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From:   Dmitry Vyukov <dvyukov@google.com>
Date:   Thu, 21 Mar 2019 10:51:14 +0100
Message-ID: <CACT4Y+Z4yLPRRfRa4GhTDOQkuOsQccAOcBMoD4sgMmYj69ggrg@mail.gmail.com>
Subject: Re: kernel panic: corrupted stack end in wb_workfn
To:     Andrey Ryabinin <aryabinin@virtuozzo.com>
Cc:     Tetsuo Handa <penguin-kernel@i-love.sakura.ne.jp>,
        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>
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On Thu, Mar 21, 2019 at 10:45 AM Dmitry Vyukov <dvyukov@google.com> wrote:
>
> On Wed, Mar 20, 2019 at 2:57 PM Dmitry Vyukov <dvyukov@google.com> wrote:
> >
> > On Wed, Mar 20, 2019 at 2:33 PM Andrey Ryabinin <aryabinin@virtuozzo.com> wrote:
> > >
> > >
> > >
> > > On 3/20/19 1:38 PM, Dmitry Vyukov wrote:
> > > > On Wed, Mar 20, 2019 at 11:24 AM Tetsuo Handa
> > > > <penguin-kernel@i-love.sakura.ne.jp> wrote:
> > > >>
> > > >> 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".
> > > >
> > > >
> > > > Do you think this predicate is possible to code?
> > >
> > > Something like bellow probably would work better than current behavior.
> > >
> > > For starters, is_duplicates() might just compare 'crash' title with 'target_crash' title and its duplicates titles.
> >
> > Lots of bugs (half?) manifest differently. On top of this, titles
> > change as we go back in history. On top of this, if we see a different
> > bug, it does not mean that the original bug is also not there.
> > This will sure solve some subset of cases better then the current
> > logic. But I feel that that subset is smaller then what the current
> > logic solves.
>
> Counter-examples come up in basically every other bisection.
> For example:
>
> bisecting cause commit starting from ccda4af0f4b92f7b4c308d3acc262f4a7e3affad
> building syzkaller on 5f5f6d14e80b8bd6b42db961118e902387716bcb
> testing commit ccda4af0f4b92f7b4c308d3acc262f4a7e3affad with gcc (GCC) 8.1.0
> all runs: crashed: KASAN: null-ptr-deref Read in refcount_sub_and_test_checked
> testing release v4.19
> testing commit 84df9525b0c27f3ebc2ebb1864fa62a97fdedb7d with gcc (GCC) 8.1.0
> all runs: crashed: KASAN: null-ptr-deref Read in refcount_sub_and_test_checked
> testing release v4.18
> testing commit 94710cac0ef4ee177a63b5227664b38c95bbf703 with gcc (GCC) 8.1.0
> all runs: crashed: KASAN: null-ptr-deref Read in refcount_sub_and_test
> testing release v4.17
> testing commit 29dcea88779c856c7dc92040a0c01233263101d4 with gcc (GCC) 8.1.0
> all runs: crashed: KASAN: null-ptr-deref Read in refcount_sub_and_test


And to make things even more interesting, this later changes to "BUG:
unable to handle kernel NULL pointer dereference in vb2_vmalloc_put":

testing release v4.12
testing commit 6f7da290413ba713f0cdd9ff1a2a9bb129ef4f6c with gcc (GCC) 8.1.0
all runs: crashed: general protection fault in refcount_sub_and_test
testing release v4.11
testing commit a351e9b9fc24e982ec2f0e76379a49826036da12 with gcc (GCC) 7.3.0
all runs: crashed: BUG: unable to handle kernel NULL pointer
dereference in vb2_vmalloc_put

And since the original bug is in vb2 subsystem
(https://syzkaller.appspot.com/bug?id=17535f4bf5b322437f7c639b59161ce343fc55a9),
it's actually not clear even for me, if we should treat it as the same
bug or not. May be different manifestation of the same root cause, or
a different bug around.


