Searched hist:a3933186 (Results 1 – 1 of 1) sorted by relevance
/openbmc/linux/sound/core/ |
H A D | timer.c | a3933186 Wed Oct 30 16:42:57 CDT 2019 Takashi Iwai <tiwai@suse.de> ALSA: timer: Fix mutex deadlock at releasing card
When a card is disconnected while in use, the system waits until all opened files are closed then releases the card. This is done via put_device() of the card device in each device release code.
The recently reported mutex deadlock bug happens in this code path; snd_timer_close() for the timer device deals with the global register_mutex and it calls put_device() there. When this timer device is the last one, the card gets freed and it eventually calls snd_timer_free(), which has again the protection with the global register_mutex -- boom.
Basically put_device() call itself is race-free, so a relative simple workaround is to move this put_device() call out of the mutex. For achieving that, in this patch, snd_timer_close_locked() got a new argument to store the card device pointer in return, and each caller invokes put_device() with the returned object after the mutex unlock.
Reported-and-tested-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com> Cc: <stable@vger.kernel.org> Signed-off-by: Takashi Iwai <tiwai@suse.de> a3933186 Wed Oct 30 16:42:57 CDT 2019 Takashi Iwai <tiwai@suse.de> ALSA: timer: Fix mutex deadlock at releasing card When a card is disconnected while in use, the system waits until all opened files are closed then releases the card. This is done via put_device() of the card device in each device release code. The recently reported mutex deadlock bug happens in this code path; snd_timer_close() for the timer device deals with the global register_mutex and it calls put_device() there. When this timer device is the last one, the card gets freed and it eventually calls snd_timer_free(), which has again the protection with the global register_mutex -- boom. Basically put_device() call itself is race-free, so a relative simple workaround is to move this put_device() call out of the mutex. For achieving that, in this patch, snd_timer_close_locked() got a new argument to store the card device pointer in return, and each caller invokes put_device() with the returned object after the mutex unlock. Reported-and-tested-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com> Cc: <stable@vger.kernel.org> Signed-off-by: Takashi Iwai <tiwai@suse.de>
|