Re: [PATCH 02/13] driver core: Remove the link if there is no driver with AUTO flag
On Tue, 2019-03-12 at 16:17 -0700, Evan Green wrote:
> On Tue, Mar 12, 2019 at 7:21 AM Matthias Brugger
> wrote:
> >
> >
> >
> > On 05/03/2019 20:03, Evan Green wrote:
> > > On Wed, Feb 27, 2019 at 6:33 AM Yong Wu wrote:
> > >>
> > >> On Mon, 2019-02-25 at 15:53 -0800, Evan Green wrote:
> > >>> On Mon, Dec 31, 2018 at 8:52 PM Yong Wu wrote:
> >
> > DL_FLAG_AUTOREMOVE_CONSUMER/SUPPLIER means "Remove the link
> > automatically on consumer/supplier driver unbind", that means we should
> > remove whole the device_link when there is no this driver no matter
> > what
> > the ref_count of the link is.
> >
> > CC: Greg Kroah-Hartman
> > Signed-off-by: Yong Wu
> > ---
> > The ref_count of our device_link normally is over 1. When the consumer
> > device driver is removed, whole the device_link should be removed.
> > Thus, I add this patch.
> > ---
> > >>>
> > >>> I will admit to reading about device links for the first time while
> > >>> reviewing this patch, but I don't really get this. Why use a kref at
> > >>> all if we're just going to ignore its value? For instance, I see that
> > >>> if you call device_link_add() with the same supplier and consumer, it
> > >>> uses the kref to return the same link. That machinery is broken with
> > >>> your change. Although I don't see any uses of it, you might also
> > >>> expect a supplier or consumer could do a kref_get() on the link it got
> > >>> back from device_link_add(), and have a reasonable expectation that
> > >>> the link wouldn't be freed out from under it. This would also be
> > >>> broken.
> > >>>
> > >>> Can you explain why your device_links normally have a reference count
> > 1,
> > >>
> > >> I use device link between the smi-larb device and the iommu-consumer
> > >> device. Take a example, smi-larb1 have 4 VDEC ports. From 4/13 in this
> > >> patchset, we use device_link to link the VDEC device and the smi-larb1
> > >> device in the function(mtk_iommu_config). since there are 4 ports, it
> > >> will call device_link_add 4 times.
> > >>
> > >>>
> > >>> and why those additional references can't be cleaned up in an
> > >>> orderly fashion?
> > >>
> > >> If the iommu-consume device(like VDEC above) is removed, It should enter
> > >> device_links_driver_cleanup which only ref_put one time. I guess whole
> > >> the link should be removed at that time.
> > >
> > > It seems like Robin had some suggestions about using
> > > mtk_iommu_add_device() rather than the attach_dev() to set the links
> > > up, and then track them for removal in the corresponding
> > > remove_device() callback. Then you wouldn't need this change, right?
Hi Evan, sorry for reply you so late. I have not got time to try
this(Put it in the add_device), But I guess it works.
At that time the ref_cnt here should be 1, then this patch is
unnecessary.
> > >
> >
> > FYI, Evan the patch is queued for v5.1-rc1 as
> > 0fe6f7874d46 ("driver core: Remove the link if there is no driver with AUTO
> > flag")
> >
> > So if you think there is something wrong with it, then please provide a fix
> > or
> > raise awareness :)
>
> Oh. Thanks for the heads-up Matthias. It's pretty weird that we have
> the kref there whose count we just completely ignore. I'll try to find
> some time to submit a patch.
Thanks very much if you improve this.
> -Evan
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Re: [PATCH 02/13] driver core: Remove the link if there is no driver with AUTO flag
On Tue, Mar 12, 2019 at 7:21 AM Matthias Brugger wrote:
>
>
>
> On 05/03/2019 20:03, Evan Green wrote:
> > On Wed, Feb 27, 2019 at 6:33 AM Yong Wu wrote:
> >>
> >> On Mon, 2019-02-25 at 15:53 -0800, Evan Green wrote:
> >>> On Mon, Dec 31, 2018 at 8:52 PM Yong Wu wrote:
>
> DL_FLAG_AUTOREMOVE_CONSUMER/SUPPLIER means "Remove the link
> automatically on consumer/supplier driver unbind", that means we should
> remove whole the device_link when there is no this driver no matter what
> the ref_count of the link is.
