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Tue, 22 Sep 2026 05:41:20 -0700 (PDT) Received: from jlelli-thinkpadt14gen4.remote.csb ([176.206.14.6]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-49fdaa99b8bsm36594555e9.1.2026.09.22.05.41.19 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 22 Sep 2026 05:41:19 -0700 (PDT) Date: Tue, 22 Sep 2026 14:41:17 +0200 From: Juri Lelli To: Donggeun Yoo Cc: mingo@redhat.com, peterz@infradead.org, vincent.guittot@linaro.org, dietmar.eggemann@arm.com, rostedt@goodmis.org, bsegall@google.com, mgorman@suse.de, vschneid@redhat.com, kprateek.nayak@amd.com, longman@redhat.com, tj@kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH] sched: Restore the normalize_rt_tasks() cpuset_mutex exemption Message-ID: References: <20260922030738.1613919-1-donggeunyoo.kernel@gmail.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20260922030738.1613919-1-donggeunyoo.kernel@gmail.com> Hello, On 22/09/26 12:07, Donggeun Yoo wrote: > sysrq-n runs normalize_rt_tasks(), which walks the task list under > read_lock(&tasklist_lock) and hands every user RT or deadline task to > __sched_setscheduler() with pi == false. __sched_setscheduler() takes > cpuset_mutex whenever the old or the new policy is deadline, and > cpuset_lock() is a plain mutex_lock(), so a single SCHED_DEADLINE user > task makes the sysrq handler sleep in atomic context: > > sysrq: Nice All RT Tasks > BUG: sleeping function called from invalid context at kernel/locking/mutex.c:623 > in_atomic(): 1, irqs_disabled(): 0, non_block: 0, pid: 1, name: init > preempt_count: 1, expected: 0 > RCU nest depth: 1, expected: 0 > locks held by init/1: 3, last CPU#1: > #0: ffff9fa2c34e1470 (sb_writers#3){.+.+}-{0:0}, at: ksys_write+0x74/0xf0 > #1: ffffffffb8f66540 (rcu_read_lock){....}-{1:3}, at: __handle_sysrq+0x3a/0x110 > #2: ffffffffb8e060d8 (tasklist_lock){.+.+}-{3:3}, at: normalize_rt_tasks+0x34/0x150 > Call Trace: > __might_resched.cold+0xe3/0xf5 > __mutex_lock+0x8a/0x11c0 > __sched_setscheduler+0x35f/0x9c0 > normalize_rt_tasks+0xe6/0x150 > __handle_sysrq.cold+0x9b/0xde > write_sysrq_trigger+0x65/0x90 > > Test pi along with the policy. The only pi == false caller is > normalize_rt_tasks(), where the lock is given up since the sysrq > emergency already voids deadline guarantees. > > Fixes: 111cd11bbc54 ("sched/cpuset: Bring back cpuset_mutex") > Signed-off-by: Donggeun Yoo > Cc: stable@vger.kernel.org > --- Ah, yes indeed. Acked-by: Juri Lelli Thanks! Juri