Re: [PATCH v3 3/4] drm/bridge: Add devm_drm_bridge_add()
On Fri, Jun 03, 2022 at 07:56:16AM -0700, Doug Anderson wrote: > Hi, > > On Fri, Jun 3, 2022 at 7:14 AM Maxime Ripard wrote: > > > > On Fri, Jun 03, 2022 at 01:19:16PM +0300, Dmitry Baryshkov wrote: > > > On Fri, 3 Jun 2022 at 11:21, Maxime Ripard wrote: > > > > > > > > On Tue, May 31, 2022 at 02:06:34PM -0700, Doug Anderson wrote: > > > > > On Mon, May 23, 2022 at 10:00 AM Doug Anderson > > > > > wrote: > > > > > > On Sat, May 21, 2022 at 2:17 AM Maxime Ripard > > > > > > wrote: > > > > > > > On Tue, May 10, 2022 at 12:29:43PM -0700, Douglas Anderson wrote: > > > > > > > > This adds a devm managed version of drm_bridge_add(). Like other > > > > > > > > "devm" function listed in drm_bridge.h, this function takes an > > > > > > > > explicit "dev" to use for the lifetime management. A few notes: > > > > > > > > * In general we have a "struct device" for bridges that makes a > > > > > > > > good > > > > > > > > candidate for where the lifetime matches exactly what we want. > > > > > > > > * The "bridge->dev->dev" device appears to be the encoder > > > > > > > > device. That's not the right device to use for lifetime > > > > > > > > management. > > > > > > > > > > > > > > > > Suggested-by: Dmitry Baryshkov > > > > > > > > Signed-off-by: Douglas Anderson > > > > > > > > > > > > > > If we are to introduce more managed helpers, I think it'd be > > > > > > > wiser to > > > > > > > introduce them as DRM-managed, and not device managed. > > > > > > > > > > > > > > Otherwise, you'll end up in a weird state when a device has been > > > > > > > removed > > > > > > > but the DRM device is still around. > > > > > > > > > > > > I'm kinda confused. In this case there is no DRM device for the > > > > > > bridge > > > > > > and, as per my CL description, "bridge-dev->dev" appears to be the > > > > > > encoder device. I wasn't personally involved in discussions about > > > > > > it, > > > > > > but I was under the impression that this was expected / normal. Thus > > > > > > we can't make this DRM-managed. > > > > > > > > > > Since I didn't hear a reply, > > > > > > > > Gah, I replied but it looks like somehow it never reached the ML... > > > > > > > > Here was my original reply: > > > > > > > > > > > This adds a devm managed version of drm_bridge_add(). Like other > > > > > > > "devm" function listed in drm_bridge.h, this function takes an > > > > > > > explicit "dev" to use for the lifetime management. A few notes: > > > > > > > * In general we have a "struct device" for bridges that makes a > > > > > > > good > > > > > > > candidate for where the lifetime matches exactly what we want. > > > > > > > * The "bridge->dev->dev" device appears to be the encoder > > > > > > > device. That's not the right device to use for lifetime > > > > > > > management. > > > > > > > > > > > > > > Suggested-by: Dmitry Baryshkov > > > > > > > Signed-off-by: Douglas Anderson > > > > > > > > > > > > If we are to introduce more managed helpers, I think it'd be wiser > > > > > > to > > > > > > introduce them as DRM-managed, and not device managed. > > > > > > > > > > > > Otherwise, you'll end up in a weird state when a device has been > > > > > > removed > > > > > > but the DRM device is still around. > > > > >=20 > > > > > I'm kinda confused. In this case there is no DRM device for the bridge > > > > > and, as per my CL description, "bridge-dev->dev" appears to be the > > > > > encoder device. > > > > > > > > bridge->dev seems right though? > > > > > > > > > I wasn't personally involved in discussions about it, but I was under > > > > > the impression that this was expected / normal. Thus we can't make > > > > > this DRM-managed. > > > > > > > > Still, I don't think devm is the right solution to this either. > > > > > > > > The underlying issue is two-fold: > > > > > > > > - Encoders can have a pointer to a bridge through of_drm_find_bridge > > > > or similar. However, bridges are traditionally tied to their device > > > > lifetime (by calling drm_bridge_add in probe, and drm_bridge_remove > > > > in remove). Encoders will typically be tied to the DRM device > > > > however, and that one sticks around until the last application > > > > closes it. We can thus very easily end up with a dangling pointer, > > > > and a use-after-free. > > > > > > > > - It's not the case yet, but it doesn't seem far fetch to expose > > > > properties of bridges to the userspace. In that case, the userspace > > > > would be likely to still hold references to objects that aren't > > > > there anymore when the bridge is gone. > > > > > > > > The first is obviously a larger concern, but if we can find a solution > > > > that would accomodate the second it would be great. > > > > > > > > As far as I can see, we should fix in two steps: > > > > > > > > - in drm_bridge_attach, we should add a device-managed call that will > > > > unregister the main DRM device. We don't allow to probe the main DRM > >
Re: [PATCH v3 3/4] drm/bridge: Add devm_drm_bridge_add()
