linux-kernel - Re: [PATCH 2/8] aio_poll_wake(): don't set ->woken if we ignore the wakeup

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Date:   Fri, 8 Mar 2019 19:16:28 +0800
From:   "zhengbin (A)" <zhengbin13@...wei.com>
To:     Al Viro <viro@...iv.linux.org.uk>,
        Linus Torvalds <torvalds@...ux-foundation.org>
CC:     Eric Dumazet <eric.dumazet@...il.com>,
        David Miller <davem@...emloft.net>,
        Jason Baron <jbaron@...mai.com>, <kgraul@...ux.ibm.com>,
        <ktkhai@...tuozzo.com>, <kyeongdon.kim@....com>,
        Linux List Kernel Mailing <linux-kernel@...r.kernel.org>,
        Netdev <netdev@...r.kernel.org>, <pabeni@...hat.com>,
        <syzkaller-bugs@...glegroups.com>, <xiyou.wangcong@...il.com>,
        Christoph Hellwig <hch@....de>, <bcrl@...ck.org>,
        <linux-fsdevel@...r.kernel.org>, <linux-aio@...ck.org>,
        <houtao1@...wei.com>, <yi.zhang@...wei.com>
Subject: Re: [PATCH 2/8] aio_poll_wake(): don't set ->woken if we ignore the
 wakeup

So, what should we do?

On 2019/3/7 10:18, Al Viro wrote:
> On Thu, Mar 07, 2019 at 12:03:10AM +0000, Al Viro wrote:
>> From: Al Viro <viro@...iv.linux.org.uk>
>>
>> In case of early wakeups, aio_poll() assumes that aio_poll_complete()
>> has either already happened or is imminent.  In that case we do not
>> want to put iocb on the list of cancellables.  However, ignored
>> wakeups need to be treated as if wakeup has not happened at all.
>> Trivially fixed by having aio_poll_wake() set ->woken only after
>> it's committed to taking iocb out of the waitqueue.
>>
>> Spotted-by: zhengbin <zhengbin13@...wei.com>
>> Signed-off-by: Al Viro <viro@...iv.linux.org.uk>
> 
> ... and unfortunately it's worse than just that - what both of us
> have missed is that one could have non-specific wakep + schedule_work +
> aio_poll_complete_work() rechecking ->poll(), seeing nothing of
> interest and reinserting into queue.  All before vfs_poll() manages
> to return into aio_poll().  The window is harder to hit, but it's
> still there, with exact same "failed to add to cancel list" kind of bug
> if we do hit it ;-/
> 
> .
>