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