3.16.62-rc1 review patch. If anyone has any objections, please let me know.
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From: Takashi Iwai tiwai@suse.de
commit 50e9ffb1996a5d11ff5040a266585bad4ceeca0a upstream.
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 Signed-off-by: Takashi Iwai tiwai@suse.de Signed-off-by: Ben Hutchings ben@decadent.org.uk --- sound/core/seq/seq_virmidi.c | 10 ++++++++++ 1 file changed, 10 insertions(+)
--- a/sound/core/seq/seq_virmidi.c +++ b/sound/core/seq/seq_virmidi.c @@ -163,6 +163,7 @@ static void snd_virmidi_output_trigger(s 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(s 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);