>
> CC: Greg Kroah-Hartman
> Signed-off-by: Yong Wu
> ---
> The ref_count of our device_link normally is over 1. When the consumer
> device driver is removed, whole the device_link should be removed.
> Thus, I add this patch.
> ---
> >>>
> >>> I will admit to reading about device links for the first time while
> >>> reviewing this patch, but I don't really get this. Why use a kref at
> >>> all if we're just going to ignore its value? For instance, I see that
> >>> if you call device_link_add() with the same supplier and consumer, it
> >>> uses the kref to return the same link. That machinery is broken with
> >>> your change. Although I don't see any uses of it, you might also
> >>> expect a supplier or consumer could do a kref_get() on the link it got
> >>> back from device_link_add(), and have a reasonable expectation that
> >>> the link wouldn't be freed out from under it. This would also be
> >>> broken.
> >>>
> >>> Can you explain why your device_links normally have a reference count
> 1,
> >>
> >> I use device link between the smi-larb device and the iommu-consumer
> >> device. Take a example, smi-larb1 have 4 VDEC ports. From 4/13 in this
> >> patchset, we use device_link to link the VDEC device and the smi-larb1
> >> device in the function(mtk_iommu_config). since there are 4 ports, it
> >> will call device_link_add 4 times.
> >>
> >>>
> >>> and why those additional references can't be cleaned up in an
> >>> orderly fashion?
> >>
> >> If the iommu-consume device(like VDEC above) is removed, It should enter
> >> device_links_driver_cleanup which only ref_put one time. I guess whole
> >> the link should be removed at that time.
> >
> > It seems like Robin had some suggestions about using
> > mtk_iommu_add_device() rather than the attach_dev() to set the links
> > up, and then track them for removal in the corresponding
> > remove_device() callback. Then you wouldn't need this change, right?
> >
>
> FYI, Evan the patch is queued for v5.1-rc1 as
> 0fe6f7874d46 ("driver core: Remove the link if there is no driver with AUTO
> flag")
>
> So if you think there is something wrong with it, then please provide a fix or
> raise awareness :)
Oh. Thanks for the heads-up Matthias. It's pretty weird that we have
the kref there whose count we just completely ignore. I'll try to find
some time to submit a patch.
-Evan
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Re: [PATCH 02/13] driver core: Remove the link if there is no driver with AUTO flag
On 05/03/2019 20:03, Evan Green wrote:
> On Wed, Feb 27, 2019 at 6:33 AM Yong Wu wrote:
>>
>> On Mon, 2019-02-25 at 15:53 -0800, Evan Green wrote:
>>> On Mon, Dec 31, 2018 at 8:52 PM Yong Wu wrote:
DL_FLAG_AUTOREMOVE_CONSUMER/SUPPLIER means "Remove the link
automatically on consumer/supplier driver unbind", that means we should
remove whole the device_link when there is no this driver no matter what
the ref_count of the link is.
CC: Greg Kroah-Hartman
Signed-off-by: Yong Wu
---
The ref_count of our device_link normally is over 1. When the consumer
device driver is removed, whole the device_link should be removed.
Thus, I add this patch.
---
>>>
>>> I will admit to reading about device links for the first time while
>>> reviewing this patch, but I don't really get this. Why use a kref at
>>> all if we're just going to ignore its value? For instance, I see that
>>> if you call device_link_add() with the same supplier and consumer, it
>>> uses the kref to return the same link. That machinery is broken with
>>> your change. Although I don't see any uses of it, you might also
>>> expect a supplier or consumer could do a kref_get() on the link it got
>>> back from device_link_add(), and have a reasonable expectation that
>>> the link wouldn't be freed out from under it. This would also be
>>> broken.
>>>
>>> Can you explain why your device_links normally have a reference count
1,
>>
>> I use device link between the smi-larb device and the iommu-consumer
>> device. Take a example, smi-larb1 have 4 VDEC ports. From 4/13 in this
>> patchset, we use device_link to link the VDEC device and the smi-larb1
>> device in the function(mtk_iommu_config). since there are 4 ports, it
>> will call device_link_add 4 times.
