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[109.81.85.229]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-49c5a903eebsm17011155e9.4.2026.08.28.07.25.42 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 28 Aug 2026 07:25:43 -0700 (PDT) Date: Fri, 28 Aug 2026 16:25:41 +0200 From: Michal Hocko To: Rik van Riel Cc: linux-kernel@vger.kernel.org, Johannes Weiner , Roman Gushchin , Shakeel Butt , Muchun Song , Andrew Morton , cgroups@vger.kernel.org, linux-mm@kvack.org, kernel-team@meta.com, stable@vger.kernel.org Subject: Re: [PATCH] mm/memcontrol: avoid stuck FLUSHING_CACHED_CHARGE bit on isolated cpus Message-ID: References: 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=us-ascii Content-Disposition: inline In-Reply-To: On Fri 28-08-26 09:46:21, Rik van Riel wrote: > drain_all_stock() can leave FLUSHING_CACHED_CHARGE set after the > work is dropped. It sets the bit before checking isolation and > schedule_drain_work() checks isolation and queues in a separate RCU > critical section, so housekeeping_update()'s synchronize_rcu() can > race the second check. > > drain_local_stock() only clears the bit for work that ran, so the bit > remains set and the stock is never drained again. > > Reorganize the drain_all_stock() loop, reducing nesting, splitting > out local vs remote cpu handling, and skipping everything on isolated > cpus, which solves the stuck FLUSHING_CACHED_CHARGE flag. Is there any reason why we cannot simply clear the flag if the work is not scheduled? --- diff --git a/mm/memcontrol.c b/mm/memcontrol.c index 69b37f63a307..907ac63e5067 100644 --- a/mm/memcontrol.c +++ b/mm/memcontrol.c @@ -2261,8 +2261,10 @@ static bool is_memcg_drain_needed(struct memcg_stock_pcp *stock, return flush; } -static void schedule_drain_work(int cpu, struct work_struct *work) +static bool schedule_drain_work(int cpu, struct work_struct *work) { + int ret = false; + /* * Protect housekeeping cpumask read and work enqueue together * in the same RCU critical section so that later cpuset isolated @@ -2270,8 +2272,12 @@ static void schedule_drain_work(int cpu, struct work_struct *work) * pending work on newly isolated CPUs. */ guard(rcu)(); - if (!cpu_is_isolated(cpu)) - queue_work_on(cpu, memcg_wq, work); + if (!cpu_is_isolated(cpu)) { + queue_work_on(cpu, memcg_wq, &memcg_st->work); + ret = true; + } + + return ret; } /* @@ -2303,8 +2309,8 @@ void drain_all_stock(struct mem_cgroup *root_memcg) &memcg_st->flags)) { if (cpu == curcpu) drain_local_memcg_stock(&memcg_st->work); - else - schedule_drain_work(cpu, &memcg_st->work); + else if (!schedule_drain_work(cpu, &memcg_st->work)) + clear_bit(FLUSHING_CACHED_CHARGE, &memcg_st->flags) } if (!test_bit(FLUSHING_CACHED_CHARGE, &obj_st->flags) && @@ -2313,8 +2319,8 @@ void drain_all_stock(struct mem_cgroup *root_memcg) &obj_st->flags)) { if (cpu == curcpu) drain_local_obj_stock(&obj_st->work); - else - schedule_drain_work(cpu, &obj_st->work); + else if (!schedule_drain_work(cpu, &obj_st->work)) + clear_bit(FLUSHING_CACHED_CHARGE, &obj_st->flags); } } migrate_enable(); -- Michal Hocko SUSE Labs