From: Miklos Szeredi <miklos@szeredi.hu>
To: Christoph Hellwig <hch@infradead.org>
Cc: syzbot <syzbot+5b1df0420c523b45a953@syzkaller.appspotmail.com>,
bcrl <bcrl@kvack.org>, linux-aio <linux-aio@kvack.org>,
linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org,
syzkaller-bugs <syzkaller-bugs@googlegroups.com>,
Al Viro <viro@zeniv.linux.org.uk>,
Andrea Arcangeli <aarcange@redhat.com>,
Andrew Morton <akpm@linux-foundation.org>
Subject: Re: possible deadlock in aio_poll
Date: Mon, 10 Sep 2018 20:14:20 +0200 [thread overview]
Message-ID: <CAJfpeguWqJgU8EfjvOtsBYRbbY2J7Ck2oNUcLNS8my9g2eNZfA@mail.gmail.com> (raw)
In-Reply-To: <20180910165317.GA3237@infradead.org>
On Mon, Sep 10, 2018 at 6:53 PM, Christoph Hellwig <hch@infradead.org> wrote:
> On Mon, Sep 10, 2018 at 12:41:05AM -0700, syzbot wrote:
>> =====================================================
>> WARNING: SOFTIRQ-safe -> SOFTIRQ-unsafe lock order detected
>> 4.19.0-rc2+ #229 Not tainted
>> -----------------------------------------------------
>> syz-executor2/9399 [HC0[0]:SC0[0]:HE0:SE1] is trying to acquire:
>> 00000000126506e0 (&ctx->fd_wqh){+.+.}, at: spin_lock
>> include/linux/spinlock.h:329 [inline]
>> 00000000126506e0 (&ctx->fd_wqh){+.+.}, at: aio_poll+0x760/0x1420
>> fs/aio.c:1747
>>
>> and this task is already holding:
>> 000000002bed6bf6 (&(&ctx->ctx_lock)->rlock){..-.}, at: spin_lock_irq
>> include/linux/spinlock.h:354 [inline]
>> 000000002bed6bf6 (&(&ctx->ctx_lock)->rlock){..-.}, at: aio_poll+0x738/0x1420
>> fs/aio.c:1746
>> which would create a new lock dependency:
>> (&(&ctx->ctx_lock)->rlock){..-.} -> (&ctx->fd_wqh){+.+.}
>
> ctx->fd_wqh seems to only exist in userfaultfd, which indeed seems
> to do strange open coded waitqueue locking, and seems to fail to disable
> irqs. Something like this should fix it:
Why do pollable waitqueues need to disable interrupts generally?
I don't see anything fundamental in the poll interface to force this
requirement on users of that interface.
Thanks,
Miklos
next prev parent reply other threads:[~2018-09-10 23:09 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-09-10 7:41 possible deadlock in aio_poll syzbot
2018-09-10 16:53 ` Christoph Hellwig
2018-09-10 18:14 ` Miklos Szeredi [this message]
2018-09-11 6:33 ` Christoph Hellwig
2018-09-11 7:20 ` Miklos Szeredi
2018-10-17 23:55 ` Andrea Arcangeli
2018-10-27 6:16 ` syzbot
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