On Tue, 14 Aug 2018 16:20:02 +0200, syzbot wrote: > > Hello, > > syzbot found the following crash on: > > HEAD commit: 4e8b38549b50 Add linux-next specific files for 20180814 > git tree: linux-next > console output: https://syzkaller.appspot.com/x/log.txt?x=11f5e78c400000 > kernel config: https://syzkaller.appspot.com/x/.config?x=18edf0289d1b5ab > dashboard link: https://syzkaller.appspot.com/bug?extid=ec5f605c91812d200367 > compiler: gcc (GCC) 8.0.1 20180413 (experimental) > syzkaller repro:https://syzkaller.appspot.com/x/repro.syz?x=12f8c6d2400000 > C reproducer: https://syzkaller.appspot.com/x/repro.c?x=16976b72400000 > > IMPORTANT: if you fix the bug, please add the following tag to the commit: > Reported-by: syzbot+ec5f605c91812d200367@xxxxxxxxxxxxxxxxxxxxxxxxx > > WARNING: CPU: 1 PID: 1691 at sound/core/rawmidi.c:1170 > __snd_rawmidi_transmit_ack+0x263/0x2f0 sound/core/rawmidi.c:1170 This seems to be a bad side-effect by the code change along with the offloading the virmidi work. I'm going to queue the fix below. thanks, Takashi -- 8< -- From: Takashi Iwai <tiwai@xxxxxxx> Subject: [PATCH] ALSA: seq: virmidi: Fix discarding the unsubscribed output The recent change to move the virmidi output processing to a work slightly modified the code to discard the unsubscribed outputs so that it works without a temporary buffer. However, this is actually buggy, and may spew a kernel warning due to the unexpected call of snd_rawmidi_transmit_ack(), as triggered by syzbot. This patch takes back to the original code in that part, use a temporary buffer and simply repeat snd_rawmidi_transmit(), in order to address the regression. Fixes: f7debfe54090 ("ALSA: seq: virmidi: Offload the output event processing") Reported-by: syzbot+ec5f605c91812d200367@xxxxxxxxxxxxxxxxxxxxxxxxx Signed-off-by: Takashi Iwai <tiwai@xxxxxxx> --- sound/core/seq/seq_virmidi.c | 5 +++-- 1 file changed, 3 insertions(+), 2 deletions(-) diff --git a/sound/core/seq/seq_virmidi.c b/sound/core/seq/seq_virmidi.c index a2f1c6b58693..cb988efd1ed0 100644 --- a/sound/core/seq/seq_virmidi.c +++ b/sound/core/seq/seq_virmidi.c @@ -149,8 +149,9 @@ static void snd_vmidi_output_work(struct work_struct *work) /* discard the outputs in dispatch mode unless subscribed */ if (vmidi->seq_mode == SNDRV_VIRMIDI_SEQ_DISPATCH && !(vmidi->rdev->flags & SNDRV_VIRMIDI_SUBSCRIBE)) { - while (!snd_rawmidi_transmit_empty(substream)) - snd_rawmidi_transmit_ack(substream, 1); + char buf[32]; + while (snd_rawmidi_transmit(substream, buf, sizeof(buf)) > 0) + ; /* ignored */ return; } -- 2.18.0 _______________________________________________ Alsa-devel mailing list Alsa-devel@xxxxxxxxxxxxxxxx http://mailman.alsa-project.org/mailman/listinfo/alsa-devel
