From: Pavel Begunkov <[email protected]>
To: Xiaoguang Wang <[email protected]>,
[email protected]
Cc: [email protected], [email protected]
Subject: Re: [PATCH] io_uring: hold uring_lock to complete faild polled io in io_wq_submit_work()
Date: Sun, 20 Dec 2020 19:36:06 +0000 [thread overview]
Message-ID: <[email protected]> (raw)
In-Reply-To: <[email protected]>
On 20/12/2020 19:34, Pavel Begunkov wrote:
> On 14/12/2020 15:49, Xiaoguang Wang wrote:
>> io_iopoll_complete() does not hold completion_lock to complete polled
>> io, so in io_wq_submit_work(), we can not call io_req_complete() directly,
>> to complete polled io, otherwise there maybe concurrent access to cqring,
>> defer_list, etc, which is not safe. Commit dad1b1242fd5 ("io_uring: always
>> let io_iopoll_complete() complete polled io") has fixed this issue, but
>> Pavel reported that IOPOLL apart from rw can do buf reg/unreg requests(
>> IORING_OP_PROVIDE_BUFFERS or IORING_OP_REMOVE_BUFFERS), so the fix is
>> not good.
>>
>> Given that io_iopoll_complete() is always called under uring_lock, so here
>> for polled io, we can also get uring_lock to fix this issue.
>
> This returns it to the state it was before fixing + mutex locking for
> IOPOLL, and it's much better than having it half-broken as it is now.
btw, comments are over 80, but that's minor.
>
> Cc: <[email protected]> # 5.5+
> Reviewed-by: Pavel Begunkov <[email protected]>
>
>>
>> Fixes: dad1b1242fd5 ("io_uring: always let io_iopoll_complete() complete polled io")
>> Signed-off-by: Xiaoguang Wang <[email protected]>
>> ---
>> fs/io_uring.c | 25 +++++++++++++++----------
>> 1 file changed, 15 insertions(+), 10 deletions(-)
>>
>> diff --git a/fs/io_uring.c b/fs/io_uring.c
>> index f53356ced5ab..eab3d2b7d232 100644
>> --- a/fs/io_uring.c
>> +++ b/fs/io_uring.c
>> @@ -6354,19 +6354,24 @@ static struct io_wq_work *io_wq_submit_work(struct io_wq_work *work)
>> }
>>
>> if (ret) {
>> + bool iopoll_enabled = req->ctx->flags & IORING_SETUP_IOPOLL;
>> +
>> /*
>> - * io_iopoll_complete() does not hold completion_lock to complete
>> - * polled io, so here for polled io, just mark it done and still let
>> - * io_iopoll_complete() complete it.
>> + * io_iopoll_complete() does not hold completion_lock to complete polled
>> + * io, so here for polled io, we can not call io_req_complete() directly,
>> + * otherwise there maybe concurrent access to cqring, defer_list, etc,
>> + * which is not safe. Given that io_iopoll_complete() is always called
>> + * under uring_lock, so here for polled io, we also get uring_lock to
>> + * complete it.
>> */
>> - if (req->ctx->flags & IORING_SETUP_IOPOLL) {
>> - struct kiocb *kiocb = &req->rw.kiocb;
>> + if (iopoll_enabled)
>> + mutex_lock(&req->ctx->uring_lock);
>>
>> - kiocb_done(kiocb, ret, NULL);
>> - } else {
>> - req_set_fail_links(req);
>> - io_req_complete(req, ret);
>> - }
>> + req_set_fail_links(req);
>> + io_req_complete(req, ret);
>> +
>> + if (iopoll_enabled)
>> + mutex_unlock(&req->ctx->uring_lock);
>> }
>>
>> return io_steal_work(req);
>>
>
--
Pavel Begunkov
next prev parent reply other threads:[~2020-12-21 4:50 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-12-14 15:49 [PATCH] io_uring: hold uring_lock to complete faild polled io in io_wq_submit_work() Xiaoguang Wang
2020-12-14 17:48 ` Pavel Begunkov
2020-12-15 2:28 ` Xiaoguang Wang
2020-12-15 11:08 ` Pavel Begunkov
2020-12-20 19:34 ` Pavel Begunkov
2020-12-20 19:36 ` Pavel Begunkov [this message]
2020-12-22 23:41 ` Jens Axboe
2020-12-23 2:12 ` Xiaoguang Wang
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