On Sat, May 21, 2022 at 11:17:51AM +0200, Maxime Ripard wrote: > Hi, > > On Tue, May 10, 2022 at 12:29:43PM -0700, Douglas Anderson wrote: > > This adds a devm managed version of drm_bridge_add(). Like other > > "devm" function listed in drm_bridge.h, this function takes an > > explicit "dev" to use for the lifetime management. A few notes: > > * In general we have a "struct device" for bridges that makes a good > > candidate for where the lifetime matches exactly what we want. > > * The "bridge->dev->dev" device appears to be the encoder > > device. That's not the right device to use for lifetime management. > > > > Suggested-by: Dmitry Baryshkov > > Signed-off-by: Douglas Anderson > > If we are to introduce more managed helpers, I think it'd be wiser to > introduce them as DRM-managed, and not device managed. > > Otherwise, you'll end up in a weird state when a device has been removed > but the DRM device is still around. Top-level post since I didn't see any good place to reply in the thread below: - devm is for device stuff, which drm_bridge is (it's not uapi visible in any way or fasion) - drmm is for uapi visible stuff (like drm_encoder) Yes the uapi-visible stuff can outlive the device-related pieces. The way to handle this is: - drm_dev_unplug() when the device disappears underneath you (or just a part, I guess the infra for that doesn't exist yet and maybe we should add it). - drm_dev_enter/exit wrapped around the device related parts. Iow, this patch here I think is the right direction, and gets my Reviewed-by: Daniel Vetter But also, it's definitely not a complete solution as the discussion in the thread here points out. Cheers, Daniel -- Daniel Vetter Software Engineer, Intel Corporation http://blog.ffwll.ch
Re: [PATCH v3 3/4] drm/bridge: Add devm_drm_bridge_add()
Hi, On Fri, Jun 3, 2022 at 7:14 AM Maxime Ripard wrote: > > On Fri, Jun 03, 2022 at 01:19:16PM +0300, Dmitry Baryshkov wrote: > > On Fri, 3 Jun 2022 at 11:21, Maxime Ripard wrote: > > > > > > On Tue, May 31, 2022 at 02:06:34PM -0700, Doug Anderson wrote: > > > > On Mon, May 23, 2022 at 10:00 AM Doug Anderson > > > > wrote: > > > > > On Sat, May 21, 2022 at 2:17 AM Maxime Ripard > > > > > wrote: > > > > > > On Tue, May 10, 2022 at 12:29:43PM -0700, Douglas Anderson wrote: > > > > > > > This adds a devm managed version of drm_bridge_add(). Like other > > > > > > > "devm" function listed in drm_bridge.h, this function takes an > > > > > > > explicit "dev" to use for the lifetime management. A few notes: > > > > > > > * In general we have a "struct device" for bridges that makes a > > > > > > > good > > > > > > > candidate for where the lifetime matches exactly what we want. > > > > > > > * The "bridge->dev->dev" device appears to be the encoder > > > > > > > device. That's not the right device to use for lifetime > > > > > > > management. > > > > > > > > > > > > > > Suggested-by: Dmitry Baryshkov > > > > > > > Signed-off-by: Douglas Anderson > > > > > > > > > > > > If we are to introduce more managed helpers, I think it'd be wiser > > > > > > to > > > > > > introduce them as DRM-managed, and not device managed. > > > > > > > > > > > > Otherwise, you'll end up in a weird state when a device has been > > > > > > removed > > > > > > but the DRM device is still around. > > > > > > > > > > I'm kinda confused. In this case there is no DRM device for the bridge > > > > > and, as per my CL description, "bridge-dev->dev" appears to be the > > > > > encoder device. I wasn't personally involved in discussions about it, > > > > > but I was under the impression that this was expected / normal. Thus > > > > > we can't make this DRM-managed. > > > > > > > > Since I didn't hear a reply, > > > > > > Gah, I replied but it looks like somehow it never reached the ML... > > > > > > Here was my original reply: > > > > > > > > > This adds a devm managed version of drm_bridge_add(). Like other > > > > > > "devm" function listed in drm_bridge.h, this function takes an > > > > > > explicit "dev" to use for the lifetime management. A few notes: > > > > > > * In general we have a "struct device" for bridges that makes a good > > > > > > candidate for where the lifetime matches exactly what we want. > > > > > > * The "bridge->dev->dev" device appears to be the encoder > > > > > > device. That's not the right device to use for lifetime > > > > > > management. > > > > > > > > > > > > Suggested-by: Dmitry Baryshkov > > > > > > Signed-off-by: Douglas Anderson > > > > > > > > > > If we are to introduce more managed helpers, I think it'd be wiser to > > > > > introduce them as DRM-managed, and not device managed. > > > > > > > > > > Otherwise, you'll end up in a weird state when a device has been > > > > > removed > > > > > but the DRM device is still around. > > > >=20 > > > > I'm kinda confused. In this case there is no DRM device for the bridge > > > > and, as per my CL description, "bridge-dev->dev" appears to be the > > > > encoder device. > > > > > > bridge->dev seems right though? > > > > > > > I wasn't personally involved in discussions about it, but I was under > > > > the impression that this was expected / normal. Thus we can't make > > > > this DRM-managed. > > > > > > Still, I don't think devm is the right solution to this either. > > > > > > The underlying issue is two-fold: > > > > > > - Encoders can have a pointer to a bridge through of_drm_find_bridge > > > or similar. However, bridges are traditionally tied to their device > > > lifetime (by calling drm_bridge_add in probe, and drm_bridge_remove > > > in remove). Encoders will typically be tied to the DRM device > > > however, and that one sticks around until the last application > > > closes it. We can thus very easily end up with a dangling pointer, > > > and a use-after-free. > > > > > > - It's not the case yet, but it doesn't seem far fetch to expose > > > properties of bridges to the userspace. In that case, the userspace > > > would be likely to still hold references to objects that aren't > > > there anymore when the bridge is gone. > > > > > > The first is obviously a larger concern, but if we can find a solution > > > that would accomodate the second it would be great. > > > > > > As far as I can see, we should fix in two steps: > > > > > > - in drm_bridge_attach, we should add a device-managed call that will > > > unregister the main DRM device. We don't allow to probe the main DRM > > > device when the bridge isn't there yet in most case, so it makes > > > sense to remove it once the bridge is no longer there as well. > > > > The problem is that I do not see a good way to unregister the main DRM > > device outside of it's driver code. > > That's what drmm helpers are doing though:
Re: [PATCH v3 3/4] drm/bridge: Add devm_drm_bridge_add()
