From: Miklos Szeredi <miklos@szeredi.hu>
To: Dmitry Vyukov <dvyukov@google.com>
Cc: syzbot <syzbot+d86c4426a01f60feddc7@syzkaller.appspotmail.com>,
bcrl <bcrl@kvack.org>, linux-aio <linux-aio@kvack.org>,
linux-fsdevel <linux-fsdevel@vger.kernel.org>,
LKML <linux-kernel@vger.kernel.org>,
syzkaller-bugs <syzkaller-bugs@googlegroups.com>,
Al Viro <viro@zeniv.linux.org.uk>
Subject: Re: possible deadlock in free_ioctx_users
Date: Mon, 10 Sep 2018 11:50:43 +0200 [thread overview]
Message-ID: <CAJfpegs72smmBfLdAwaOgQsLGsfdvWATv9BaNVvb0o4KdY3shA@mail.gmail.com> (raw)
In-Reply-To: <CACT4Y+bhGKrHk_BB4g9nDtRYD9VaaPyBTRxTo98r1BufAh6Z8A@mail.gmail.com>
On Mon, Sep 10, 2018 at 11:43 AM, Dmitry Vyukov <dvyukov@google.com> wrote:
> On Mon, Sep 10, 2018 at 11:28 AM, Miklos Szeredi <miklos@szeredi.hu> wrote:
>> On Sun, Sep 9, 2018 at 8:41 PM, syzbot
>> <syzbot+d86c4426a01f60feddc7@syzkaller.appspotmail.com> wrote:
>>> Hello,
>>>
>>> syzbot found the following crash on:
>>>
>>> HEAD commit: f8f65382c98a Merge tag 'for-linus' of git://git.kernel.org..
>>> git tree: upstream
>>> console output: https://syzkaller.appspot.com/x/log.txt?x=113260ae400000
>>> kernel config: https://syzkaller.appspot.com/x/.config?x=8f59875069d721b6
>>> dashboard link: https://syzkaller.appspot.com/bug?extid=d86c4426a01f60feddc7
>>> compiler: gcc (GCC) 8.0.1 20180413 (experimental)
>>> syz repro: https://syzkaller.appspot.com/x/repro.syz?x=120baa9e400000
>>> C reproducer: https://syzkaller.appspot.com/x/repro.c?x=13979cbe400000
>>>
>>> IMPORTANT: if you fix the bug, please add the following tag to the commit:
>>> Reported-by: syzbot+d86c4426a01f60feddc7@syzkaller.appspotmail.com
>>>
>>> random: sshd: uninitialized urandom read (32 bytes read)
>>> random: sshd: uninitialized urandom read (32 bytes read)
>>> random: sshd: uninitialized urandom read (32 bytes read)
>>>
>>> ========================================================
>>> WARNING: possible irq lock inversion dependency detected
>>> 4.19.0-rc2+ #229 Not tainted
>>> --------------------------------------------------------
>>> swapper/0/0 just changed the state of lock:
>>> 00000000c02bddef (&(&ctx->ctx_lock)->rlock){..-.}, at: spin_lock_irq
>>> include/linux/spinlock.h:354 [inline]
>>> 00000000c02bddef (&(&ctx->ctx_lock)->rlock){..-.}, at:
>>> free_ioctx_users+0xbc/0x710 fs/aio.c:603
>>> but this lock took another, SOFTIRQ-unsafe lock in the past:
>>> (&fiq->waitq){+.+.}
>>>
>>>
>>> and interrupts could create inverse lock ordering between them.
>>>
>>>
>>> other info that might help us debug this:
>>> Possible interrupt unsafe locking scenario:
>>>
>>> CPU0 CPU1
>>> ---- ----
>>> lock(&fiq->waitq);
>>> local_irq_disable();
>>> lock(&(&ctx->ctx_lock)->rlock);
>>> lock(&fiq->waitq);
>>> <Interrupt>
>>> lock(&(&ctx->ctx_lock)->rlock);
>>
>> Fuse device doesn't support AIO ops. So false positive, AFAICS.
>
> Hi Miklos,
>
> We still need to annotate this. How?
Good question.
Isn't lockdep assuming too much here? It hasn't shown that that
ctx_lock instance was actually called from interrupt context, has it?
Thanks,
Miklos
next prev parent reply other threads:[~2018-09-10 14:43 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-09-09 18:41 possible deadlock in free_ioctx_users syzbot
2018-09-09 19:11 ` Matthew Wilcox
2018-09-10 9:28 ` Miklos Szeredi
2018-09-10 9:43 ` Dmitry Vyukov
2018-09-10 9:50 ` Miklos Szeredi [this message]
2018-09-10 10:03 ` Dmitry Vyukov
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