linux/include
Pierre-Louis Bossart b450b87847
ASoC: core: don't increase component module refcount unconditionally
The ASoC core has for the longest time increased the module reference
counts, even before the transition to the component model. This is
probably fine on most platforms, but it introduces a deadlock case on
Intel devices with the Skylake and SOF drivers which cannot be removed
due to their reference counts being modified by the core.

In these 2 cases, the PCI or ACPI driver .probe creates a platform
device to let the machine driver .probe register the audio
card. Conversely the PCI or ACPI driver .remove will unregister the
platform device which results in the card being removed by the machine
driver .remove.

With ascii art, this can be represented as

modprobe
snd_soc_skl/
soc-pci-dev/sof-acpci-dev  ----------> pci/acpi probe
       ^                                    |
       |                     ---------------|
       |                    |               |
       |                    V               V
    increase            register        register machine
    refcount            component       platform_device
       ^                                    |
       |                                    |
       |                                    V
    component <----   register card  <---- probe
    probe

The issue is that by playing with the component's module reference
counts during the card registration, it's no longer possible to remove
the module which controls the component. This can be shown, e.g. with
the following error:

root@plb-XPS-13-9350:~# lsmod | grep snd_soc_skl
snd_soc_skl           110592  1

root@plb-XPS-13-9350:~# rmmod snd_soc_skl
rmmod: ERROR: Module snd_soc_skl is in use

Increasing the reference count during the component probe is not
useful. If the PCI/ACPI module is removed, the card will be removed
anyway.

To avoid breaking existing platforms and allowing Intel platforms to
safely deal with module load/unload cases, this patch introduces a
flag which needs to be set during the component initialization. This
is a strictly opt-in capability that should only be used when the
handling of the component module does not require a reference count
increase to prevent removal during use.

Note that this solution is not directly applicable to the legacy
Atom/SST driver, which uses a different device hierarchy. There are
however additional refcount issues which prevent the ACPI driver from
being removed. This is a different issue which would need a different
patch.

Signed-off-by: Pierre-Louis Bossart <pierre-louis.bossart@linux.intel.com>
Signed-off-by: Mark Brown <broonie@kernel.org>
2019-02-08 18:00:20 +00:00
..
acpi Merge branch 'x86-cleanups-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip 2018-12-26 17:03:51 -08:00
asm-generic Merge branch 'akpm' (patches from Andrew) 2019-01-05 09:16:18 -08:00
clocksource
crypto crypto: skcipher - remove remnants of internal IV generators 2018-12-23 11:52:45 +08:00
drm Merge tag 'drm-intel-fixes-2019-01-11' of git://anongit.freedesktop.org/drm/drm-intel into drm-fixes 2019-01-11 10:26:21 +01:00
dt-bindings dt-bindings: reset: meson-axg: fix SPDX license id 2019-01-16 12:50:27 -06:00
keys
kvm
linux gpiolib: acpi: Introduce ACPI_GPIO_QUIRK_ONLY_GPIOIO 2019-02-08 17:29:51 +00:00
math-emu
media media fixes for v4.20-rc8 2018-12-25 13:11:30 -08:00
memory
misc
net ax25: fix possible use-after-free 2019-01-23 11:18:00 -08:00
pcmcia
ras
rdma IB/core: uverbs copy to struct or zero helper 2018-12-20 15:18:18 -07:00
scsi 4.21 merge window pull request 2018-12-28 14:57:10 -08:00
soc ARM: SoC driver updates 2018-12-31 17:32:35 -08:00
sound ASoC: core: don't increase component module refcount unconditionally 2019-02-08 18:00:20 +00:00
target
trace afs: Fix race in async call refcounting 2019-01-17 15:17:28 +00:00
uapi Merge branch 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/dtor/input 2019-01-27 09:07:03 -08:00
video
xen arm64/xen: fix xen-swiotlb cache flushing 2019-01-23 22:14:56 +01:00