On Fri, Jun 03, 2022 at 06:52:05AM -0700, Doug Anderson wrote: > On Fri, Jun 3, 2022 at 3:19 AM Dmitry Baryshkov > wrote: > > On Fri, 3 Jun 2022 at 11:21, Maxime Ripard wrote: > > > > > > On Tue, May 31, 2022 at 02:06:34PM -0700, Doug Anderson wrote: > > > > On Mon, May 23, 2022 at 10:00 AM Doug Anderson > > > > wrote: > > > > > On Sat, May 21, 2022 at 2:17 AM Maxime Ripard > > > > > wrote: > > > > > > On Tue, May 10, 2022 at 12:29:43PM -0700, Douglas Anderson wrote: > > > > > > > This adds a devm managed version of drm_bridge_add(). Like other > > > > > > > "devm" function listed in drm_bridge.h, this function takes an > > > > > > > explicit "dev" to use for the lifetime management. A few notes: > > > > > > > * In general we have a "struct device" for bridges that makes a > > > > > > > good > > > > > > > candidate for where the lifetime matches exactly what we want. > > > > > > > * The "bridge->dev->dev" device appears to be the encoder > > > > > > > device. That's not the right device to use for lifetime > > > > > > > management. > > > > > > > > > > > > > > Suggested-by: Dmitry Baryshkov > > > > > > > Signed-off-by: Douglas Anderson > > > > > > > > > > > > If we are to introduce more managed helpers, I think it'd be wiser > > > > > > to > > > > > > introduce them as DRM-managed, and not device managed. > > > > > > > > > > > > Otherwise, you'll end up in a weird state when a device has been > > > > > > removed > > > > > > but the DRM device is still around. > > > > > > > > > > I'm kinda confused. In this case there is no DRM device for the bridge > > > > > and, as per my CL description, "bridge-dev->dev" appears to be the > > > > > encoder device. I wasn't personally involved in discussions about it, > > > > > but I was under the impression that this was expected / normal. Thus > > > > > we can't make this DRM-managed. > > > > > > > > Since I didn't hear a reply, > > > > > > Gah, I replied but it looks like somehow it never reached the ML... > > > > > > Here was my original reply: > > > > > > > > > This adds a devm managed version of drm_bridge_add(). Like other > > > > > > "devm" function listed in drm_bridge.h, this function takes an > > > > > > explicit "dev" to use for the lifetime management. A few notes: > > > > > > * In general we have a "struct device" for bridges that makes a good > > > > > > candidate for where the lifetime matches exactly what we want. > > > > > > * The "bridge->dev->dev" device appears to be the encoder > > > > > > device. That's not the right device to use for lifetime > > > > > > management. > > > > > > > > > > > > Suggested-by: Dmitry Baryshkov > > > > > > Signed-off-by: Douglas Anderson > > > > > > > > > > If we are to introduce more managed helpers, I think it'd be wiser to > > > > > introduce them as DRM-managed, and not device managed. > > > > > > > > > > Otherwise, you'll end up in a weird state when a device has been > > > > > removed > > > > > but the DRM device is still around. > > > >=20 > > > > I'm kinda confused. In this case there is no DRM device for the bridge > > > > and, as per my CL description, "bridge-dev->dev" appears to be the > > > > encoder device. > > > > > > bridge->dev seems right though? > > > > > > > I wasn't personally involved in discussions about it, but I was under > > > > the impression that this was expected / normal. Thus we can't make > > > > this DRM-managed. > > > > > > Still, I don't think devm is the right solution to this either. > > > > > > The underlying issue is two-fold: > > > > > > - Encoders can have a pointer to a bridge through of_drm_find_bridge > > > or similar. However, bridges are traditionally tied to their device > > > lifetime (by calling drm_bridge_add in probe, and drm_bridge_remove > > > in remove). Encoders will typically be tied to the DRM device > > > however, and that one sticks around until the last application > > > closes it. We can thus very easily end up with a dangling pointer, > > > and a use-after-free. > > > > > > - It's not the case yet, but it doesn't seem far fetch to expose > > > properties of bridges to the userspace. In that case, the userspace > > > would be likely to still hold references to objects that aren't > > > there anymore when the bridge is gone. > > > > > > The first is obviously a larger concern, but if we can find a solution > > > that would accomodate the second it would be great. > > > > > > As far as I can see, we should fix in two steps: > > > > > > - in drm_bridge_attach, we should add a device-managed call that will > > > unregister the main DRM device. We don't allow to probe the main DRM > > > device when the bridge isn't there yet in most case, so it makes > > > sense to remove it once the bridge is no longer there as well. > > > > The problem is that I do not see a good way to unregister the main DRM > > device outside of it's driver code. > > > > > > > > - When the DRM device is removed, have
Re: [PATCH v3 3/4] drm/bridge: Add devm_drm_bridge_add()
On Fri, Jun 03, 2022 at 01:19:16PM +0300, Dmitry Baryshkov wrote: > On Fri, 3 Jun 2022 at 11:21, Maxime Ripard wrote: > > > > On Tue, May 31, 2022 at 02:06:34PM -0700, Doug Anderson wrote: > > > On Mon, May 23, 2022 at 10:00 AM Doug Anderson > > > wrote: > > > > On Sat, May 21, 2022 at 2:17 AM Maxime Ripard wrote: > > > > > On Tue, May 10, 2022 at 12:29:43PM -0700, Douglas Anderson wrote: > > > > > > This adds a devm managed version of drm_bridge_add(). Like other > > > > > > "devm" function listed in drm_bridge.h, this function takes an > > > > > > explicit "dev" to use for the lifetime management. A few notes: > > > > > > * In general we have a "struct device" for bridges that makes a good > > > > > > candidate for where the lifetime matches exactly what we want. > > > > > > * The "bridge->dev->dev" device appears to be the encoder > > > > > > device. That's not the right device to use for lifetime > > > > > > management. > > > > > > > > > > > > Suggested-by: Dmitry Baryshkov > > > > > > Signed-off-by: Douglas Anderson > > > > > > > > > > If we are to introduce more managed helpers, I think it'd be wiser to > > > > > introduce them as DRM-managed, and not device managed. > > > > > > > > > > Otherwise, you'll end up in a weird state when a device has been > > > > > removed > > > > > but the DRM device is still around. > > > > > > > > I'm kinda confused. In this case there is no DRM device for the bridge > > > > and, as per my CL description, "bridge-dev->dev" appears to be the > > > > encoder device. I wasn't personally involved in discussions about it, > > > > but I was under the impression that this was expected / normal. Thus > > > > we can't make this DRM-managed. > > > > > > Since I didn't hear a reply, > > > > Gah, I replied but it looks like somehow it never reached the ML... > > > > Here was my original reply: > > > > > > > This adds a devm managed version of drm_bridge_add(). Like other > > > > > "devm" function listed in drm_bridge.h, this function takes an > > > > > explicit "dev" to use for the lifetime management. A few notes: > > > > > * In general we have a "struct device" for bridges that makes a good > > > > > candidate for where the lifetime matches exactly what we want. > > > > > * The "bridge->dev->dev" device appears to be the encoder > > > > > device. That's not the right device to use for lifetime management. > > > > > > > > > > Suggested-by: Dmitry Baryshkov > > > > > Signed-off-by: Douglas Anderson > > > > > > > > If we are to introduce more managed helpers, I think it'd be wiser to > > > > introduce them as DRM-managed, and not device managed. > > > > > > > > Otherwise, you'll end up in a weird state when a device has been removed > > > > but the DRM device is still around. > > >=20 > > > I'm kinda confused. In this case there is no DRM device for the bridge > > > and, as per my CL description, "bridge-dev->dev" appears to be the > > > encoder device. > > > > bridge->dev seems right though? > > > > > I wasn't personally involved in discussions about it, but I was under > > > the impression that this was expected / normal. Thus we can't make > > > this DRM-managed. > > > > Still, I don't think devm is the right solution to this either. > > > > The underlying issue is two-fold: > > > > - Encoders can have a pointer to a bridge through of_drm_find_bridge > > or similar. However, bridges are traditionally tied to their device > > lifetime (by calling drm_bridge_add in probe, and drm_bridge_remove > > in remove). Encoders will typically be tied to the DRM device > > however, and that one sticks around until the last application > > closes it. We can thus very easily end up with a dangling pointer, > > and a use-after-free. > > > > - It's not the case yet, but it doesn't seem far fetch to expose > > properties of bridges to the userspace. In that case, the userspace > > would be likely to still hold references to objects that aren't > > there anymore when the bridge is gone. > > > > The first is obviously a larger concern, but if we can find a solution > > that would accomodate the second it would be great. > > > > As far as I can see, we should fix in two steps: > > > > - in drm_bridge_attach, we should add a device-managed call that will > > unregister the main DRM device. We don't allow to probe the main DRM > > device when the bridge isn't there yet in most case, so it makes > > sense to remove it once the bridge is no longer there as well. > > The problem is that I do not see a good way to unregister the main DRM > device outside of it's driver code. That's what drmm helpers are doing though: they'll defer the cleanup until the last user has closed its fd. > > - When the DRM device is removed, have the core cleanup any bridge > > registered. That will remove the need to have drm_bridge_remove in > > the first place. > > > > > I'll assume that my response addressed your concerns. Assuming I get >
Re: [PATCH v3 3/4] drm/bridge: Add devm_drm_bridge_add()
Hi, On Fri, Jun 3, 2022 at 3:19 AM Dmitry Baryshkov wrote: > > On Fri, 3 Jun 2022 at 11:21, Maxime Ripard wrote: > > > > On Tue, May 31, 2022 at 02:06:34PM -0700, Doug Anderson wrote: > > > On Mon, May 23, 2022 at 10:00 AM Doug Anderson > > > wrote: > > > > On Sat, May 21, 2022 at 2:17 AM Maxime Ripard wrote: > > > > > On Tue, May 10, 2022 at 12:29:43PM -0700, Douglas Anderson wrote: > > > > > > This adds a devm managed version of drm_bridge_add(). Like other > > > > > > "devm" function listed in drm_bridge.h, this function takes an > > > > > > explicit "dev" to use for the lifetime management. A few notes: > > > > > > * In general we have a "struct device" for bridges that makes a good > > > > > > candidate for where the lifetime matches exactly what we want. > > > > > > * The "bridge->dev->dev" device appears to be the encoder > > > > > > device. That's not the right device to use for lifetime > > > > > > management. > > > > > > > > > > > > Suggested-by: Dmitry Baryshkov > > > > > > Signed-off-by: Douglas Anderson > > > > > > > > > > If we are to introduce more managed helpers, I think it'd be wiser to > > > > > introduce them as DRM-managed, and not device managed. > > > > > > > > > > Otherwise, you'll end up in a weird state when a device has been > > > > > removed > > > > > but the DRM device is still around. > > > > > > > > I'm kinda confused. In this case there is no DRM device for the bridge > > > > and, as per my CL description, "bridge-dev->dev" appears to be the > > > > encoder device. I wasn't personally involved in discussions about it, > > > > but I was under the impression that this was expected / normal. Thus > > > > we can't make this DRM-managed. > > > > > > Since I didn't hear a reply, > > > > Gah, I replied but it looks like somehow it never reached the ML... > > > > Here was my original reply: > > > > > > > This adds a devm