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Wed, 19 Aug 2026 03:08:12 +0000 X-Migadu-Flow: FLOW_OUT Message-ID: <56052cbe-463d-4dbd-aa43-11f66232680c@linux.dev> Date: Wed, 19 Aug 2026 11:08:00 +0800 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v2] mm/oom_kill: simplify remaining RCU sections with scoped_guard(rcu) To: Michal Hocko Cc: Andrew Morton , Ye Liu , David Rientjes , Shakeel Butt , linux-mm@kvack.org, linux-kernel@vger.kernel.org References: <20260813092933.562028-1-ye.liu@linux.dev> Content-Language: en-US From: Ye Liu In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-Stat-Signature: ze4n3t3gh8ggdoagfdisgfsiaghpfyon X-Rspamd-Queue-Id: 3B674100009 X-Rspam-User: X-Rspamd-Server: rspam12 X-HE-Tag: 1787108905-341550 X-HE-Meta: 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 +XJIGcPB Imh8q8KnP+Gow0CEalf1KmEyTzD/Oleo07Y3651u/P/zWFmR0swhhVCX0hx54jD2mBH5uMUePRHWgxKV3zMLh6kQT61DY5PwvtDugIdGqw8oOv3VkgZBm2tJmsmygbqoxVH17InOmlLuLoAZU3zKoaPCn5hJvZVvpQkMPtK6iyYVMBiz69KJBkZ6vJp7AtYp3NztGayDezTjJsnCTkPPtzIf49TUXmuZIDqmEOjlEMvGHfy9d2AXbiLKsX+uk828CKEJqsUuA8+s13T0LIg1dbctqYFYnsrbN0M9gLcc+xw5x78cI6l9svUANnWFUg5LPludx7UgbCBYutrg8n8ZRypVw9cxNn2Sw4cLqF/jyQ0bByiSd1M7cW5TncMrAfn2w7X/deDAnHhS41l+tuTII6I0lyD46LTLpdjS3KI+NyuT4Qr8= Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: 在 2026/8/13 19:40, Michal Hocko 写道: > 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. > Adding RCU versions of for_each_thread and for_each_process (for_each_thread_rcu and for_each_process_rcu) would be useful. I also have some simplified code to go with them. I'll send a patchset later. Thanks. > 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 > -- Thanks, Ye Liu