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Subject: Re: kernel panic: corrupted stack end in wb_workfn
To:     Dmitry Vyukov <dvyukov@google.com>,
        Andrey Ryabinin <aryabinin@virtuozzo.com>
Cc:     syzbot <syzbot+ec1b7575afef85a0e5ca@syzkaller.appspotmail.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        Qian Cai <cai@lca.pw>, David Miller <davem@davemloft.net>,
        guro@fb.com, Johannes Weiner <hannes@cmpxchg.org>,
        Josef Bacik <jbacik@fb.com>,
        Kirill Tkhai <ktkhai@virtuozzo.com>,
        LKML <linux-kernel@vger.kernel.org>,
        Linux-MM <linux-mm@kvack.org>, linux-sctp@vger.kernel.org,
        Mel Gorman <mgorman@techsingularity.net>,
        Michal Hocko <mhocko@suse.com>,
        netdev <netdev@vger.kernel.org>,
        Neil Horman <nhorman@tuxdriver.com>,
        Shakeel Butt <shakeelb@google.com>,
        syzkaller-bugs <syzkaller-bugs@googlegroups.com>,
        Al Viro <viro@zeniv.linux.org.uk>,
        Vladislav Yasevich <vyasevich@gmail.com>,
        Matthew Wilcox <willy@infradead.org>,
        Xin Long <lucien.xin@gmail.com>
References: <000000000000db3d130584506672@google.com>
 <d9e4e36d-1e7a-caaf-f96e-b05592405b5f@virtuozzo.com>
 <CACT4Y+Zj=35t2djhKoq+e1SH3Zu3389Pns7xX6MiMWZ=PFpShA@mail.gmail.com>
From:   Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
Message-ID: <426293c3-bf63-88ad-06fb-83927ab0d7c0@I-love.SAKURA.ne.jp>
Date:   Wed, 20 Mar 2019 19:23:58 +0900
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On 2019/03/20 18:59, Dmitry Vyukov wrote:
>> From bisection log:
>>
>>         testing release v4.17
>>         testing commit 29dcea88779c856c7dc92040a0c01233263101d4 with gcc (GCC) 8.1.0
>>         run #0: crashed: kernel panic: corrupted stack end in wb_workfn
>>         run #1: crashed: kernel panic: corrupted stack end in worker_thread
>>         run #2: crashed: kernel panic: Out of memory and no killable processes...
>>         run #3: crashed: kernel panic: corrupted stack end in wb_workfn
>>         run #4: crashed: kernel panic: corrupted stack end in wb_workfn
>>         run #5: crashed: kernel panic: corrupted stack end in wb_workfn
>>         run #6: crashed: kernel panic: corrupted stack end in wb_workfn
>>         run #7: crashed: kernel panic: corrupted stack end in wb_workfn
>>         run #8: crashed: kernel panic: Out of memory and no killable processes...
>>         run #9: crashed: kernel panic: corrupted stack end in wb_workfn
>>         testing release v4.16
>>         testing commit 0adb32858b0bddf4ada5f364a84ed60b196dbcda with gcc (GCC) 8.1.0
>>         run #0: OK
>>         run #1: OK
>>         run #2: OK
>>         run #3: OK
>>         run #4: OK
>>         run #5: crashed: kernel panic: Out of memory and no killable processes...
>>         run #6: OK
>>         run #7: crashed: kernel panic: Out of memory and no killable processes...
>>         run #8: OK
>>         run #9: OK
>>         testing release v4.15
>>         testing commit d8a5b80568a9cb66810e75b182018e9edb68e8ff with gcc (GCC) 8.1.0
>>         all runs: OK
>>         # git bisect start v4.16 v4.15
>>
>> Why bisect started between 4.16 4.15 instead of 4.17 4.16?
> 
> Because 4.16 was still crashing and 4.15 was not crashing. 4.15..4.16
> looks like the right range, no?

No, syzbot should bisect between 4.16 and 4.17 regarding this bug, for
"Stack corruption" can't manifest as "Out of memory and no killable processes".

"kernel panic: Out of memory and no killable processes..." is completely
unrelated to "kernel panic: corrupted stack end in wb_workfn".