managed version of drm_bridge_add(). Like other > > > > > "devm" function listed in drm_bridge.h, this function takes an > > > > > explicit "dev" to use for the lifetime management. A few notes: > > > > > * In general we have a "struct device" for bridges that makes a good > > > > > candidate for where the lifetime matches exactly what we want. > > > > > * The "bridge->dev->dev" device appears to be the encoder > > > > > device. That's not the right device to use for lifetime management. > > > > > > > > > > Suggested-by: Dmitry Baryshkov > > > > > Signed-off-by: Douglas Anderson > > > > > > > > If we are to introduce more managed helpers, I think it'd be wiser to > > > > introduce them as DRM-managed, and not device managed. > > > > > > > > Otherwise, you'll end up in a weird state when a device has been removed > > > > but the DRM device is still around. > > >=20 > > > I'm kinda confused. In this case there is no DRM device for the bridge > > > and, as per my CL description, "bridge-dev->dev" appears to be the > > > encoder device. > > > > bridge->dev seems right though? > > > > > I wasn't personally involved in discussions about it, but I was under > > > the impression that this was expected / normal. Thus we can't make > > > this DRM-managed. > > > > Still, I don't think devm is the right solution to this either. > > > > The underlying issue is two-fold: > > > > - Encoders can have a pointer to a bridge through of_drm_find_bridge > > or similar. However, bridges are traditionally tied to their device > > lifetime (by calling drm_bridge_add in probe, and drm_bridge_remove > > in remove). Encoders will typically be tied to the DRM device > > however, and that one sticks around until the last application > > closes it. We can thus very easily end up with a dangling pointer, > > and a use-after-free. > > > > - It's not the case yet, but it doesn't seem far fetch to expose > > properties of bridges to the userspace. In that case, the userspace > > would be likely to still hold references to objects that aren't > > there anymore when the bridge is gone. > > > > The first is obviously a larger concern, but if we can find a solution > > that would accomodate the second it would be great. > > > > As far as I can see, we should fix in two steps: > > > > - in drm_bridge_attach, we should add a device-managed call that will > > unregister the main DRM device. We don't allow to probe the main DRM > > device when the bridge isn't there yet in most case, so it makes > > sense to remove it once the bridge is no longer there as well. > > The problem is that I do not see a good way to unregister the main DRM > device outside of it's driver code. > > > > > - When the DRM device is removed, have the core cleanup any bridge > > registered. That will remove the need to have drm_bridge_remove in > > the first place. > > > > > I'll assume that my response addressed your concerns. Assuming I get > > > reviews for the other two patches in this series I'll plan to land > > > this with Dmitry's review. > >
Re: [PATCH v3 3/4] drm/bridge: Add devm_drm_bridge_add()
On Fri, 3 Jun 2022 at 11:21, Maxime Ripard wrote: > > On Tue, May 31, 2022 at 02:06:34PM -0700, Doug Anderson wrote: > > On Mon, May 23, 2022 at 10:00 AM Doug Anderson > > wrote: > > > On Sat, May 21, 2022 at 2:17 AM Maxime Ripard wrote: > > > > On Tue, May 10, 2022 at 12:29:43PM -0700, Douglas Anderson wrote: > > > > > This adds a devm managed version of drm_bridge_add(). Like other > > > > > "devm" function listed in drm_bridge.h, this function takes an > > > > > explicit "dev" to use for the lifetime management. A few notes: > > > > > * In general we have a "struct device" for bridges that makes a good > > > > > candidate for where the lifetime matches exactly what we want. > > > > > * The "bridge->dev->dev" device appears to be the encoder > > > > > device. That's not the right device to use for lifetime management. > > > > > > > > > > Suggested-by: Dmitry Baryshkov > > > > > Signed-off-by: Douglas Anderson > > > > > > > > If we are to introduce more managed helpers, I think it'd be wiser to > > > > introduce them as DRM-managed, and not device managed. > > > > > > > > Otherwise, you'll end up in a weird state when a device has been removed > > > > but the DRM device is still around. > > > > > > I'm kinda confused. In this case there is no DRM device for the bridge > > > and, as per my CL description, "bridge-dev->dev" appears to be the > > > encoder device. I wasn't personally involved in discussions about it, > > > but I was under the impression that this was expected / normal. Thus > > > we can't make this DRM-managed. > > > > Since I didn't hear a reply, > > Gah, I replied but it looks like somehow it never reached the ML... > > Here was my original reply: > > > > > This adds a devm managed version of drm_bridge_add(). Like other > > > > "devm" function listed in drm_bridge.h, this function takes an > > > > explicit "dev" to use for the lifetime management. A few notes: > > > > * In general we have a "struct device" for bridges that makes a good > > > > candidate for where the lifetime matches exactly what we want. > > > > * The "bridge->dev->dev" device appears to be the encoder > > > > device. That's not the right device to use for lifetime management. > > > > > > > > Suggested-by: Dmitry Baryshkov > > > > Signed-off-by: Douglas Anderson > > > > > > If we are to introduce more managed helpers, I think it'd be wiser to > > > introduce them as DRM-managed, and not device managed. > > > > > > Otherwise, you'll end up in a weird state when a device has been removed > > > but the DRM device is still around. > >=20 > > I'm kinda confused. In this case there is no DRM device for the bridge > > and, as per my CL description, "bridge-dev->dev" appears to be the > > encoder device. > > bridge->dev seems right though? > > > I wasn't personally involved in discussions