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From: Pavel Begunkov <[email protected]>
To: Jens Axboe <[email protected]>
Cc: [email protected], io-uring <[email protected]>
Subject: Re: [PATCH 5.10 1/5] io_uring: always let io_iopoll_complete() complete polled io.
Date: Tue, 8 Dec 2020 19:12:15 +0000	[thread overview]
Message-ID: <[email protected]> (raw)
In-Reply-To: <[email protected]>

On 07/12/2020 16:28, Jens Axboe wrote:
> On Sun, Dec 6, 2020 at 3:26 PM Pavel Begunkov <[email protected]> wrote:
>> From: Xiaoguang Wang <[email protected]>
>>
>> The reason is that once we got a non EAGAIN error in io_wq_submit_work(),
>> we'll complete req by calling io_req_complete(), which will hold completion_lock
>> to call io_commit_cqring(), but for polled io, io_iopoll_complete() won't
>> hold completion_lock to call io_commit_cqring(), then there maybe concurrent
>> access to ctx->defer_list, double free may happen.
>>
>> To fix this bug, we always let io_iopoll_complete() complete polled io.
> 
> This patch is causing hangs with iopoll testing, if you end up getting
> -EAGAIN on request submission. I've dropped it.

I fail to understand without debugging how does it happen, especially since
it shouldn't even get out of the while in io_wq_submit_work(). Is that
something obvious I've missed?

> 
> Reproducible with test/iopoll /dev/somedevice
> 
> where somedevice has a low queue depth and hits request starvation
> during the test.
> 

-- 
Pavel Begunkov

  reply	other threads:[~2020-12-08 20:37 UTC|newest]

Thread overview: 17+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-12-06 22:22 [PATCH 5.10 0/5] iopoll fixes Pavel Begunkov
2020-12-06 22:22 ` [PATCH 5.10 1/5] io_uring: always let io_iopoll_complete() complete polled io Pavel Begunkov
2020-12-07 16:28   ` Jens Axboe
2020-12-08 19:12     ` Pavel Begunkov [this message]
2020-12-08 19:17       ` Jens Axboe
2020-12-08 19:24         ` Pavel Begunkov
2020-12-08 21:10           ` Jens Axboe
2020-12-09 20:17             ` Pavel Begunkov
2020-12-10 17:38               ` Pavel Begunkov
2020-12-06 22:22 ` [PATCH 5.10 2/5] io_uring: fix racy IOPOLL completions Pavel Begunkov
2020-12-07 18:31   ` Pavel Begunkov
2020-12-06 22:22 ` [PATCH 5.10 3/5] io_uring: fix racy IOPOLL flush overflow Pavel Begunkov
2020-12-06 22:22 ` [PATCH 5.10 4/5] io_uring: fix io_cqring_events()'s noflush Pavel Begunkov
2020-12-06 22:22 ` [PATCH 5.10 5/5] io_uring: fix mis-seting personality's creds Pavel Begunkov
2020-12-07 15:05 ` [PATCH 5.10 0/5] iopoll fixes Jens Axboe
2020-12-07 15:24   ` Pavel Begunkov
2020-12-07 15:28     ` Jens Axboe

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