Re: INFO: task hung in fsnotify_connector_destroy_workfn (2)

[Dmitry Vyukov]

On Mon, Sep 24, 2018 at 3:19 PM, Jiri Kosina <jikos@xxxxxxxxxx> wrote:
> On Sun, 16 Sep 2018, Amir Goldstein wrote:
>
>> > > syzbot found the following crash on:
>> > >
>> > > HEAD commit:    11da3a7f84f1 Linux 4.19-rc3
>> > > git tree:       upstream
>> > > console output: https://syzkaller.appspot.com/x/log.txt?x=141ffbca400000
>> > > kernel config:  https://syzkaller.appspot.com/x/.config?x=9917ff4b798e1a1e
>> > > dashboard link: https://syzkaller.appspot.com/bug?extid=6fb572170402d311dd39
>> > > compiler:       gcc (GCC) 8.0.1 20180413 (experimental)
>> > > syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=136a60ae400000
>> > >
>> > > IMPORTANT: if you fix the bug, please add the following tag to the commit:
>> > > Reported-by: syzbot+6fb572170402d311dd39@xxxxxxxxxxxxxxxxxxxxxxxxx
>> > >
>> >
>> > Since it kept printk()ing for at least 93 seconds, it might have kept for 150 seconds.
>> >
>> > [  174.614333] hid-generic 0000:0000:0000.0003: unknown main item tag 0x0
>> > [  268.196102] INFO: task kworker/u4:1:23 blocked for more than 140 seconds.
>> >
>> > Since the reproducer is simple, this might be lockup due to continuous printk().
>> > If syzbot can reliably reproduce this problem using the reproducer, try
>> > ratelimiting printk().
>>
>> Right.. and I was able to reproduce after setting CONFIG_HID_GENERIC=y
>> but unless I am missing something, the core problem doesn't seem related to
>> fsnotify and $SUBJECT, so CCing HID maintainer.
>
> Alright, so you're basically triggering a never-ending flow of kmsgs being
> printed out from HID parser due to doing crazy things with the parser, and
> that causes the issues for the kworker trying to flush them out.
>
> I guess the patch below fixes it, however the kworker should not really be
> blocked by this I think ... adding a few more printk folks to double-check
> why the kworker would get stuck due to massive printk() flood.


The task hanged in synchronize_rcu(). I think any infinite loop
(whether it prints or not) can cause this.


> diff --git a/include/linux/hid.h b/include/linux/hid.h
> index d44a78362942..b81332fe85a4 100644
> --- a/include/linux/hid.h
> +++ b/include/linux/hid.h
> @@ -1157,22 +1157,22 @@ do {                                                                    \
>  } while (0)
>
>  #define hid_printk(level, hid, fmt, arg...)            \
> -       dev_printk(level, &(hid)->dev, fmt, ##arg)
> +       dev_printk_ratelimited(level, &(hid)->dev, fmt, ##arg)
>  #define hid_emerg(hid, fmt, arg...)                    \
> -       dev_emerg(&(hid)->dev, fmt, ##arg)
> +       dev_emerg_ratelimited(&(hid)->dev, fmt, ##arg)
>  #define hid_crit(hid, fmt, arg...)                     \
> -       dev_crit(&(hid)->dev, fmt, ##arg)
> +       dev_crit_ratelimited(&(hid)->dev, fmt, ##arg)
>  #define hid_alert(hid, fmt, arg...)                    \
> -       dev_alert(&(hid)->dev, fmt, ##arg)
> +       dev_alert_ratelimited(&(hid)->dev, fmt, ##arg)
>  #define hid_err(hid, fmt, arg...)                      \
> -       dev_err(&(hid)->dev, fmt, ##arg)
> +       dev_err_ratelimited(&(hid)->dev, fmt, ##arg)
>  #define hid_notice(hid, fmt, arg...)                   \
> -       dev_notice(&(hid)->dev, fmt, ##arg)
> +       dev_notice_ratelimited(&(hid)->dev, fmt, ##arg)
>  #define hid_warn(hid, fmt, arg...)                     \
> -       dev_warn(&(hid)->dev, fmt, ##arg)
> +       dev_warn_ratelimited(&(hid)->dev, fmt, ##arg)
>  #define hid_info(hid, fmt, arg...)                     \
> -       dev_info(&(hid)->dev, fmt, ##arg)
> +       dev_info_ratelimited(&(hid)->dev, fmt, ##arg)
>  #define hid_dbg(hid, fmt, arg...)                      \
> -       dev_dbg(&(hid)->dev, fmt, ##arg)
> +       dev_dbg_ratelimited(&(hid)->dev, fmt, ##arg)
>
>  #endif
>
> --
> Jiri Kosina
> SUSE Labs
>
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