[alsa-devel] INFO: rcu detected stall in snd_pcm_oss_write3 (2)

[Dmitry Vyukov]

On Sat, Apr 7, 2018 at 11:56 AM, Takashi Iwai <tiwai at suse.de> wrote:
> On Fri, 06 Apr 2018 23:14:01 +0200,
> syzbot wrote:
>>
>> syzbot has found reproducer for the following crash on upstream commit
>> 38c23685b273cfb4ccf31a199feccce3bdcb5d83 (Fri Apr 6 04:29:35 2018 +0000)
>> Merge tag 'armsoc-drivers' of
>> git://git.kernel.org/pub/scm/linux/kernel/git/arm/arm-soc
>> syzbot dashboard link:
>> https://syzkaller.appspot.com/bug?extid=150189c103427d31a053
>>
>> So far this crash happened 15 times on upstream.
>> C reproducer: https://syzkaller.appspot.com/x/repro.c?id=5405588854931456
>> syzkaller reproducer:
>> https://syzkaller.appspot.com/x/repro.syz?id=5561439796330496
>> Raw console output:
>> https://syzkaller.appspot.com/x/log.txt?id=5697900571000832
>> Kernel config:
>> https://syzkaller.appspot.com/x/.config?id=-5813481738265533882
>> compiler: gcc (GCC) 8.0.1 20180301 (experimental)
>
> Thanks to the reproducer, I could spot out now.
> Below is the patch (which was submitted as well).

Great!

There are 3 more recent stalls in sound, does this fix them as well?

https://groups.google.com/forum/#!msg/syzkaller-bugs/MGfk8WH3O6k/ja2xKpdcCAAJ
https://groups.google.com/forum/#!msg/syzkaller-bugs/74HglwU94go/T89ohzlYCAAJ
https://groups.google.com/forum/#!msg/syzkaller-bugs/D2xWV7WTRDk/5y2kZyBICAAJ


> thanks,
>
> Takashi
>
> -- 8< --
> From: Takashi Iwai <tiwai at suse.de>
> Subject: [PATCH] ALSA: pcm: Fix endless loop for XRUN recovery in OSS
>  emulation
>
> The commit 02a5d6925cd3 ("ALSA: pcm: Avoid potential races between OSS
> ioctls and read/write") split the PCM preparation code to a locked
> version, and it added a sanity check of runtime->oss.prepare flag
> along with the change.  This leaded to an endless loop when the stream
> gets XRUN: namely, snd_pcm_oss_write3() and co call
> snd_pcm_oss_prepare() without setting runtime->oss.prepare flag and
> the loop continues until the PCM state reaches to another one.
>
> As the function is supposed to execute the preparation
> unconditionally, drop the invalid state check there.
>
> The bug was triggered by syzkaller.
>
> Fixes: 02a5d6925cd3 ("ALSA: pcm: Avoid potential races between OSS ioctls and read/write")
> Reported-by: syzbot+7e3f31a52646f939c052 at syzkaller.appspotmail.com
> Reported-by: syzbot+4f2016cf5185da7759dc at syzkaller.appspotmail.com
> Cc: <stable at vger.kernel.org>
> Signed-off-by: Takashi Iwai <tiwai at suse.de>
> ---
>  sound/core/oss/pcm_oss.c | 3 +--
>  1 file changed, 1 insertion(+), 2 deletions(-)
>
> diff --git a/sound/core/oss/pcm_oss.c b/sound/core/oss/pcm_oss.c
> index 481ab0e94ffa..727647755aab 100644
> --- a/sound/core/oss/pcm_oss.c
> +++ b/sound/core/oss/pcm_oss.c
> @@ -1128,13 +1128,12 @@ static int snd_pcm_oss_get_active_substream(struct snd_pcm_oss_file *pcm_oss_fil
>  }
>
>  /* call with params_lock held */
> +/* NOTE: this doesn't care whether runtime->oss.prepare is set or not */
>  static int snd_pcm_oss_prepare(struct snd_pcm_substream *substream)
>  {
>         int err;
>         struct snd_pcm_runtime *runtime = substream->runtime;
>
> -       if (!runtime->oss.prepare)
> -               return 0;
>         err = snd_pcm_kernel_ioctl(substream, SNDRV_PCM_IOCTL_PREPARE, NULL);
>         if (err < 0) {
>                 pcm_dbg(substream->pcm,
> --
> 2.16.3
>