linux-kernel - Re: possible deadlock in aio

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Message-ID: <CAJfpegtS8QMfhNMFV3i6GycqmXsLNYXvKjRm3wG79PFuF1VvuA@mail.gmail.com>
Date:   Tue, 11 Sep 2018 09:20:40 +0200
From:   Miklos Szeredi <miklos@...redi.hu>
To:     Christoph Hellwig <hch@...radead.org>
Cc:     syzbot <syzbot+5b1df0420c523b45a953@...kaller.appspotmail.com>,
        bcrl <bcrl@...ck.org>, linux-aio <linux-aio@...ck.org>,
        linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
        syzkaller-bugs <syzkaller-bugs@...glegroups.com>,
        Al Viro <viro@...iv.linux.org.uk>,
        Andrea Arcangeli <aarcange@...hat.com>,
        Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: possible deadlock in aio_poll

On Tue, Sep 11, 2018 at 8:33 AM, Christoph Hellwig <hch@...radead.org> wrote:
> On Mon, Sep 10, 2018 at 08:14:20PM +0200, Miklos Szeredi wrote:
>> Why do pollable waitqueues need to disable interrupts generally?
>
> Any waitqueue needs to disable interrupts for consistency.  We
> always use spin_lock_irqsave in __wake_up_common_lock() for example.

There are the _locked (non _irq) variants that do not.

And poll/select/etc don't impose non-interuptibility on wakeups
either.  So it looks like it's just aio that has weird spin lock
dependencies that forces this requirement on a waitq used in ->poll().

Thanks,
Miklos