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From:   Muchun Song <songmuchun@bytedance.com>
Date:   Fri, 25 Mar 2022 09:43:51 +0800
Message-ID: <CAMZfGtVHSWAzLN+FzOL0MyedcXc5UAaGuc4OufUwkLzWe2KWvQ@mail.gmail.com>
Subject: Re: [syzbot] general protection fault in list_lru_add
To:     Linus Torvalds <torvalds@linux-foundation.org>
Cc:     syzbot <syzbot+f8c45ccc7d5d45fc5965@syzkaller.appspotmail.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        Dmitry Vyukov <dvyukov@google.com>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        Linux-MM <linux-mm@kvack.org>,
        syzkaller-bugs <syzkaller-bugs@googlegroups.com>
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On Fri, Mar 25, 2022 at 3:47 AM Linus Torvalds
<torvalds@linux-foundation.org> wrote:
>
> On Thu, Mar 24, 2022 at 12:45 PM Linus Torvalds
> <torvalds@linux-foundation.org> wrote:
> >
> > On Thu, Mar 24, 2022 at 12:41 PM syzbot
> > <syzbot+f8c45ccc7d5d45fc5965@syzkaller.appspotmail.com> wrote:
> > >
> > > syzbot has tested the proposed patch and the reproducer did not trigger any issue:
> >
> > Heh, well that's unfortunate.
> >
> > I think the issue is that it triggered a new BUG() that didn't match
> > the previous NULL pointer dereference, so it thinks things are
> > "fixed".
>
> Oh, no, it's because it used the truncated patch that didn't do anything:
>
> > patch:          https://syzkaller.appspot.com/x/patch.diff?x=1208043d700000
>
> and maybe (due to the racy nature) nothing actually happened.
>

It is not easy to reproduce. I'm also trying to reproduce locally.

#syz test: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git
5abc1e37afa0335c52608d640fd30910b2eeda21

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