From ff80185e7b7b547a0911fcfc8aefc61c3e8304d7 Mon Sep 17 00:00:00 2001 From: Takashi Iwai Date: Fri, 10 May 2024 12:14:23 +0200 Subject: [PATCH] ALSA: Fix deadlocks with kctl removals at disconnection commit 87988a534d8e12f2e6fc01fe63e6c1925dc5307c upstream. In snd_card_disconnect(), we set card->shutdown flag at the beginning, call callbacks and do sync for card->power_ref_sleep waiters at the end. The callback may delete a kctl element, and this can lead to a deadlock when the device was in the suspended state. Namely: * A process waits for the power up at snd_power_ref_and_wait() in snd_ctl_info() or read/write() inside card->controls_rwsem. * The system gets disconnected meanwhile, and the driver tries to delete a kctl via snd_ctl_remove*(); it tries to take card->controls_rwsem again, but this is already locked by the above. Since the sleeper isn't woken up, this deadlocks. An easy fix is to wake up sleepers before processing the driver disconnect callbacks but right after setting the card->shutdown flag. Then all sleepers will abort immediately, and the code flows again. So, basically this patch moves the wait_event() call at the right timing. While we're at it, just to be sure, call wait_event_all() instead of wait_event(), although we don't use exclusive events on this queue for now. Link: https://bugzilla.kernel.org/show_bug.cgi?id=218816 Cc: Reviewed-by: Jaroslav Kysela Link: https://lore.kernel.org/r/20240510101424.6279-1-tiwai@suse.de Signed-off-by: Takashi Iwai Signed-off-by: Greg Kroah-Hartman --- sound/core/init.c | 9 ++++++++- 1 file changed, 8 insertions(+), 1 deletion(-) diff --git a/sound/core/init.c b/sound/core/init.c index ab7853924fd3..088f4f1874b3 100644 --- a/sound/core/init.c +++ b/sound/core/init.c @@ -508,6 +508,14 @@ int snd_card_disconnect(struct snd_card *card) } spin_unlock(&card->files_lock); +#ifdef CONFIG_PM + /* wake up sleepers here before other callbacks for avoiding potential + * deadlocks with other locks (e.g. in kctls); + * then this notifies the shutdown and sleepers would abort immediately + */ + wake_up_all(&card->power_sleep); +#endif + /* notify all connected devices about disconnection */ /* at this point, they cannot respond to any calls except release() */ @@ -535,7 +543,6 @@ int snd_card_disconnect(struct snd_card *card) mutex_unlock(&snd_card_mutex); #ifdef CONFIG_PM - wake_up(&card->power_sleep); snd_power_sync_ref(card); #endif return 0;