From: Stefan Roesch <shr@devkernel.io>
To: Jens Axboe <axboe@kernel.dk>
Cc: io-uring@vger.kernel.org, kernel-team@fb.com,
ammarfaizi2@gnuweeb.org,
Olivier Langlois <olivier@trillion01.com>,
Jakub Kicinski <kuba@kernel.org>
Subject: Re: [PATCH v12 2/5] io-uring: add napi busy poll support
Date: Thu, 04 May 2023 09:06:10 -0700 [thread overview]
Message-ID: <qvqwa5ykcc8b.fsf@devbig1114.prn1.facebook.com> (raw)
In-Reply-To: <acd78dcf-f145-d7d3-a30d-4b6694089023@kernel.dk>
Jens Axboe <axboe@kernel.dk> writes:
>
> I mentioned this in our out-of-band discussions on this patch set, and
> we cannot call napi_busy_loop() under rcu_read_lock() if loop_end and
> loop_end_arg is set AND loop_end() doesn't always return true. Because
> otherwise we can end up with napi_busy_loop() doing:
>
> if (unlikely(need_resched())) {
> if (napi_poll)
> busy_poll_stop(napi, have_poll_lock, prefer_busy_poll, budget);
> preempt_enable();
> rcu_read_unlock();
> cond_resched();
> if (loop_end(loop_end_arg, start_time))
> return;
> goto restart;
> }
>
> and hence we're now scheduling with rcu read locking disabled. So we
> need to handle that case appropriately as well.
I'll have a look.
next prev parent reply other threads:[~2023-05-04 16:06 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-05-02 16:53 [PATCH v12 0/5] io_uring: add napi busy polling support Stefan Roesch
2023-05-02 16:53 ` [PATCH v12 1/5] io-uring: move io_wait_queue definition to header file Stefan Roesch
2023-05-02 16:53 ` [PATCH v12 2/5] io-uring: add napi busy poll support Stefan Roesch
2023-05-03 17:40 ` Jens Axboe
2023-05-04 16:06 ` Stefan Roesch [this message]
2023-05-02 16:53 ` [PATCH v12 3/5] io-uring: add sqpoll support for napi busy poll Stefan Roesch
2023-05-02 16:53 ` [PATCH v12 4/5] io_uring: add register/unregister napi function Stefan Roesch
2023-05-02 16:53 ` [PATCH v12 5/5] io_uring: add prefer busy poll to register and unregister napi api Stefan Roesch
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