On 28. 07. 22 14:59, Takashi Iwai wrote:
Currently the call of kill_fasync() from an interrupt handler might
lead to potential spin deadlocks, as spotted by syzkaller.
Unfortunately, it's not so trivial to fix this lock chain as it's
involved with the tasklist_lock that is touched in allover places.
As a temporary workaround, this patch provides the way to defer the
async signal notification in a work. The new helper functions,
snd_fasync_helper() and snd_kill_faync() are replacements for
fasync_helper() and kill_fasync(), respectively. In addition,
snd_fasync_free() needs to be called at the destructor of the relevant
file object.
Signed-off-by: Takashi Iwai <tiwai@xxxxxxx>
...
+void snd_kill_fasync(struct snd_fasync *fasync, int signal, int poll)
+{
+ unsigned long flags;
+
+ if (!fasync || !fasync->on)
+ return;
+ spin_lock_irqsave(&snd_fasync_lock, flags);
+ fasync->signal = signal;
+ fasync->poll = poll;
+ list_move(&fasync->list, &snd_fasync_list);
+ schedule_work(&snd_fasync_work);
+ spin_unlock_irqrestore(&snd_fasync_lock, flags);
+}
The schedule_work() may be called outside the spinlock - it calls
queue_work_on() / __queue_work() which has already own protection for the
concurrent execution.
Jaroslav
--
Jaroslav Kysela <perex@xxxxxxxx>
Linux Sound Maintainer; ALSA Project; Red Hat, Inc.
