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Subject: Re: [PATCH 2/8] aio_poll_wake(): don't set ->woken if we ignore the
 wakeup
To:     Al Viro <viro@zeniv.linux.org.uk>,
        Linus Torvalds <torvalds@linux-foundation.org>
CC:     Eric Dumazet <eric.dumazet@gmail.com>,
        David Miller <davem@davemloft.net>,
        Jason Baron <jbaron@akamai.com>, <kgraul@linux.ibm.com>,
        <ktkhai@virtuozzo.com>, <kyeongdon.kim@lge.com>,
        Linux List Kernel Mailing <linux-kernel@vger.kernel.org>,
        Netdev <netdev@vger.kernel.org>, <pabeni@redhat.com>,
        <syzkaller-bugs@googlegroups.com>, <xiyou.wangcong@gmail.com>,
        Christoph Hellwig <hch@lst.de>, <bcrl@kvack.org>,
        <linux-fsdevel@vger.kernel.org>, <linux-aio@kvack.org>,
        <houtao1@huawei.com>, <yi.zhang@huawei.com>
References: <CAHk-=wghRmdYKRAwakeHmjcpbLt9fJAHyU2x8s_NZONhz6RTOw@mail.gmail.com>
 <20190307000316.31133-1-viro@ZenIV.linux.org.uk>
 <20190307000316.31133-2-viro@ZenIV.linux.org.uk>
 <20190307021844.GC2217@ZenIV.linux.org.uk>
From:   "zhengbin (A)" <zhengbin13@huawei.com>
Message-ID: <c02a5a3c-c617-b0d2-28a0-462f26b0c1c8@huawei.com>
Date:   Fri, 8 Mar 2019 19:16:28 +0800
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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@zeniv.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@huawei.com>
>> Signed-off-by: Al Viro <viro@zeniv.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 ;-/
> 
> .
>