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c87761db21
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
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Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.