linux-kernel - Re: INFO: rcu detected stall in io_playback

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Date:   Mon, 09 Apr 2018 14:59:38 +0200
From:   Takashi Iwai <tiwai@...e.de>
To:     "Tetsuo Handa" <penguin-kernel@...ove.SAKURA.ne.jp>
Cc:     <dvyukov@...gle.com>, <alsa-devel@...a-project.org>,
        <syzkaller-bugs@...glegroups.com>, <mingo@...nel.org>,
        <dan.carpenter@...cle.com>, <perex@...ex.cz>,
        <o-takashi@...amocchi.jp>,
        <syzbot+4f2016cf5185da7759dc@...kaller.appspotmail.com>,
        <linux-kernel@...r.kernel.org>, <viro@...iv.linux.org.uk>
Subject: Re: INFO: rcu detected stall in io_playback_transfer

On Sun, 08 Apr 2018 15:26:21 +0200,
Tetsuo Handa wrote:
> 
> Dmitry Vyukov wrote:
> > Takashi has already fixed this. See this thread:
> > https://groups.google.com/forum/#!searchin/syzkaller-bugs/%22INFO$3A$20rcu$20detected$20stall$20in$20snd_pcm_oss_write3$20(2)%22%7Csort:date/syzkaller-bugs/D2xWV7WTRDk/sCw_gImmCAAJ
> 
> Yes, I noticed it just before I post this. But the reason I posted this anyway
> is that I feel that there is some other bug revealed by this reproducer.
> How can Takashi' patch explain my observation (with linux-next-20180406) ?

The bug is triggered by any buffer underrun of a PCM stream via OSS
emulation, so the condition can vary in any form.  That is, if an app
doesn't give the enough amount in time, the PCM goes to XRUN state.
Then at closing, the driver tries to sync the pending data and hits
the bug.


Takashi