linux-kernel - Re: [syzbot] general protection fault in list_lru

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Date:   Thu, 24 Mar 2022 16:44:18 +0800
From:   Muchun Song <songmuchun@...edance.com>
To:     Linus Torvalds <torvalds@...ux-foundation.org>
Cc:     syzbot <syzbot+f8c45ccc7d5d45fc5965@...kaller.appspotmail.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Linux-MM <linux-mm@...ck.org>,
        syzkaller-bugs <syzkaller-bugs@...glegroups.com>
Subject: Re: [syzbot] general protection fault in list_lru_add

On Thu, Mar 24, 2022 at 11:05 AM Linus Torvalds
<torvalds@...ux-foundation.org> wrote:
>
> On Wed, Mar 23, 2022 at 7:19 PM Muchun Song <songmuchun@...edance.com> wrote:
> >
> > After this commit, the rules of dentry allocations changed.
> > The dentry should be allocated by kmem_cache_alloc_lru()
>
> Yeah, I looked at that, but I can't find any way there could be other
> allocations - not only are there strict rules how to initialize
> everything, but the dentries are free'd using
>
>         kmem_cache_free(dentry_cache, dentry);
>
> and as a result if they were allocated any other way I would expect
> things would go south very quickly.
>
> The only other thing I could come up with is some breakage in the
> superblock lifetime so that &dentry->d_sb->s_dentry_lru would have
> problems, but again, this is *such* core code and not some unusual
> path, that I would be very very surprised if it wouldn't have
> triggered other issues long long ago.
>
> That's why I'd be more inclined to worry about the list_lru code being
> somehow broken.
>

I also have the same concern.  I have been trying for a few hours to
reproduce this issue, but it didn't oops on my test machine.  And I'll
continue reproducing this.

Thanks.