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Mon, 09 Nov 2026 05:38:10 -0800 (PST) X-Received: by 2002:a05:6000:240f:b0:48d:f160:efad with SMTP id ffacd0b85a97d-49425566d13mr15141537f8f.30.1794231490148; Mon, 09 Nov 2026 05:38:10 -0800 (PST) Received: from jlelli-thinkpadt14gen4.remote.csb ([151.29.158.90]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-49597652ca7sm10965139f8f.39.2026.11.09.05.38.08 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 09 Nov 2026 05:38:09 -0800 (PST) Date: Mon, 9 Nov 2026 14:38:06 +0100 From: Juri Lelli To: Mathieu Desnoyers Cc: peterz@infradead.org, mingo@redhat.com, vincent.guittot@linaro.org, linux-kernel@vger.kernel.org, tglx@kernel.org, will@kernel.org, boqun@kernel.org, dietmar.eggemann@arm.com, rostedt@goodmis.org, bsegall@google.com, mgorman@suse.de, vschneid@redhat.com, kprateek.nayak@amd.com, luca.abeni@santannapisa.it, mathieu.poirier@linaro.org, longman@redhat.com, ridong.chen@linux.dev, tj@kernel.org, hannes@cmpxchg.org, mkoutny@suse.com, shuah@kernel.org, bigeasy@linutronix.de, clrkwllms@kernel.org, parri.andrea@gmail.com, m.szyprowski@samsung.com, kayracizmeci@gmail.com, weihengqiuu@gmail.com, cgroups@vger.kernel.org, linux-kselftest@vger.kernel.org, linux-rt-devel@lists.linux.dev, stable@vger.kernel.org Subject: Re: [PATCH v5 04/29] sched: Let a task boosted by a deadline waiter change its policy Message-ID: References: <20261108185406.1549770-1-mathieu.desnoyers@efficios.com> <20261108185406.1549770-5-mathieu.desnoyers@efficios.com> 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: <20261108185406.1549770-5-mathieu.desnoyers@efficios.com> Hello, On 08/11/26 13:53, Mathieu Desnoyers wrote: > A SCHED_OTHER or SCHED_FIFO task that holds an rt_mutex can be boosted > into the deadline class by a deadline waiter. Then a sched_setattr() or > sched_setscheduler() call on it fails with EBUSY, unless it asks for > SCHED_DEADLINE. sysrq-n would not reset it either. > > The admission test runs "if setscheduling to SCHED_DEADLINE (or > changing the parameters of a SCHED_DEADLINE task)", as its comment > says. sched_dl_overflow() then handles three cases, by the task's > policy: the task enters, leaves or stays in SCHED_DEADLINE. But the > call site tests dl_task(p). That tests the priority, so a boosted task > passes it. For such a task and another policy, sched_dl_overflow() > matches no case and returns -1. > > Fix this by testing the policy, with task_has_dl_policy(). A boosted > task has no bandwidth of its own to admit or release. > > Now sysrq-n can take a boosted task out of the class. > normalize_rt_tasks() calls __sched_setscheduler() without pi, so the > task gets its normal priority. Nothing then drops the boost. At the > unlock, rt_mutex_setprio() sees no change of priority. The pi_se of the > task would keep pointing to the waiter, which can exit. So also drop the > boost in __setscheduler_dl_pi() when the task leaves the class, as > rt_mutex_setprio() does. > > The boosted_owner_policy case of deadline_bw_test, added later in this > series, fails with EBUSY on v7.4-rc1. It passes with this series. The > sysrq_boosted_owner case of deadline_switch_test tests the sysrq-n path. > > Fixes: 332ac17ef5bf ("sched/deadline: Add bandwidth management for SCHED_DEADLINE tasks") > Cc: stable@vger.kernel.org > Signed-off-by: Mathieu Desnoyers > --- Reviewed-by: Juri Lelli Thanks, Juri