From: Norbert Szetei Date: Tue, 28 Jul 2026 12:50:01 +0000 (+0200) Subject: ALSA: pcm: wake linked drain waiters on unlink X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=f495b6c4c8594122918552c9be2b51eb71647cd9;p=thirdparty%2Flinux.git ALSA: pcm: wake linked drain waiters on unlink snd_pcm_drain() on a linked stream parks an on-stack wait entry on the drained peer's runtime->sleep, and after schedule_timeout() removes it only if that peer is still found in the caller's group. If group membership changes during the wait and the sleep ends by signal or timeout (so autoremove_wake_function() does not run), finish_wait() is skipped and snd_pcm_drain() returns with the entry still queued on that stream's sleep list; a later wake_up() then walks a freed stack frame. This is reachable by unlinking either the drained or the draining stream. Unlike the close path (snd_pcm_drop() -> snd_pcm_post_stop()), snd_pcm_unlink() never wakes the sleep queues. Wake every group member under the group lock before the membership change, so a linked drainer is released and drops its entry while the streams are still grouped. The window was opened when snd_pcm_link_rwsem stopped being held across the wait and the removal became conditional on group membership (see Fixes). The later switch to finish_wait() kept that conditional removal, so the signal/timeout case remained. Fixes: f57f3df03a8e ("ALSA: pcm: More fine-grained PCM link locking") Cc: stable@vger.kernel.org Assisted-by: Claude:claude-opus-5 Signed-off-by: Norbert Szetei Link: https://patch.msgid.link/A0705100-D10B-4286-9980-0142ABEEAD51@doyensec.com Signed-off-by: Takashi Iwai --- diff --git a/sound/core/pcm_native.c b/sound/core/pcm_native.c index 7dc0060617f1..c9d0c2bb55b2 100644 --- a/sound/core/pcm_native.c +++ b/sound/core/pcm_native.c @@ -2367,6 +2367,7 @@ static void relink_to_local(struct snd_pcm_substream *substream) static int snd_pcm_unlink(struct snd_pcm_substream *substream) { + struct snd_pcm_substream *s; struct snd_pcm_group *group; bool nonatomic = substream->pcm->nonatomic; bool do_free = false; @@ -2379,6 +2380,12 @@ static int snd_pcm_unlink(struct snd_pcm_substream *substream) group = substream->group; snd_pcm_group_lock_irq(group, nonatomic); + /* release drain waiters before changing membership, else snd_pcm_drain() + * leaves its on-stack wait entry queued on a member's sleep list + */ + snd_pcm_group_for_each_entry(s, substream) + wake_up(&s->runtime->sleep); + relink_to_local(substream); refcount_dec(&group->refs);