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authorTakashi Iwai <tiwai@suse.de>2018-07-26 15:27:59 +0300
committerTakashi Iwai <tiwai@suse.de>2018-07-27 09:59:25 +0300
commit50e9ffb1996a5d11ff5040a266585bad4ceeca0a (patch)
tree08e78c81cff8ff31ef01923c4ea5436732c4eed2
parent69756930f2de0457d51db7d505a1e4f40e9fd116 (diff)
downloadlinux-50e9ffb1996a5d11ff5040a266585bad4ceeca0a.tar.xz
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+619d9f40141d826b097e@syzkaller.appspotmail.com Cc: <stable@vger.kernel.org> Signed-off-by: Takashi Iwai <tiwai@suse.de>
-rw-r--r--sound/core/seq/seq_virmidi.c10
1 files changed, 10 insertions, 0 deletions
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);