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=1794015907; b=DqLjMMkfWaZwRwSuY8NIrCjh5SQks17LeP2JF76IYCJuO7502RCnj8rzxnzq7/tJYRjj t9Q2rUYSrWhJFiNZlxbwRsYWnpQFtLDHkPvgS8/fHPFGz291JOoxOtUGt/uKl2kDwgufe 4VKIWrt1TcvAHO6ejFbeqwv9jTXEgSEVGo+XjOInYWropn6f7+DSmwCj3KRwN7nXAcli4 W2k7kW7dy/v7oQEOPcFRH+QuNk7k24hmqL42f7DCXoKOCQ2bXDijoDqkqS8oIQal2p4Ea K0IcOMUN19Ff5NEbd1pQVuibzXb2UNSnUaRLbVm+d8v0wfO+q1chBRpb9KHcFTwJpUA== ARC-Message-Signature: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; c=relaxed/relaxed; t=1794015907; 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=8VhKLiQa+qgSHc2MwBwT5JarahUkxGmCBQ2Ckl4WmaI=; b=FhhmU15LQ/gvxK4NDrjdSKgE4ugYATbOb64L8f2abvQQ6MTbDvVVIUFvojdLAGqYxgXU nHRqUOcJFPFTRECQwVviXyHybmJuWB/yIkQzitxaa0vnTmLhOKEvOmApqcOOErhyRMQVx Anf1fiy32/8+rn3N+YZ0lcBouITxklnUDOqXA5XaQjewK82/lm6WMV4WHu2aMdqehUzCk SEQvfVMD6DaqzkI0mAoyNZVfFLnIO3Xazw08GxHHeE3cTBoxq4Zj9xBZaO8uzoz/lpjuC IkNUUluKffdoeTSeFTkMZqGkQq44avhfWGCndzmsaUkQm9tjN+ckyEYeprxI7hB1eIQ== 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=Tbph6roN; 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 9C09D606EEA9; Sat, 7 Nov 2026 01:45:06 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.4.2 smtp.subspace.kernel.org 9C09D606EEA9 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, unprotected) header.d=efficios.com header.i=@efficios.com header.a=rsa-sha256 header.s=smtpout1 header.b=Tbph6roN DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=efficios.com; s=smtpout1; t=1794015905; bh=8VhKLiQa+qgSHc2MwBwT5JarahUkxGmCBQ2Ckl4WmaI=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=Tbph6roNO8XSbXZ129PsTSKd3RLjsA0Iw9l0X42fNzOIe+D+m9v4z1tM2ms+K6ytU HGEAqPiZ9xCa8/s1bYNp9n665a3BhOPXLQnuO6+8GinUK9vsAJZAEwSCDwwwjdLuKT D6QcqCNJPHmJc2DMsBiCqlG4So6+ViWpv5onnhx2DVYA/FhB9A0rJz9Ttwz71c30Hw r9dRCRfZqrXcrvaX6RasfXt1ESplMdy8wYGsg+KnaXwM/2aKHgVqaTAThWTerQ2DsI X+0NL6bWUDzSr/jt7M6yQ9l6Fp2Mn0qwpmtmdjK2+M4acSa5cSwex2MMtcgISpjkNf cBC2NoWNwL2pA== Received: from thinkos.internal.efficios.com (unknown [64.58.40.251]) by smtpout.efficios.com (Postfix) with ESMTPSA id 4jLzPs4h7szMFH; Fri, 06 Nov 2026 20:45:05 -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 v4 18/26] cgroup/cpuset: Wait for an attach before rebuilding the sched domains Date: Fri, 6 Nov 2026 20:44:43 -0500 Message-Id: <20261107014451.1487825-19-mathieu.desnoyers@efficios.com> X-Mailer: git-send-email 2.39.5 In-Reply-To: <20261107014451.1487825-1-mathieu.desnoyers@efficios.com> References: <20261107014451.1487825-1-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 cpuset_can_attach() sets aside, in the destination's root domain, the bandwidth of the deadline tasks it is about to move, and drops cpuset_mutex until cpuset_attach() moves them. A rebuild of the sched domains in between, from a write of sched_rt_runtime_us or from the energy model, takes cpuset_mutex, clears the root domains and counts each task where its cpuset says: the reservation is gone. The attach then moves each task's bandwidth on the strength of it, and the destination's total_bw ends short of what its tasks hold: it admits deadline tasks beyond its capacity, and underflows when they leave. The writes of a cpuset's files wait for an attach in progress, wait_attach_done_lock(), since commit 75f7a25ec6bb ("cgroup/cpuset: Prevent race between task attach and cpuset state change"), and CPU hotplug holds cpus_write_lock, which an attach holds for reading throughout. Wait in rebuild_sched_domains_cpuslocked() as well, where a rebuild from hotplug finds no attach in progress, and in cpuset_full_lock(), which the cgroup v1 writes of sched_load_balance and sched_relax_domain_level and hk_sd_workfn() rebuild under, in the order the writes of cpus and cpus.partition take it. The other rebuilds, at the online, offline and kill of a cpuset, run under cgroup_mutex, which the attach holds throughout. The move_vs_rebuild case of deadline_bw_test, added later in this series, moves a process of 2049 threads, the last a deadline task asleep, in and out of a one-CPU partition root while sched_rt_runtime_us is written 20 times, 5ms apart, six rounds. Without this patch a round fails in 5 VMs of 8, the partition root left admitting no task at all, or the other CPUs admitting 3 deadline tasks of 10% more than they have room for; with it, it passes in 8 of 8. A rebuild later in the attach does no harm until the next patch gives back what an attach did not move: it would then give back a reservation already gone. Found by the Sashiko AI review of the second posting of this series, the cgroup v1 writes by that of the third. Fixes: 2ef269ef1ac0 ("cgroup/cpuset: Free DL BW in case can_attach() fails") Cc: stable@vger.kernel.org Signed-off-by: Mathieu Desnoyers --- kernel/cgroup/cpuset.c | 14 +++++++++++--- 1 file changed, 11 insertions(+), 3 deletions(-) diff --git a/kernel/cgroup/cpuset.c b/kernel/cgroup/cpuset.c index bf9a7f88c0ed..2ee58d46da0e 100644 --- a/kernel/cgroup/cpuset.c +++ b/kernel/cgroup/cpuset.c @@ -296,17 +296,19 @@ void lockdep_assert_cpuset_lock_held(void) lockdep_assert_held(&cpuset_mutex); } +static void wait_attach_done_lock(void) __acquires(&cpuset_mutex); + /** * cpuset_full_lock - Acquire full protection for cpuset modification * * Takes both CPU hotplug read lock (cpus_read_lock()) and cpuset mutex - * to safely modify cpuset data. + * to safely modify cpuset data, the latter once no attach is in progress. */ void cpuset_full_lock(void) { mutex_lock(&cpuset_top_mutex); cpus_read_lock(); - mutex_lock(&cpuset_mutex); + wait_attach_done_lock(); } void cpuset_full_unlock(void) @@ -1005,7 +1007,13 @@ void rebuild_sched_domains_locked(void) static void rebuild_sched_domains_cpuslocked(void) { - mutex_lock(&cpuset_mutex); + /* + * An attach in progress has set aside, in the root domain its tasks + * move to, the deadline bandwidth it moves once it takes + * cpuset_mutex again: the rebuild of the accounting would drop that + * reservation, and the move would go through on its strength. + */ + wait_attach_done_lock(); rebuild_sched_domains_locked(); mutex_unlock(&cpuset_mutex); } -- 2.47.3