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

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Message-ID: <92a4e5e5-33ca-7b39-16c0-82c7fb742d18@i-love.sakura.ne.jp>
Date:   Wed, 13 Mar 2019 06:11:18 +0900
From:   Tetsuo Handa <penguin-kernel@...ove.sakura.ne.jp>
To:     Dmitry Vyukov <dvyukov@...gle.com>
Cc:     syzbot <syzbot+1505c80c74256c6118a5@...kaller.appspotmail.com>,
        syzkaller-bugs <syzkaller-bugs@...glegroups.com>,
        Al Viro <viro@...iv.linux.org.uk>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: INFO: rcu detected stall in sys_sendfile64 (2)

On 2019/03/13 2:15, Dmitry Vyukov wrote:
>> Also, this bisection is finding multiple different crash patterns, which
>> suggests that the crashed tests are not giving correct feedback to syzbot.
> 
> Treating different crashes as just "crash" is intended. Kernel bugs
> can manifest in very different ways.
> Want fun, search for "bpf: sockhash, disallow bpf_tcp_close and update
> in parallel" in  https://syzkaller.appspot.com/?fixed=upstream
> It lead to 50+ different failure modes.
> 

But syzbot already found a rather simple C reproducer
( https://syzkaller.appspot.com/text?tag=ReproC&x=116fc7a8c00000 ) for this bug.
Was this reproducer used for bisection? I guess that if this reproducer was used,
syzbot did not hit "WARNING: ODEBUG bug in netdev_freemem" cases.

Also, humans can sometimes find more simpler C reproducers from syzbot provided
reproducers. It would be nice if syzbot can accept and use a user defined C
reproducer for testing.