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[67.188.127.15]) by smtp.gmail.com with ESMTPSA id 41be03b00d2f7-b270808b57esm6965582a12.75.2025.05.21.18.32.08 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 21 May 2025 18:32:09 -0700 (PDT) From: JP Kobryn To: tj@kernel.org, klarasmodin@gmail.com, shakeel.butt@linux.dev, yosryahmed@google.com, mkoutny@suse.com, hannes@cmpxchg.org, akpm@linux-foundation.org Cc: linux-mm@kvack.org, cgroups@vger.kernel.org, kernel-team@meta.com Subject: [PATCH cgroup/for-6.16] cgroup: avoid per-cpu allocation of size zero rstat cpu locks Date: Wed, 21 May 2025 18:32:02 -0700 Message-ID: <20250522013202.185523-1-inwardvessel@gmail.com> X-Mailer: git-send-email 2.49.0 Precedence: bulk X-Mailing-List: cgroups@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Subsystem rstat locks are dynamically allocated per-cpu. It was discovered that a panic can occur during this allocation when the lock size is zero. This is the case on non-smp systems, since arch_spinlock_t is defined as an empty struct. Prevent this allocation when !CONFIG_SMP by adding a pre-processor conditional around the affected block. Signed-off-by: JP Kobryn Reported-by: Klara Modin Fixes: 748922dcfabd ("cgroup: use subsystem-specific rstat locks to avoid contention") --- kernel/cgroup/rstat.c | 9 +++++++++ 1 file changed, 9 insertions(+) diff --git a/kernel/cgroup/rstat.c b/kernel/cgroup/rstat.c index 7dd396ae3c68..ce4752ab9e09 100644 --- a/kernel/cgroup/rstat.c +++ b/kernel/cgroup/rstat.c @@ -510,11 +510,20 @@ int __init ss_rstat_init(struct cgroup_subsys *ss) { int cpu; +#ifdef CONFIG_SMP + /* + * On uniprocessor machines, arch_spinlock_t is defined as an empty + * struct. Avoid allocating a size of zero by having this block + * excluded in this case. It's acceptable to leave the subsystem locks + * unitialized since the associated lock functions are no-ops in the + * non-smp case. + */ if (ss) { ss->rstat_ss_cpu_lock = alloc_percpu(raw_spinlock_t); if (!ss->rstat_ss_cpu_lock) return -ENOMEM; } +#endif spin_lock_init(ss_rstat_lock(ss)); for_each_possible_cpu(cpu) -- 2.47.1