about it, but I was under > > the impression that this was expected / normal. Thus we can't make > > this DRM-managed. > > Still, I don't think devm is the right solution to this either. > > The underlying issue is two-fold: > > - Encoders can have a pointer to a bridge through of_drm_find_bridge > or similar. However, bridges are traditionally tied to their device > lifetime (by calling drm_bridge_add in probe, and drm_bridge_remove > in remove). Encoders will typically be tied to the DRM device > however, and that one sticks around until the last application > closes it. We can thus very easily end up with a dangling pointer, > and a use-after-free. > > - It's not the case yet, but it doesn't seem far fetch to expose > properties of bridges to the userspace. In that case, the userspace > would be likely to still hold references to objects that aren't > there anymore when the bridge is gone. > > The first is obviously a larger concern, but if we can find a solution > that would accomodate the second it would be great. > > As far as I can see, we should fix in two steps: > > - in drm_bridge_attach, we should add a device-managed call that will > unregister the main DRM device. We don't allow to probe the main DRM > device when the bridge isn't there yet in most case, so it makes > sense to remove it once the bridge is no longer there as well. The problem is that I do not see a good way to unregister the main DRM device outside of it's driver code. > > - When the DRM device is removed, have the core cleanup any bridge > registered. That will remove the need to have drm_bridge_remove in > the first place. > > > I'll assume that my response addressed your concerns. Assuming I get > > reviews for the other two patches in this series I'll plan to land > > this with Dmitry's review. > > I still don't think it's a good idea to merge it. It gives an illusion > of being safe, but it's really far from it. It is more of removing the boilerplate code spread over all the drivers rather than about particular safety. I'd propose to land devm_drm_bridge_add (and deprecate
Re: [PATCH v3 3/4] drm/bridge: Add devm_drm_bridge_add()
On Tue, May 31, 2022 at 02:06:34PM -0700, Doug Anderson wrote: > On Mon, May 23, 2022 at 10:00 AM Doug Anderson wrote: > > On Sat, May 21, 2022 at 2:17 AM Maxime Ripard wrote: > > > On Tue, May 10, 2022 at 12:29:43PM -0700, Douglas Anderson wrote: > > > > This adds a devm managed version of drm_bridge_add(). Like other > > > > "devm" function listed in drm_bridge.h, this function takes an > > > > explicit "dev" to use for the lifetime management. A few notes: > > > > * In general we have a "struct device" for bridges that makes a good > > > > candidate for where the lifetime matches exactly what we want. > > > > * The "bridge->dev->dev" device appears to be the encoder > > > > device. That's not the right device to use for lifetime management. > > > > > > > > Suggested-by: Dmitry Baryshkov > > > > Signed-off-by: Douglas Anderson > > > > > > If we are to introduce more managed helpers, I think it'd be wiser to > > > introduce them as DRM-managed, and not device managed. > > > > > > Otherwise, you'll end up in a weird state when a device has been removed > > > but the DRM device is still around. > > > > I'm kinda confused. In this case there is no DRM device for the bridge > > and, as per my CL description, "bridge-dev->dev" appears to be the > > encoder device. I wasn't personally involved in discussions about it, > > but I was under the impression that this was expected / normal. Thus > > we can't make this DRM-managed. > > Since I didn't hear a reply, Gah, I replied but it looks like somehow it never reached the ML... Here was my original reply: > > > This adds a devm managed version of drm_bridge_add(). Like other > > > "devm" function listed in drm_bridge.h, this function takes an > > > explicit "dev" to use for the lifetime management. A few notes: > > > * In general we have a "struct device" for bridges that makes a good > > > candidate for where the lifetime matches exactly what we want. > > > * The "bridge->dev->dev" device appears to be the encoder > > > device. That's not the right device to use for lifetime management. > > > > > > Suggested-by: Dmitry Baryshkov > > > Signed-off-by: Douglas Anderson > > > > If we are to introduce more managed helpers, I think it'd be wiser to > > introduce them as DRM-managed, and not device managed. > > > > Otherwise, you'll end up in a weird state when a device has been removed > > but the DRM device is still around. >=20 > I'm kinda confused. In this case there is no DRM device for the bridge > and, as per my CL description, "bridge-dev->dev" appears to be the > encoder device. bridge->dev seems right though? > I wasn't personally involved in discussions about it, but I was under > the impression that this was expected / normal. Thus we can't make > this DRM-managed. Still, I don't think devm is the right solution to this either. The underlying issue is two-fold: - Encoders can have a pointer to a bridge through of_drm_find_bridge or similar. However, bridges are traditionally tied to their device lifetime (by calling drm_bridge_add in probe, and drm_bridge_remove in remove). Encoders will typically be tied to the DRM device however, and that one sticks around until the last application closes it. We can thus very easily end up with a dangling pointer, and a use-after-free. - It's not the case yet, but it doesn't seem far fetch to expose properties of bridges to the userspace. In that case, the userspace would be likely to still hold references to objects that aren't there anymore when the bridge is gone. The first is obviously a larger concern, but if we can find a solution that would accomodate the second it would be great. As far as I can see, we should fix in two steps: - in drm_bridge_attach, we should add a device-managed call that will unregister the main DRM device. We don't allow to probe the main DRM device when the bridge isn't there yet in most case, so it makes sense to remove it once the bridge is no longer there as well. - When the DRM device is removed, have the core cleanup any bridge registered. That will remove the need to have drm_bridge_remove in the first place. > I'll assume that my response addressed your concerns. Assuming I get > reviews for the other two patches in this series I'll plan to land > this with Dmitry's review. I still don't think it's a good idea to merge it. It gives an illusion of being safe, but it's really far from it. Maxime
