From: Pavel Begunkov <asml.silence@gmail.com>
To: Jens Axboe <axboe@kernel.dk>
Cc: xiaoguang.wang@linux.alibaba.com, io-uring <io-uring@vger.kernel.org>
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: <d9f677a4-1ac0-0e64-5c2a-497cac9dc8e5@gmail.com> (raw)
In-Reply-To: <10e20bd3-b08f-98b8-f857-8b9a75a511dd@kernel.dk>
On 07/12/2020 16:28, Jens Axboe wrote:
> On Sun, Dec 6, 2020 at 3:26 PM Pavel Begunkov <asml.silence@gmail.com> wrote:
>> From: Xiaoguang Wang <xiaoguang.wang@linux.alibaba.com>
>>
>> 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
next prev parent 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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