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ALSA: virmidi: Fix too long output trigger loop

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The virmidi output trigger tries to parse the all available bytes and
process sequencer events as much as possible.  In a normal situation,
this is supposed to be relatively short, but a program may give a huge
buffer and it'll take a long time in a single spin lock, which may
eventually lead to a soft lockup.

This patch simply adds a workaround, a cond_resched() call in the loop
if applicable.  A better solution would be to move the event processor
into a work, but let's put a duct-tape quickly at first.

Reported-and-tested-by: Dae R. Jeong <threeearcat@gmail.com>
Reported-by: syzbot+619d9f40141d826b097e@syzkaller.appspotmail.com
Cc: <stable@vger.kernel.org>
Signed-off-by: Takashi Iwai <tiwai@suse.de>
This commit is contained in:
Takashi Iwai 2018-07-26 14:27:59 +02:00
parent 69756930f2
commit 50e9ffb199
1 changed files with 10 additions and 0 deletions
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10
sound/core/seq/seq_virmidi.c
View file

@ -163,6 +163,7 @@ static void snd_virmidi_output_trigger(struct snd_rawmidi_substream *substream,
int count, res;
unsigned char buf[32], *pbuf;
unsigned long flags;
bool check_resched = !in_atomic();
if (up) {
vmidi->trigger = 1;
@ -200,6 +201,15 @@ static void snd_virmidi_output_trigger(struct snd_rawmidi_substream *substream,
vmidi->event.type = SNDRV_SEQ_EVENT_NONE;
}
}
if (!check_resched)
continue;
/* do temporary unlock & cond_resched() for avoiding
* CPU soft lockup, which may happen via a write from
* a huge rawmidi buffer
*/
spin_unlock_irqrestore(&substream->runtime->lock, flags);
cond_resched();
spin_lock_irqsave(&substream->runtime->lock, flags);
}
out:
spin_unlock_irqrestore(&substream->runtime->lock, flags);