Re: [PATCH v3 3/4] drm/bridge: Add devm_drm_bridge_add()
Maxime, On Mon, May 23, 2022 at 10:00 AM Doug Anderson wrote: > > Hi, > > On Sat, May 21, 2022 at 2:17 AM Maxime Ripard wrote: > > > > Hi, > > > > On Tue, May 10, 2022 at 12:29:43PM -0700, Douglas Anderson wrote: > > > This adds a devm managed version of drm_bridge_add(). Like other > > > "devm" function listed in drm_bridge.h, this function takes an > > > explicit "dev" to use for the lifetime management. A few notes: > > > * In general we have a "struct device" for bridges that makes a good > > > candidate for where the lifetime matches exactly what we want. > > > * The "bridge->dev->dev" device appears to be the encoder > > > device. That's not the right device to use for lifetime management. > > > > > > Suggested-by: Dmitry Baryshkov > > > Signed-off-by: Douglas Anderson > > > > If we are to introduce more managed helpers, I think it'd be wiser to > > introduce them as DRM-managed, and not device managed. > > > > Otherwise, you'll end up in a weird state when a device has been removed > > but the DRM device is still around. > > I'm kinda confused. In this case there is no DRM device for the bridge > and, as per my CL description, "bridge-dev->dev" appears to be the > encoder device. I wasn't personally involved in discussions about it, > but I was under the impression that this was expected / normal. Thus > we can't make this DRM-managed. Since I didn't hear a reply, I'll assume that my response addressed your concerns. Assuming I get reviews for the other two patches in this series I'll plan to land this with Dmitry's review. -Doug
Re: [PATCH v3 3/4] drm/bridge: Add devm_drm_bridge_add()
Hi, On Sat, May 21, 2022 at 2:17 AM Maxime Ripard wrote: > > Hi, > > On Tue, May 10, 2022 at 12:29:43PM -0700, Douglas Anderson wrote: > > This adds a devm managed version of drm_bridge_add(). Like other > > "devm" function listed in drm_bridge.h, this function takes an > > explicit "dev" to use for the lifetime management. A few notes: > > * In general we have a "struct device" for bridges that makes a good > > candidate for where the lifetime matches exactly what we want. > > * The "bridge->dev->dev" device appears to be the encoder > > device. That's not the right device to use for lifetime management. > > > > Suggested-by: Dmitry Baryshkov > > Signed-off-by: Douglas Anderson > > If we are to introduce more managed helpers, I think it'd be wiser to > introduce them as DRM-managed, and not device managed. > > Otherwise, you'll end up in a weird state when a device has been removed > but the DRM device is still around. I'm kinda confused. In this case there is no DRM device for the bridge and, as per my CL description, "bridge-dev->dev" appears to be the encoder device. I wasn't personally involved in discussions about it, but I was under the impression that this was expected / normal. Thus we can't make this DRM-managed. -Doug
Re: [PATCH v3 3/4] drm/bridge: Add devm_drm_bridge_add()
Hi, On Tue, May 10, 2022 at 12:29:43PM -0700, Douglas Anderson wrote: > This adds a devm managed version of drm_bridge_add(). Like other > "devm" function listed in drm_bridge.h, this function takes an > explicit "dev" to use for the lifetime management. A few notes: > * In general we have a "struct device" for bridges that makes a good > candidate for where the lifetime matches exactly what we want. > * The "bridge->dev->dev" device appears to be the encoder > device. That's not the right device to use for lifetime management. > > Suggested-by: Dmitry Baryshkov > Signed-off-by: Douglas Anderson If we are to introduce more managed helpers, I think it'd be wiser to introduce them as DRM-managed, and not device managed. Otherwise, you'll end up in a weird state when a device has been removed but the DRM device is still around. Maxime
Re: [PATCH v3 3/4] drm/bridge: Add devm_drm_bridge_add()
Hi, On Tue, May 10, 2022 at 5:22 PM Dmitry Baryshkov wrote: > > On Tue, 10 May 2022 at 22:30, Douglas Anderson wrote: > > > > This adds a devm managed version of drm_bridge_add(). Like other > > "devm" function listed in drm_bridge.h, this function takes an > > explicit "dev" to use for the lifetime management. A few notes: > > * In general we have a "struct device" for bridges that makes a good > > candidate for where the lifetime matches exactly what we want. > > * The "bridge->dev->dev" device appears to be the encoder > > device. That's not the right device to use for lifetime management. > > > > Suggested-by: Dmitry Baryshkov > > Signed-off-by: Douglas Anderson > > Reviewed-by: Dmitry Baryshkov Thanks for the review! For now I'll hold off on landing this until sometime has time to review the other patches in the series. While not technically required, it seems weird to add the devm function without any callers. -Doug
Re: [PATCH v3 3/4] drm/bridge: Add devm_drm_bridge_add()
On Tue, 10 May 2022 at 22:30, Douglas Anderson wrote:
>
> This adds a devm managed version of drm_bridge_add(). Like other
> "devm" function listed in drm_bridge.h, this function takes an
> explicit "dev" to use for the lifetime management. A few notes:
> * In general we have a "struct device" for bridges that makes a good
> candidate for where the lifetime matches exactly what we want.