> That's a different crash title, unless somebody explicitly code this case.
>
> Or, what crash is this?
>
> testing commit 52358cb5a310990ea5069f986bdab3620e01181f with gcc (GCC) 8.1.0
> run #1: crashed: general protection fault in cpuacct_charge
> run #2: crashed: WARNING: suspicious RCU usage in corrupted
> run #3: crashed: general protection fault in cpuacct_charge
> run #4: crashed: BUG: unable to handle kernel paging request in ipt_do_table
> run #5: crashed: KASAN: stack-out-of-bounds Read in cpuacct_charge
> run #6: crashed: WARNING: suspicious RCU usage
> run #7: crashed: no output from test machine
> run #8: crashed: no output from test machine
>
>
> Or, that "INFO: trying to register non-static key in can_notifier"
> does not do any testing, but is "WARNING in dma_buf_vunmap" still
> there or not?
>
> testing commit 6f7da290413ba713f0cdd9ff1a2a9bb129ef4f6c with gcc (GCC) 8.1.0
> all runs: crashed: WARNING in dma_buf_vunmap
> testing release v4.11
> testing commit a351e9b9fc24e982ec2f0e76379a49826036da12 with gcc (GCC) 7.3.0
> all runs: OK
> # git bisect start v4.12 v4.11
> Bisecting: 7831 revisions left to test after this (roughly 13 steps)
> [2bd80401743568ced7d303b008ae5298ce77e695] Merge tag 'gpio-v4.12-1' of
> git://git.kernel.org/pub/scm/linux/kernel/git/linusw/linux-gpio
> testing commit 2bd80401743568ced7d303b008ae5298ce77e695 with gcc (GCC) 7.3.0
> all runs: crashed: INFO: trying to register non-static key in can_notifier
> # git bisect bad 2bd80401743568ced7d303b008ae5298ce77e695
> Bisecting: 3853 revisions left to test after this (roughly 12 steps)
> [8d65b08debc7e62b2c6032d7fe7389d895b92cbc] Merge
> git://git.kernel.org/pub/scm/linux/kernel/git/davem/net-next
> testing commit 8d65b08debc7e62b2c6032d7fe7389d895b92cbc with gcc (GCC) 7.3.0
> all runs: crashed: INFO: trying to register non-static key in can_notifier
> # git bisect bad 8d65b08debc7e62b2c6032d7fe7389d895b92cbc
> Bisecting: 2022 revisions left to test after this (roughly 11 steps)
> [cec381919818a9a0cb85600b3c82404bdd38cf36] Merge tag
> 'mac80211-next-for-davem-2017-04-28' of
> git://git.kernel.org/pub/scm/linux/kernel/git/jberg/mac80211-next
> testing commit cec381919818a9a0cb85600b3c82404bdd38cf36 with gcc (GCC) 5.5.0
> all runs: crashed: INFO: trying to register non-static key in can_notifier
>
>
>
>
>
>
> > > syzbot has some knowledge about duplicates with different crash titles when people use "syz dup" command.
> >
> > This is very limited set of info. And in the end I think we've seen
> > all bug types being duped on all other bugs types pair-wise, and at
> > the same time we've seen all bug types being not dups to all other bug
> > types. So I don't see where this gets us.
> > And again as we go back in history all these titles change.
> >
> > > Also it might be worth to experiment with using neural networks to identify duplicates.
> > >
> > >
> > > target_crash = 'kernel panic: corrupted stack end in wb_workfn'
> > > test commit:
> > >         bad = false;
> > >         skip = true;
> > >         foreach run:
> > >                 run_started, crashed, crash := run_repro();
> > >
> > >                 //kernel built, booted, reproducer launched successfully
> > >                 if (run_started)
> > >                         skip = false;
> > >                 if (crashed && is_duplicates(crash, target_crash))
> > >                         bad = true;
> > >
> > >         if (skip)
> > >                 git bisect skip;
> > >         else if (bad)
> > >                 git bisect bad;
> > >         else
> > >                 git bisect good;