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Mon, 02 Nov 2026 05:49:13 -0800 (PST) X-Received: by 2002:a5d:5e8c:0:b0:48e:679a:4b03 with SMTP id ffacd0b85a97d-48e6e4f8bbamr24526577f8f.45.1793627353329; Mon, 02 Nov 2026 05:49:13 -0800 (PST) Received: from jlelli-thinkpadt14gen4.remote.csb ([151.29.158.90]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-48e71b78a4csm19979575f8f.23.2026.11.02.05.49.12 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 02 Nov 2026 05:49:12 -0800 (PST) Date: Mon, 2 Nov 2026 14:49:10 +0100 From: Juri Lelli To: Tejun Heo Cc: Peter Zijlstra , Ingo Molnar , Vincent Guittot , Dietmar Eggemann , Steven Rostedt , Ben Segall , Mel Gorman , Valentin Schneider , K Prateek Nayak , linux-kernel@vger.kernel.org Subject: Re: [PATCH sched/urgent] sched/deadline: Fix stale rq->dl_server after a server pick returns RETRY_TASK Message-ID: References: <20261030221842.4071610-1-tj@kernel.org> X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: On 30/10/26 13:56, Tejun Heo wrote: > On Fri, Oct 30, 2026 at 12:18:42PM -1000, Tejun Heo wrote: > > __pick_task_dl() records the server in rq->dl_server whenever the server's > > pick returns non-NULL, RETRY_TASK included. __pick_next_task() clears > > rq->dl_server at its top, but a RETRY_TASK restarts the pick below that > > clear. put_prev_set_next_task() then hands the stale server to whatever the > > restarted pick takes. > > > > Since b3a2dfa8b42e ("sched/fair: Add newidle balance to pick_task_fair()"), > > fair_server_pick_task() returns RETRY_TASK when the newidle balance released > > the rq lock and a higher class task was enqueued meanwhile. > > > > That task, an RT task for example, then carries the fair server in > > p->dl_server until it is next put. The RV deadline monitors see the fair > > server switch in with it, and core scheduling, if enabled meanwhile, treats > > the task as deadline priority. > > > > Don't record the server when its pick returns RETRY_TASK. The restarted pick > > records whichever server it goes through, if any. > > > > Verified with a synthetic reproducer. > > > > Fixes: b3a2dfa8b42e ("sched/fair: Add newidle balance to pick_task_fair()") > > Signed-off-by: Tejun Heo > > Ugh, please ignore this one. Sent out the wrong patch. I'll test Juri's. uhu, don't think any of my recently shared patches deal with this case? :) Thanks, Juri