From: Jens Axboe <[email protected]>
To: Xiaoguang Wang <[email protected]>,
[email protected]
Cc: [email protected]
Subject: Re: [PATCH v2] io_uring: fix possible poll event lost in multi shot mode
Date: Fri, 3 Sep 2021 09:01:47 -0600 [thread overview]
Message-ID: <[email protected]> (raw)
In-Reply-To: <[email protected]>
On 9/3/21 8:24 AM, Xiaoguang Wang wrote:
> IIUC, IORING_POLL_ADD_MULTI is similar to epoll's edge-triggered mode,
> that means once one pure poll request returns one event(cqe), we'll
> need to read or write continually until EAGAIN is returned, then I think
> there is a possible poll event lost race in multi shot mode:
>
> t1 poll request add | |
> t2 | |
> t3 event happens | |
> t4 task work add | |
> t5 | task work run |
> t6 | commit one cqe |
> t7 | | user app handles cqe
> t8 | new event happen |
> t9 | add back to waitqueue |
> t10 |
>
> After t6 but before t9, if new event happens, there'll be no wakeup
> operation, and if user app has picked up this cqe in t7, read or write
> until EAGAIN is returned. In t8, new event happens and will be lost,
> though this race window maybe small.
>
> To fix this possible race, add poll request back to waitqueue before
> committing cqe.
Applied, thanks.
--
Jens Axboe
prev parent reply other threads:[~2021-09-03 15:01 UTC|newest]
Thread overview: 2+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-09-03 14:24 [PATCH v2] io_uring: fix possible poll event lost in multi shot mode Xiaoguang Wang
2021-09-03 15:01 ` Jens Axboe [this message]
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