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From:   Linus Torvalds <torvalds@linux-foundation.org>
Date:   Thu, 24 Mar 2022 12:47:28 -0700
Message-ID: <CAHk-=wg++3S5Cvks-4xFCrD7qgZDibc5aMS4Bt=Pemm7FnOBZA@mail.gmail.com>
Subject: Re: [syzbot] general protection fault in list_lru_add
To:     syzbot <syzbot+f8c45ccc7d5d45fc5965@syzkaller.appspotmail.com>
Cc:     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>,
        Muchun Song <songmuchun@bytedance.com>,
        syzkaller-bugs <syzkaller-bugs@googlegroups.com>
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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.

             Linus