On Fri, 27 Jul 2018 06:13:22 +0200, Dae R. Jeong wrote:
I tested it and it worked. Thanks a lot!
Good to hear. Below is the final patch with a proper comment (and with syzbot reported-by, too) I'm going to queue to sound.git tree.
thanks,
Takashi
-- 8< --
From: Takashi Iwai tiwai@suse.de Subject: [PATCH v2] ALSA: virmidi: Fix too long output trigger loop
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+e4c8abb920efa77bace9@syzkaller.appspotmail.com Cc: stable@vger.kernel.org Signed-off-by: Takashi Iwai tiwai@suse.de --- sound/core/seq/seq_virmidi.c | 10 ++++++++++ 1 file changed, 10 insertions(+)
diff --git a/sound/core/seq/seq_virmidi.c b/sound/core/seq/seq_virmidi.c index 289ae6bb81d9..8ebbca554e99 100644 --- a/sound/core/seq/seq_virmidi.c +++ b/sound/core/seq/seq_virmidi.c @@ -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);