Hello,
My static analysis tool reports a possible deadlock in the sound driver
in Linux 5.10:
snd_card_disconnect_sync()
spin_lock_irq(&card->files_lock); --> Line 461 (Lock A)
wait_event_lock_irq(card->remove_sleep, ...); --> Line 462 (Wait X)
spin_unlock_irq(&card->files_lock); --> Line 465 (Unlock A)
snd_hwdep_release()
mutex_lock(&hw->open_mutex); --> Line 152 (Lock B)
mutex_unlock(&hw->open_mutex); --> Line 157 (Unlock B)
snd_card_file_remove()
wake_up_all(&card->remove_sleep); --> Line 976 (Wake X)
snd_hwdep_open()
mutex_lock(&hw->open_mutex); --> Line 95 (Lock B)
snd_card_file_add()
spin_lock(&card->files_lock); --> Line 932 (Lock A)
spin_unlock(&card->files_lock); --> Line 940 (Unlock A)
mutex_unlock(&hw->open_mutex); --> Line 139 (Unlock B)
When snd_card_disconnect_sync() is executed, "Wait X" is performed by
holding "Lock A". If snd_hwdep_open() is executed at this time, it holds
"Lock B" and then waits for acquiring "Lock A". If snd_hwdep_release()
is executed at this time, it waits for acquiring "Lock B", and thus
"Wake X" cannot be performed to wake up "Wait X" in
snd_card_disconnect_sync(), causing a possible deadlock.
I am not quite sure whether this possible problem is real and how to fix
it if it is real.
Any feedback would be appreciated, thanks :)
Best wishes,
Jia-Ju Bai