>>
>>>
>>> and why those additional references can't be cleaned up in an
>>> orderly fashion?
>>
>> If the iommu-consume device(like VDEC above) is removed, It should enter
>> device_links_driver_cleanup which only ref_put one time. I guess whole
>> the link should be removed at that time.
>
> It seems like Robin had some suggestions about using
> mtk_iommu_add_device() rather than the attach_dev() to set the links
> up, and then track them for removal in the corresponding
> remove_device() callback. Then you wouldn't need this change, right?
>
FYI, Evan the patch is queued for v5.1-rc1 as
0fe6f7874d46 ("driver core: Remove the link if there is no driver with AUTO
flag")
So if you think there is something wrong with it, then please provide a fix or
raise awareness :)
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Re: [PATCH 02/13] driver core: Remove the link if there is no driver with AUTO flag
On Wed, Feb 27, 2019 at 6:33 AM Yong Wu wrote: > > On Mon, 2019-02-25 at 15:53 -0800, Evan Green wrote: > > On Mon, Dec 31, 2018 at 8:52 PM Yong Wu wrote: > > > > > > DL_FLAG_AUTOREMOVE_CONSUMER/SUPPLIER means "Remove the link > > > automatically on consumer/supplier driver unbind", that means we should > > > remove whole the device_link when there is no this driver no matter what > > > the ref_count of the link is. > > > > > > CC: Greg Kroah-Hartman > > > Signed-off-by: Yong Wu > > > --- > > > The ref_count of our device_link normally is over 1. When the consumer > > > device driver is removed, whole the device_link should be removed. > > > Thus, I add this patch. > > > --- > > > > I will admit to reading about device links for the first time while > > reviewing this patch, but I don't really get this. Why use a kref at > > all if we're just going to ignore its value? For instance, I see that > > if you call device_link_add() with the same supplier and consumer, it > > uses the kref to return the same link. That machinery is broken with > > your change. Although I don't see any uses of it, you might also > > expect a supplier or consumer could do a kref_get() on the link it got > > back from device_link_add(), and have a reasonable expectation that > > the link wouldn't be freed out from under it. This would also be > > broken. > > > > Can you explain why your device_links normally have a reference count > > >1, > > I use device link between the smi-larb device and the iommu-consumer > device. Take a example, smi-larb1 have 4 VDEC ports. From 4/13 in this > patchset, we use device_link to link the VDEC device and the smi-larb1 > device in the function(mtk_iommu_config). since there are 4 ports, it > will call device_link_add 4 times. > > > > > and why those additional references can't be cleaned up in an > > orderly fashion? > > If the iommu-consume device(like VDEC above) is removed, It should enter > device_links_driver_cleanup which only ref_put one time. I guess whole > the link should be removed at that time. It seems like Robin had some suggestions about using mtk_iommu_add_device() rather than the attach_dev() to set the links up, and then track them for removal in the corresponding remove_device() callback. Then you wouldn't need this change, right? ___ iommu mailing list iommu@lists.linux-foundation.org https://lists.linuxfoundation.org/mailman/listinfo/iommu
Re: [PATCH 02/13] driver core: Remove the link if there is no driver with AUTO flag
On Mon, 2019-02-25 at 15:53 -0800, Evan Green wrote: > On Mon, Dec 31, 2018 at 8:52 PM Yong Wu wrote: > > > > DL_FLAG_AUTOREMOVE_CONSUMER/SUPPLIER means "Remove the link > > automatically on consumer/supplier driver unbind", that means we should > > remove whole the device_link when there is no this driver no matter what > > the ref_count of the link is. > > > > CC: Greg Kroah-Hartman > > Signed-off-by: Yong Wu > > --- > > The ref_count of our device_link normally is over 1. When the consumer > > device driver is removed, whole the device_link should be removed. > > Thus, I add this patch. > > --- > > I will admit to reading about device links for the first time while > reviewing this patch, but I don't really get this. Why use a kref at > all if we're just going to ignore its value? For instance, I see that > if you call device_link_add() with the same supplier and consumer, it > uses the kref to return the same link. That machinery is broken with > your change. Although I don't see any uses of it, you might also > expect a supplier or consumer could