model sense.
For these two cases the reference loop isn't broken, because devres is
only cleaned up when the last device reference is dropped. But that's
not happening, because the drm_device holds that last struct device
reference.
Thus far this wasn't a problem since the above cases simply
hand-rolled their cleanup code. But I want to convert all drivers over
to the devm_ versions, hence it would be really nice if these
virtual/fake/mock uses-cases could also be managed with devres
cleanup.
I see three possible approaches:
- Clean up devres from device_del (or platform_device_unregister) even
when no driver is bound. This seems like the simplest solution, but
also the one with the widest impact, and what this patch implements.
We might want to include more of the cleanup than just
devres_release_all, but this is all I need to get my use case going.
- Create a devres group and release that when we unbind. The code in
virtual drivers gets a bit ugly, since every error case has a
different cleanup code until we've chained everything
(platform_device, devres group and then drm_device) together and a
devres_release_group takes care of everything. Doable, but a bit
confusing when I typed it out.
- Convert the virtual drivers to real (in the device model sense)
drivers. Feels like too much boilerplate for not much gain. And
especially with the mock objects minimal mocking is kinda the goal,
to limit the amount of accidentally pulled in code into our unit
tests as much as possible.
Either way I think time to discuss this a bit and figure out what's
the recommended approach here.
Signed-off-by: Daniel Vetter
Cc: Greg Kroah-Hartman
Cc: "Rafael J. Wysocki"
---
drivers/base/dd.c | 2 ++
1 file changed, 2 insertions(+)
diff --git a/drivers/base/dd.c b/drivers/base/dd.c
index b25bcab2a26b..1bcfb0ff5f44 100644
--- a/drivers/base/dd.c
+++ b/drivers/base/dd.c
@@ -1155,6 +1155,8 @@ static void __device_release_driver(struct device *dev,
struct device *parent)
dev);
kobject_uevent(&dev->kobj, KOBJ_UNBIND);
+ } else {
+ devres_release_all(dev);
}
}
--
2.25.1
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