> * The "bridge->dev->dev" device appears to be the encoder
> device. That's not the right device to use for lifetime management.
>
> Suggested-by: Dmitry Baryshkov
> Signed-off-by: Douglas Anderson
Reviewed-by: Dmitry Baryshkov
> ---
>
> Changes in v3:
> - Patch ("drm/bridge: Add devm_drm_bridge_add()") new for v3.
>
> drivers/gpu/drm/drm_bridge.c | 23 +++
> include/drm/drm_bridge.h | 1 +
> 2 files changed, 24 insertions(+)
>
> diff --git a/drivers/gpu/drm/drm_bridge.c b/drivers/gpu/drm/drm_bridge.c
> index c96847fc0ebc..e275b4ca344b 100644
> --- a/drivers/gpu/drm/drm_bridge.c
> +++ b/drivers/gpu/drm/drm_bridge.c
> @@ -170,6 +170,29 @@ void drm_bridge_add(struct drm_bridge *bridge)
> }
> EXPORT_SYMBOL(drm_bridge_add);
>
> +static void drm_bridge_remove_void(void *bridge)
> +{
> + drm_bridge_remove(bridge);
> +}
> +
> +/**
> + * devm_drm_bridge_add - devm managed version of drm_bridge_add()
> + *
> + * @dev: device to tie the bridge lifetime to
> + * @bridge: bridge control structure
> + *
> + * This is the managed version of drm_bridge_add() which automatically
> + * calls drm_bridge_remove() when @dev is unbound.
> + *
> + * Return: 0 if no error or negative error code.
> + */
> +int devm_drm_bridge_add(struct device *dev, struct drm_bridge *bridge)
> +{
> + drm_bridge_add(bridge);
> + return devm_add_action_or_reset(dev, drm_bridge_remove_void, bridge);
> +}
> +EXPORT_SYMBOL(devm_drm_bridge_add);
> +
> /**
> * drm_bridge_remove - remove the given bridge from the global bridge list
> *
> diff --git a/include/drm/drm_bridge.h b/include/drm/drm_bridge.h
> index f27b4060faa2..42aec8612f37 100644
> --- a/include/drm/drm_bridge.h
> +++ b/include/drm/drm_bridge.h
> @@ -796,6 +796,7 @@ drm_priv_to_bridge(struct drm_private_obj *priv)
> }
>
> void drm_bridge_add(struct drm_bridge *bridge);
> +int devm_drm_bridge_add(struct device *dev, struct drm_bridge *bridge);
> void drm_bridge_remove(struct drm_bridge *bridge);
> int drm_bridge_attach(struct drm_encoder *encoder, struct drm_bridge *bridge,
> struct drm_bridge *previous,
> --
> 2.36.0.550.gb090851708-goog
>
--
With best wishes
Dmitry
[PATCH v3 3/4] drm/bridge: Add devm_drm_bridge_add()
This adds a devm managed version of drm_bridge_add(). Like other
"devm" function listed in drm_bridge.h, this function takes an
explicit "dev" to use for the lifetime management. A few notes:
* In general we have a "struct device" for bridges that makes a good
candidate for where the lifetime matches exactly what we want.
* The "bridge->dev->dev" device appears to be the encoder
device. That's not the right device to use for lifetime management.
Suggested-by: Dmitry Baryshkov
Signed-off-by: Douglas Anderson
---
Changes in v3:
- Patch ("drm/bridge: Add devm_drm_bridge_add()") new for v3.
drivers/gpu/drm/drm_bridge.c | 23 +++
include/drm/drm_bridge.h | 1 +
2 files changed, 24 insertions(+)
diff --git a/drivers/gpu/drm/drm_bridge.c b/drivers/gpu/drm/drm_bridge.c
index c96847fc0ebc..e275b4ca344b 100644
--- a/drivers/gpu/drm/drm_bridge.c
+++ b/drivers/gpu/drm/drm_bridge.c
@@ -170,6 +170,29 @@ void drm_bridge_add(struct drm_bridge *bridge)
}
EXPORT_SYMBOL(drm_bridge_add);
+static void drm_bridge_remove_void(void *bridge)
+{
+ drm_bridge_remove(bridge);
+}
+
+/**
+ * devm_drm_bridge_add - devm managed version of drm_bridge_add()
+ *
+ * @dev: device to tie the bridge lifetime to
+ * @bridge: bridge control structure
+ *
+ * This is the managed version of drm_bridge_add() which automatically
+ * calls drm_bridge_remove() when @dev is unbound.
+ *
+ * Return: 0 if no error or negative error code.
+ */
+int devm_drm_bridge_add(struct device *dev, struct drm_bridge *bridge)
+{
+ drm_bridge_add(bridge);
+ return devm_add_action_or_reset(dev, drm_bridge_remove_void, bridge);
+}
+EXPORT_SYMBOL(devm_drm_bridge_add);
+
/**
* drm_bridge_remove - remove the given bridge from the global bridge list
*
diff --git a/include/drm/drm_bridge.h b/include/drm/drm_bridge.h
index f27b4060faa2..42aec8612f37 100644
--- a/include/drm/drm_bridge.h
+++ b/include/drm/drm_bridge.h
@@ -796,6 +796,7 @@ drm_priv_to_bridge(struct drm_private_obj *priv)
}
void drm_bridge_add(struct drm_bridge *bridge);
+int devm_drm_bridge_add(struct device *dev, struct drm_bridge *bridge);
void drm_bridge_remove(struct drm_bridge *bridge);
int drm_bridge_attach(struct drm_encoder *encoder, struct drm_bridge *bridge,
struct drm_bridge *previous,
--
2.36.0.550.gb090851708-goog
