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b=PXYh6M2KkgQHGOcPs4VHfkvwxJyfSKuED6zAeHwMz8mmUUgtOHTbSiQM5BJieAoLO H/WV7XvvSbkldcw2ezKoX6DKUZtAcjDvgjCWVLh1TbnJnQlGY+u4pRC+AIJ1cr/4s+ JByHYpe+ebHxFnreqVNPxaZ5n/PFOCKp9FCVEt1gVdNWAjj4teAKaCf/xFOIYta2uQ 234zl/9rw3uirz1ArxlCvIIddHjOso0Sf2s3/7xSRv4/CUeZyw0WEXcN1ojHc4WL4H w3jDfaKIq5AcnXo1qggs2ROLMdMYAzKmTRqpoIncaxXUWYTKO89frDEQNSedcwHZs4 lxnBzFqghs4Ig== From: "Vlastimil Babka (SUSE)" Date: Fri, 07 Aug 2026 15:50:31 +0200 Subject: [PATCH RFC 5/5] sched: use kfree_nolock() instead of kfree_rcu() MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: 7bit Message-Id: <20260807-kfree_nolock_kmalloc-v1-5-ba993cbf7a60@kernel.org> References: <20260807-kfree_nolock_kmalloc-v1-0-ba993cbf7a60@kernel.org> In-Reply-To: <20260807-kfree_nolock_kmalloc-v1-0-ba993cbf7a60@kernel.org> To: Harry Yoo , Alexei Starovoitov , Alexander Potapenko , Marco Elver , Sumit Semwal , =?utf-8?q?Christian_K=C3=B6nig?= , Catalin Marinas , Ingo Molnar , Peter Zijlstra , Juri Lelli , Vincent Guittot , Sebastian Andrzej Siewior , Clark Williams , Steven Rostedt Cc: Andrew Morton , Hao Li , Christoph Lameter , David Rientjes , Roman Gushchin , bpf@vger.kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, Dmitry Vyukov , linux-media@vger.kernel.org, dri-devel@lists.freedesktop.org, linaro-mm-sig@lists.linaro.org, kasan-dev@googlegroups.com, Dietmar Eggemann , Ben Segall , Mel Gorman , Valentin Schneider , K Prateek Nayak , linux-rt-devel@lists.linux.dev, "Vlastimil Babka (SUSE)" X-Mailer: b4 0.15.2 X-Rspam-User: X-Rspamd-Server: rspam03 X-Stat-Signature: m3rsup1n154nc57hx6wohiewaephaj7u X-Rspamd-Queue-Id: BD25E40015 X-HE-Tag: 1786110672-483662 X-HE-Meta: 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 AOVWbZAp Hw0Gq+lbHvrYUFeB2FJvn8B3M+dWjG4fmLPCCcCwRiRW/h2JbwAJP1oqbRSUtOMwW83l7W4x2Ujr9aMQtMcOLr4KfcHExHCWYvbC2v7S8OU8miezQOqA55oMcMJ8ZQFoxtbl1ESyh1+zNLlFry2Wd1JBrTVTRjCiGve/pL5Okp1CYj+m70F1rE2goMJHnxTcRtJAWlAOix0ZahvTol4n3pkv1Eo5eCfCDe8Xp7OjKeMBMvCco3RqM049xIa1QEUqOLSmfdlgDc0X0oyeLhx+cEKr7ZIyMlvoxJBfr Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: In set_cpus_allowed_force() we use kfree_rcu() because kfree() is unsafe under p->pi_lock. With kfree_nolock() now being able to free arbitrary kmalloc() objects, we can switch to kfree_nolock() and avoid the unnecessary rcu grace period delay. Only in some cases the freeing might be deferred to irq_work(). Signed-off-by: Vlastimil Babka (SUSE) --- kernel/sched/core.c | 9 ++------- kernel/sched/sched.h | 7 +------ 2 files changed, 3 insertions(+), 13 deletions(-) diff --git a/kernel/sched/core.c b/kernel/sched/core.c index 96226707c2f6..d2929e4e23f1 100644 --- a/kernel/sched/core.c +++ b/kernel/sched/core.c @@ -2807,20 +2807,15 @@ void set_cpus_allowed_force(struct task_struct *p, const struct cpumask *new_mas .user_mask = NULL, .flags = SCA_USER, /* clear the user requested mask */ }; - union cpumask_rcuhead { - cpumask_t cpumask; - struct rcu_head rcu; - }; scoped_guard (__task_rq_lock, p) do_set_cpus_allowed(p, &ac); /* * Because this is called with p->pi_lock held, it is not possible - * to use kfree() here (when PREEMPT_RT=y), therefore punt to using - * kfree_rcu(). + * to use kfree() here (when PREEMPT_RT=y), thus use kfree_nolock() */ - kfree_rcu((union cpumask_rcuhead *)ac.user_mask, rcu); + kfree_nolock(ac.user_mask); } int dup_user_cpus_ptr(struct task_struct *dst, struct task_struct *src, diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h index 56acf502ba26..6a8d0578e963 100644 --- a/kernel/sched/sched.h +++ b/kernel/sched/sched.h @@ -2886,12 +2886,7 @@ static inline bool task_allowed_on_cpu(struct task_struct *p, int cpu) static inline cpumask_t *alloc_user_cpus_ptr(int node) { - /* - * See set_cpus_allowed_force() above for the rcu_head usage. - */ - int size = max_t(int, cpumask_size(), sizeof(struct rcu_head)); - - return kmalloc_node(size, GFP_KERNEL, node); + return kmalloc_node(cpumask_size(), GFP_KERNEL, node); } static inline struct task_struct *get_push_task(struct rq *rq) -- 2.55.0