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charset="ISO-8859-1" Content-Transfer-Encoding: quoted-printable User-Agent: Evolution 3.52.4 Precedence: bulk X-Mailing-List: io-uring@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-AntiAbuse: This header was added to track abuse, please include it with any abuse report X-AntiAbuse: Primary Hostname - cloud48395.mywhc.ca X-AntiAbuse: Original Domain - vger.kernel.org X-AntiAbuse: Originator/Caller UID/GID - [47 12] / [47 12] X-AntiAbuse: Sender Address Domain - trillion01.com X-Get-Message-Sender-Via: cloud48395.mywhc.ca: authenticated_id: olivier@trillion01.com X-Authenticated-Sender: cloud48395.mywhc.ca: olivier@trillion01.com X-Source: X-Source-Args: X-Source-Dir: On Mon, 2024-08-12 at 14:40 -0600, Jens Axboe wrote: >=20 > @@ -174,9 +174,8 @@ static void io_napi_blocking_busy_loop(struct > io_ring_ctx *ctx, > =A0 do { > =A0 is_stale =3D __io_napi_do_busy_loop(ctx, > loop_end_arg); > =A0 } while (!io_napi_busy_loop_should_end(iowq, start_time) && > !loop_end_arg); > - rcu_read_unlock(); > - > =A0 io_napi_remove_stale(ctx, is_stale); > + rcu_read_unlock(); > =A0} >=20 > @@ -309,9 +309,8 @@ int io_napi_sqpoll_busy_poll(struct io_ring_ctx > *ctx) > =A0 > =A0 rcu_read_lock(); > =A0 is_stale =3D __io_napi_do_busy_loop(ctx, NULL); > - rcu_read_unlock(); > - > =A0 io_napi_remove_stale(ctx, is_stale); > + rcu_read_unlock(); > =A0 return 1; > =A0} > =A0 >=20 Jens, I have big doubts that moving the rcu_read_unlock() call is correct. The read-only list access if performed by the busy loops block. io_napi_remove_stale() is then modifying the list after having acquired the spinlock. IMHO, you should not hold the RCU read lock when you are updating the data. I even wonder is this could not be a possible livelock cause...