On Fri, 27 Jul 2018 07:51:04 +0200, Dae R. Jeong wrote:
On Fri, Jul 27, 2018 at 07:20:30AM +0200, Takashi Iwai wrote:
I think there is a mistake on the reported-by tag. The reported-by tag (e4c8abb920ef...) is for WARNING in port_delete. I guess the tag below is correct. Reported-by: syzbot+619d9f40141d826b097e@syzkaller.appspotmail.com Could you please make sure that the reported-by tag is correct?
Indeed, corrected now. Thanks.
By the way, I can't reproduce the crash WARNING in port_delete so far. I feel sad for saying this.. I really want to reproduce the crash and thus, to help to fix the crash. If there is any progress on it, I will let you know immediately.
This looks like a sheer race condition. Thanks for your help in anyway!
Takashi
Best regards, Dae R. Jeong
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);-- 2.18.0