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 <ti...@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 <threeear...@gmail.com>
Reported-by: syzbot+e4c8abb920efa77ba...@syzkaller.appspotmail.com
Cc: <sta...@vger.kernel.org>
Signed-off-by: Takashi Iwai <ti...@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);
--
2.18.0
