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Subject: Re: [syzbot] INFO: task hung in io_sq_thread_park (2)
To:     Pavel Begunkov <asml.silence@gmail.com>,
        syzbot <syzbot+ac957324022b7132accf@syzkaller.appspotmail.com>,
        io-uring@vger.kernel.org, linux-kernel@vger.kernel.org,
        mingo@kernel.org, mingo@redhat.com, peterz@infradead.org,
        rostedt@goodmis.org, syzkaller-bugs@googlegroups.com,
        will@kernel.org
References: <000000000000e1f38205c73b72cc@google.com>
 <c57f80f7-440b-9f12-a7b7-a58ed7ab400a@gmail.com>
From:   Jens Axboe <axboe@kernel.dk>
Message-ID: <3ff29943-0f93-1381-1c8a-46f80aecd0b4@kernel.dk>
Date:   Mon, 19 Jul 2021 11:13:52 -0600
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On 7/19/21 10:57 AM, Pavel Begunkov wrote:
> On 7/16/21 11:57 AM, syzbot wrote:
>> Hello,
>>
>> syzbot has tested the proposed patch but the reproducer is still triggering an issue:
>> WARNING in io_uring_cancel_generic
> 
> __arm_poll doesn't remove a second poll entry in case of failed
> __io_queue_proc(), it's most likely the cause here.
> 
> #syz test: https://github.com/isilence/linux.git syztest_sqpoll_hang

Was my thought on seeing the last debug run too. Haven't written a test
case, but my initial thought was catching this at the time that double
poll is armed, in __io_queue_proc(). Totally untested, just tossing
it out there.


diff --git a/fs/io_uring.c b/fs/io_uring.c
index 0cac361bf6b8..ed33de5fffd2 100644
--- a/fs/io_uring.c
+++ b/fs/io_uring.c
@@ -5002,6 +5002,9 @@ static void __io_queue_proc(struct io_poll_iocb *poll, struct io_poll_table *pt,
 	if (unlikely(poll->head)) {
 		struct io_poll_iocb *poll_one = poll;
 
+		/* first poll failed, don't arm double poll */
+		if (pt->error)
+			return;
 		/* already have a 2nd entry, fail a third attempt */
 		if (*poll_ptr) {
 			pt->error = -EINVAL;

-- 
Jens Axboe