do a kref_get() on the link it got > back from device_link_add(), and have a reasonable expectation that > the link wouldn't be freed out from under it. This would also be > broken. > > Can you explain why your device_links normally have a reference count > >1, I use device link between the smi-larb device and the iommu-consumer device. Take a example, smi-larb1 have 4 VDEC ports. From 4/13 in this patchset, we use device_link to link the VDEC device and the smi-larb1 device in the function(mtk_iommu_config). since there are 4 ports, it will call device_link_add 4 times. > > and why those additional references can't be cleaned up in an > orderly fashion? If the iommu-consume device(like VDEC above) is removed, It should enter device_links_driver_cleanup which only ref_put one time. I guess whole the link should be removed at that time. > > (To be honest, I don't really understand the case for the AUTOREMOVE > flags at all. Is there some case where the party that set up the link > can't tear it down? Or is this a way to devm_ify the link, where devm > itself doesn't work because the links themselves stall out that > mechanism?) ___ iommu mailing list iommu@lists.linux-foundation.org https://lists.linuxfoundation.org/mailman/listinfo/iommu
Re: [PATCH 02/13] driver core: Remove the link if there is no driver with AUTO flag
On Mon, Dec 31, 2018 at 8:52 PM Yong Wu wrote: > > DL_FLAG_AUTOREMOVE_CONSUMER/SUPPLIER means "Remove the link > automatically on consumer/supplier driver unbind", that means we should > remove whole the device_link when there is no this driver no matter what > the ref_count of the link is. > > CC: Greg Kroah-Hartman > Signed-off-by: Yong Wu > --- > The ref_count of our device_link normally is over 1. When the consumer > device driver is removed, whole the device_link should be removed. > Thus, I add this patch. > --- I will admit to reading about device links for the first time while reviewing this patch, but I don't really get this. Why use a kref at all if we're just going to ignore its value? For instance, I see that if you call device_link_add() with the same supplier and consumer, it uses the kref to return the same link. That machinery is broken with your change. Although I don't see any uses of it, you might also expect a supplier or consumer could do a kref_get() on the link it got back from device_link_add(), and have a reasonable expectation that the link wouldn't be freed out from under it. This would also be broken. Can you explain why your device_links normally have a reference count >1, and why those additional references can't be cleaned up in an orderly fashion? (To be honest, I don't really understand the case for the AUTOREMOVE flags at all. Is there some case where the party that set up the link can't tear it down? Or is this a way to devm_ify the link, where devm itself doesn't work because the links themselves stall out that mechanism?) ___ iommu mailing list iommu@lists.linux-foundation.org https://lists.linuxfoundation.org/mailman/listinfo/iommu
[PATCH 02/13] driver core: Remove the link if there is no driver with AUTO flag
DL_FLAG_AUTOREMOVE_CONSUMER/SUPPLIER means "Remove the link automatically on consumer/supplier driver unbind", that means we should remove whole the device_link when there is no this driver no matter what the ref_count of the link is. CC: Greg Kroah-Hartman Signed-off-by: Yong Wu --- The ref_count of our device_link normally is over 1. When the consumer device driver is removed, whole the device_link should be removed. Thus, I add this patch. --- drivers/base/core.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) diff --git a/drivers/base/core.c b/drivers/base/core.c index 04bbcd7..4f3c5bc 100644 --- a/drivers/base/core.c +++ b/drivers/base/core.c @@ -511,7 +511,7 @@ static void __device_links_no_driver(struct device *dev) continue; if (link->flags & DL_FLAG_AUTOREMOVE_CONSUMER) - kref_put(>kref, __device_link_del); + __device_link_del(>kref); else if (link->status != DL_STATE_SUPPLIER_UNBIND) WRITE_ONCE(link->status, DL_STATE_AVAILABLE); } @@ -556,7 +556,7 @@ void device_links_driver_cleanup(struct device *dev) */ if (link->status == DL_STATE_SUPPLIER_UNBIND && link->flags & DL_FLAG_AUTOREMOVE_SUPPLIER) - kref_put(>kref, __device_link_del); + __device_link_del(>kref); WRITE_ONCE(link->status, DL_STATE_DORMANT); } -- 1.9.1 ___ iommu mailing list iommu@lists.linux-foundation.org https://lists.linuxfoundation.org/mailman/listinfo/iommu
