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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> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: 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> 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