From mboxrd@z Thu Jan 1 00:00:00 1970 Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.remote-ip=158.69.130.18 ARC-Seal: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; cv=none; t=1794164059; b=be4OybaX0UWl5XejJz45xIDGrbVO4LJVLNikFAR+9LjFgErO17bo/DmJ+BhYa/hm8Go+ OdQSxjEM03ssP+Mq4C87vYJHcsKs8u3zRIRr3FEaSq/Ca6zKqWqMsN/DDaVkJAl4xqsFG IDLb2EJa3tTTkzoOToqsRrbQETA+HvzxdSNVn0TvNXOKNPTBM5klaRUePlNLexwMA+Quv Xc5iiyrZtgS2R/LgzhO6rjlSc+x3hXwY5C4Y96sOyHL3T8HgajvvwES2TCWcbUzgScBLm wVsokgl6KlKY/6LMQcZBHpvRrYg2stS6RGay8idONiBcEMHCjssBDCP4p370w6KWxjA== ARC-Message-Signature: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; c=relaxed/relaxed; t=1794164059; h=DMARC-Filter:DKIM-Signature:Received:From:To:Cc:Subject:Date: Message-Id:X-Mailer:In-Reply-To:References:MIME-Version: Content-Transfer-Encoding; bh=QrZa6e0JD0lct8uAlK8UrXwI3QzrNKc9JZDyt1pikXM=; b=2xVOE+9hMyCFeIg1umYqdENPMtLSectAgciurVPC3svIqcpTfrwUOoH8ekTwM0scWA4X nRQvQcibQQxEwwEhRQmFUj7Vlxnh98bk2l1yDt8Md1MAJtdY1dOLwOobqTt8fcQ2L4LDf LWqbVH8QXup6eEOhnpWYKr8zn/4nh8HGfpA0SXvN9bT4w9W9DLfU1QHEtrRky1zo7Dz3l FdVwI3SEws2GhH56ZDDSj2hLx29o0PMrE8o0WAzQ2VJUR0olU9N2rPuC5Ma/W8t4x8wWk /OSXKm98VzT+VVhbTPR3twfKkBywmL8wxxqOBajpPLVbqGQrkLOjaEhl19geB884mfw== ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dmarc=pass header.from=efficios.com; spf=pass smtp.mailfrom=efficios.com; dkim=pass header.d=efficios.com header.i=@efficios.com header.a=rsa-sha256 header.s=smtpout1 header.b=eQdWvPWn; arc=none smtp.remote-ip=158.69.130.18 Received: from smtpout.efficios.com (smtpout.efficios.com [158.69.130.18]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature ECDSA (prime256v1)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id F157B606D80A; Sun, 8 Nov 2026 18:54:18 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.4.2 smtp.subspace.kernel.org F157B606D80A Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=efficios.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=efficios.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=efficios.com header.i=@efficios.com header.a=rsa-sha256 header.s=smtpout1 header.b=eQdWvPWn DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=efficios.com; s=smtpout1; t=1794164058; bh=QrZa6e0JD0lct8uAlK8UrXwI3QzrNKc9JZDyt1pikXM=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=eQdWvPWnTw89FMWn2HQvPemvosCK3HlARLCbMfrO7mEVFu/UBKr6vNn6Lv6NbrkHq j/F23xEnHYGckUhbxy3xtLP7P7yLmcMWe7gXB+vQn5pp+ItHkMombdrSBnzS0mSR4o 4SsbBRgrxKeCCLb8ohjoIpMuG592OvmLe3bocskOy9jS4y9jS0BMgbN1p5HnaaMP0y 0jQRu0tRfVLMcER+ZHG4YFto0gsnDQJCNV9XrhARc6fAKWnw8quDRmJS4rVv/pAp6k 6LTpBw9DhUHcZFYaO/fLyhwljr/oFVbui4aOz8CwV9rGgX7L7QVeND5L2YOwADUKg5 xlGAKedkLwnnw== Received: from thinkos.internal.efficios.com (unknown [64.58.40.251]) by smtpout.efficios.com (Postfix) with ESMTPSA id 4jN2Bx6TqSzMkD; Sun, 08 Nov 2026 13:54:17 -0500 (EST) From: Mathieu Desnoyers To: juri.lelli@redhat.com, peterz@infradead.org, mingo@redhat.com, vincent.guittot@linaro.org Cc: linux-kernel@vger.kernel.org, Mathieu Desnoyers , 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: [PATCH v5 04/29] sched: Let a task boosted by a deadline waiter change its policy Date: Sun, 8 Nov 2026 13:53:41 -0500 Message-Id: <20261108185406.1549770-5-mathieu.desnoyers@efficios.com> X-Mailer: git-send-email 2.39.5 In-Reply-To: <20261108185406.1549770-1-mathieu.desnoyers@efficios.com> References: <20261108185406.1549770-1-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-Transfer-Encoding: 8bit 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 --- kernel/sched/syscalls.c | 14 +++++++++++++- 1 file changed, 13 insertions(+), 1 deletion(-) diff --git a/kernel/sched/syscalls.c b/kernel/sched/syscalls.c index 894f93a80d5d..56ce2352e89e 100644 --- a/kernel/sched/syscalls.c +++ b/kernel/sched/syscalls.c @@ -304,6 +304,13 @@ static inline void __setscheduler_dl_pi(int newprio, int policy, scope->flags |= ENQUEUE_REPLENISH; } } + + /* + * Without pi, as from normalize_rt_tasks(), a boosted task can leave + * the class. Drop its boost then, as rt_mutex_setprio() does. + */ + if (!dl_prio(newprio)) + p->dl.pi_se = &p->dl; } #else /* !CONFIG_RT_MUTEXES */ static inline void __setscheduler_dl_pi(int newprio, int policy, @@ -691,12 +698,17 @@ int __sched_setscheduler(struct task_struct *p, * is available. Keep this check last. If a later check failed, * nothing would give back the bandwidth it reserves. * + * Test the policy, not the priority. A task boosted into the class + * by priority inheritance has no bandwidth of its own to admit or + * release. + * * With SCHED_FLAG_KEEP_PARAMS, the task keeps its parameters, so * there is nothing to admit. The parameters in attr may also be * stale: sys_sched_setattr() read them from the task without a lock. */ if (!(attr->sched_flags & SCHED_FLAG_KEEP_PARAMS) && - (dl_policy(policy) || dl_task(p)) && sched_dl_overflow(p, policy, attr)) { + (dl_policy(policy) || task_has_dl_policy(p)) && + sched_dl_overflow(p, policy, attr)) { retval = -EBUSY; goto unlock; } -- 2.47.3