[Intel-gfx] [PATCH v2] component: do not leave master devres group open after bind

[Greg KH]

On Wed, Sep 22, 2021 at 11:54:32AM +0300, Kai Vehmanen wrote:
> In current code, the devres group for aggregate master is left open
> after call to component_master_add_*(). This leads to problems when the
> master does further managed allocations on its own. When any
> participating driver calls component_del(), this leads to immediate
> release of resources.
> 
> This came up when investigating a page fault occurring with i915 DRM
> driver unbind with 5.15-rc1 kernel. The following sequence occurs:
> 
>  i915_pci_remove()
>    -> intel_display_driver_unregister()
>      -> i915_audio_component_cleanup()
>        -> component_del()
>          -> component.c:take_down_master()
>            -> hdac_component_master_unbind() [via master->ops->unbind()]
>            -> devres_release_group(master->parent, NULL)
> 
> With older kernels this has not caused issues, but with audio driver
> moving to use managed interfaces for more of its allocations, this no
> longer works. Devres log shows following to occur:
> 
> component_master_add_with_match()
> [  126.886032] snd_hda_intel 0000:00:1f.3: DEVRES ADD 00000000323ccdc5 devm_component_match_release (24 bytes)
> [  126.886045] snd_hda_intel 0000:00:1f.3: DEVRES ADD 00000000865cdb29 grp< (0 bytes)
> [  126.886049] snd_hda_intel 0000:00:1f.3: DEVRES ADD 000000001b480725 grp< (0 bytes)
> 
> audio driver completes its PCI probe()
> [  126.892238] snd_hda_intel 0000:00:1f.3: DEVRES ADD 000000001b480725 pcim_iomap_release (48 bytes)
> 
> component_del() called() at DRM/i915 unbind()
> [  137.579422] i915 0000:00:02.0: DEVRES REL 00000000ef44c293 grp< (0 bytes)
> [  137.579445] snd_hda_intel 0000:00:1f.3: DEVRES REL 00000000865cdb29 grp< (0 bytes)
> [  137.579458] snd_hda_intel 0000:00:1f.3: DEVRES REL 000000001b480725 pcim_iomap_release (48 bytes)
> 
> So the "devres_release_group(master->parent, NULL)" ends up freeing the
> pcim_iomap allocation. Upon next runtime resume, the audio driver will
> cause a page fault as the iomap alloc was released without the driver
> knowing about it.
> 
> Fix this issue by using the "struct master" pointer as identifier for
> the devres group, and by closing the devres group after
> the master->ops->bind() call is done. This allows devres allocations
> done by the driver acting as master to be isolated from the binding state
> of the aggregate driver. This modifies the logic originally introduced in
> commit 9e1ccb4a7700 ("drivers/base: fix devres handling for master device")
> 
> BugLink: https://gitlab.freedesktop.org/drm/intel/-/issues/4136
> Signed-off-by: Kai Vehmanen <kai.vehmanen at linux.intel.com>
> Acked-by: Imre Deak <imre.deak at intel.com>
> Acked-by: Russell King (Oracle) <rmk+kernel at armlinux.org.uk>
> ---
>  drivers/base/component.c | 5 +++--
>  1 file changed, 3 insertions(+), 2 deletions(-)

What commit does this "fix:"?  And does it need to go to stable
kernel(s)?

thanks,

greg k-h