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[109.81.29.60]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-49982121649sm55382155e9.1.2026.08.13.04.40.52 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 13 Aug 2026 04:40:52 -0700 (PDT) Date: Thu, 13 Aug 2026 13:40:51 +0200 From: Michal Hocko To: Ye Liu Cc: Andrew Morton , Ye Liu , David Rientjes , Shakeel Butt , linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH v2] mm/oom_kill: simplify remaining RCU sections with scoped_guard(rcu) Message-ID: References: <20260813092933.562028-1-ye.liu@linux.dev> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <20260813092933.562028-1-ye.liu@linux.dev> X-Stat-Signature: rnfrsr5bxzc1ej593tfqh37wjhjmi6c8 X-Rspamd-Queue-Id: 11411C0007 X-Rspamd-Server: rspam03 X-Rspam-User: X-HE-Tag: 1786621253-645381 X-HE-Meta: U2FsdGVkX18LdygTVIyc1kwMVazx8uysT80RPdFgqJTqAucaJMt8rKTIVX6DD4YKCuS+lYWZxLmUvNQ0zSBSfrM4v6Jhfh7f02YAsEXv4nMNf90zaLDb7l30VHTcx0EjT1LJlAc0UaZGUHV02/5m9Z9e1m5z72sYai2xiepeH39afSNqU0+CiTKEfC4gN/g165BnNG0CALJRw4K6cnOTxfRNlptNpW7J/Yi/8rkptvG5iBzUPQfY1o5mt/kQz10gObXMpYHUNtkJpwG5u9wnpewi77j+x1BzYz0LuYfSJYb/3XGbzROj6wqV37IO8EYPAhHwq5zAjfHY2Z2Txaw4rbBut8gjPjLh5xpRkqQClTw7xVuoPOrJAVYxBBWeIbfBGN9rKonIhuTBFj2hXAe7XJDEMenLVeYoF6Rj7Bqb6ywTrqHUtANLpJww3+PiVEg0Q4oJIyXFgcxFD5VlYM/4gAFj/2XvXg9mWCK7ARpJsnQzJVViYAb0EmLxO6lWf19CLdGQhbsu1wRR3EY8BlgQk6CltaaXFOagZ5mgF2HKsQDk7mkD4wW0ChDH02g+7hYAc/TI+XDW1+lQe/AwrqwZnvRc0Y4pzahiaE8f1Udx2CSSVOno6o5HrGSy9dGWdu8LB8jmfC8IcuBuMmbX6fLJX7KkYKFJV713k7BafL2AWRoVsf9FXJNz6PSccGFER84cQpFVqbO6iBELqbEwg9e7WI7gwEiMzCVGAWbq6r6r4nrLBYO78O8n8CjJbBe/8gqqC3aub1Jbc2544PYgI/W8PEBI8HC6UCLqtFhBMLG022o43D2YhbCNy2erY7Qedpb4pOSLYi50HEAKWAmP1EGdqty4fIILosVwmA+PfTxO2lVncI+oTXXtSeZm4m0KgTEcZtpF6ti7ymBs4TlqL9ZBxG9aus9ijnOvhmR6o4iPgEuzQyvMB685B6SmA9Jz5g9MhozNuC5PoNFQ2d2jp3o 2Pi5NY2n 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 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Thu 13-08-26 17:29:32, Ye Liu wrote: > From: Ye Liu > > Replace the remaining manual rcu_read_lock()/rcu_read_unlock() pairs > in oom_cpuset_eligible(), select_bad_process(), dump_tasks(), > task_will_free_mem(), and __oom_kill_process() with scoped_guard(rcu) > for consistency and simpler control flow. scoped_guard(rcu) limits > the RCU critical section to the loop body rather than the entire > remaining function scope, making the protected region explicit and > safer for future changes. > > Signed-off-by: Ye Liu It almost looks like for_each_thread and for_each_process could gain an rcu varian that would do the rcu thing internally. Have you considered that? I am pretty sure there will be more cases like these. Anyway Acked-by: Michal Hocko Thanks > --- > v2: > - Use scoped_guard instead of guard. > - Link：https://lore.kernel.org/all/20260813032634.344946-1-ye.liu@linux.dev/ > > mm/oom_kill.c | 124 +++++++++++++++++++++++++------------------------- > 1 file changed, 62 insertions(+), 62 deletions(-) > > diff --git a/mm/oom_kill.c b/mm/oom_kill.c > index 5f372f6e26fa..0e8982e5be51 100644 > --- a/mm/oom_kill.c > +++ b/mm/oom_kill.c > @@ -94,27 +94,27 @@ static bool oom_cpuset_eligible(struct task_struct *start, > bool ret = false; > const nodemask_t *mask = oc->nodemask; > > - rcu_read_lock(); > - for_each_thread(start, tsk) { > - if (mask) { > - /* > - * If this is a mempolicy constrained oom, tsk's > - * cpuset is irrelevant. Only return true if its > - * mempolicy intersects current, otherwise it may be > - * needlessly killed. > - */ > - ret = mempolicy_in_oom_domain(tsk, mask); > - } else { > - /* > - * This is not a mempolicy constrained oom, so only > - * check the mems of tsk's cpuset. > - */ > - ret = cpuset_mems_allowed_intersects(current, tsk); > + scoped_guard(rcu) { > + for_each_thread(start, tsk) { > + if (mask) { > + /* > + * If this is a mempolicy constrained oom, tsk's > + * cpuset is irrelevant. Only return true if its > + * mempolicy intersects current, otherwise it may be > + * needlessly killed. > + */ > + ret = mempolicy_in_oom_domain(tsk, mask); > + } else { > + /* > + * This is not a mempolicy constrained oom, so only > + * check the mems of tsk's cpuset. > + */ > + ret = cpuset_mems_allowed_intersects(current, tsk); > + } > + if (ret) > + break; > } > - if (ret) > - break; > } > - rcu_read_unlock(); > > return ret; > } > @@ -368,11 +368,11 @@ static void select_bad_process(struct oom_control *oc) > else { > struct task_struct *p; > > - rcu_read_lock(); > - for_each_process(p) > - if (oom_evaluate_task(p, oc)) > - break; > - rcu_read_unlock(); > + scoped_guard(rcu) { > + for_each_process(p) > + if (oom_evaluate_task(p, oc)) > + break; > + } > } > } > > @@ -430,14 +430,14 @@ static void dump_tasks(struct oom_control *oc) > struct task_struct *p; > int i = 0; > > - rcu_read_lock(); > - for_each_process(p) { > - /* Avoid potential softlockup warning */ > - if ((++i & 1023) == 0) > - touch_softlockup_watchdog(); > - dump_task(p, oc); > + scoped_guard(rcu) { > + for_each_process(p) { > + /* Avoid potential softlockup warning */ > + if ((++i & 1023) == 0) > + touch_softlockup_watchdog(); > + dump_task(p, oc); > + } > } > - rcu_read_unlock(); > } > } > > @@ -894,17 +894,17 @@ static bool task_will_free_mem(struct task_struct *task) > * are dying as well to make sure that a) nobody pins its mm and > * b) the task is also reapable by the oom reaper. > */ > - rcu_read_lock(); > - for_each_process(p) { > - if (!process_shares_mm(p, mm)) > - continue; > - if (same_thread_group(task, p)) > - continue; > - ret = __task_will_free_mem(p); > - if (!ret) > - break; > + scoped_guard(rcu) { > + for_each_process(p) { > + if (!process_shares_mm(p, mm)) > + continue; > + if (same_thread_group(task, p)) > + continue; > + ret = __task_will_free_mem(p); > + if (!ret) > + break; > + } > } > - rcu_read_unlock(); > > return ret; > } > @@ -960,29 +960,29 @@ static void __oom_kill_process(struct task_struct *victim, const char *message) > * That thread will now get access to memory reserves since it has a > * pending fatal signal. > */ > - rcu_read_lock(); > - for_each_process(p) { > - if (!process_shares_mm(p, mm)) > - continue; > - if (same_thread_group(p, victim)) > - continue; > - if (is_global_init(p)) { > - can_oom_reap = false; > - mm_flags_set(MMF_OOM_SKIP, mm); > - pr_info("oom killer %d (%s) has mm pinned by %d (%s)\n", > - task_pid_nr(victim), victim->comm, > - task_pid_nr(p), p->comm); > - continue; > + scoped_guard(rcu) { > + for_each_process(p) { > + if (!process_shares_mm(p, mm)) > + continue; > + if (same_thread_group(p, victim)) > + continue; > + if (is_global_init(p)) { > + can_oom_reap = false; > + mm_flags_set(MMF_OOM_SKIP, mm); > + pr_info("oom killer %d (%s) has mm pinned by %d (%s)\n", > + task_pid_nr(victim), victim->comm, > + task_pid_nr(p), p->comm); > + continue; > + } > + /* > + * No kthread_use_mm() user needs to read from the userspace so > + * we are ok to reap it. > + */ > + if (unlikely(p->flags & PF_KTHREAD)) > + continue; > + do_send_sig_info(SIGKILL, SEND_SIG_PRIV, p, PIDTYPE_TGID); > } > - /* > - * No kthread_use_mm() user needs to read from the userspace so > - * we are ok to reap it. > - */ > - if (unlikely(p->flags & PF_KTHREAD)) > - continue; > - do_send_sig_info(SIGKILL, SEND_SIG_PRIV, p, PIDTYPE_TGID); > } > - rcu_read_unlock(); > > if (can_oom_reap) > queue_oom_reaper(victim); > -- > 2.25.1 -- Michal Hocko SUSE Labs