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Received: from [2601:18c:8100:a0e0:5a47:caff:fe78:8708] (helo=fangorn) by shelob.surriel.com with esmtpsa (TLS1.3) tls TLS_AES_256_GCM_SHA384 (Exim 4.99.5) (envelope-from ) id 1x00ir-000000093Tk-0mpH; Fri, 28 Aug 2026 17:50:37 +0000 Date: Fri, 28 Aug 2026 13:50:36 -0400 From: Rik van Riel To: linux-kernel@vger.kernel.org Cc: Johannes Weiner , Michal Hocko , Roman Gushchin , Shakeel Butt , Muchun Song , Andrew Morton , cgroups@vger.kernel.org, linux-mm@kvack.org, kernel-team@meta.com Subject: [PATCH v2] mm/memcontrol: fix stuck FLUSHING_CACHED_CHARGE bit on isolated cpus Message-ID: <20260828135036.7d44361f@fangorn> X-Mailer: Claws Mail 4.4.0 (GTK 3.24.52; x86_64-redhat-linux-gnu) MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit X-Stat-Signature: yszfjsah5xjxnp84ts5mg9b46s9od83o X-Rspamd-Server: rspam09 X-Rspamd-Queue-Id: 412F8100007 X-Rspam-User: X-HE-Tag: 1787939466-400204 X-HE-Meta: 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 KfuXZ86J Z6G41Oqn4w74k7XN1kLD2oDrZf/84SSrmIKLJtuSPWHZB/jHFiOXvPbwJTQN0FMZR3t58XW6d+huBe+MVgODajCYVoHbO0u8qwUhXlW2mseRPjDgx4nmtcQHTXdZX7uE6WCdq9DNwvqag1rdE7qGJrwHit9aKxMDTI+BH+aUTYyXOewTb/X2qA48SjA3nY3dNMPJW58cofamlL8NDmmrVcMz/JMgD5zctVgmmaCpIq4HlnMH3qzgQ3nMsL833l7clO6+YAyQBPvgut7RQ/vzJYXCDiApl2WJc90wD3nQ/nY9SnarE+akl8aggJmOFjzdpiiYt+HEjWLTYoBwrFghK/sgM1jbiWWxMHmd1Dyc3eBIYl9iygoen5eH558+lyq8CmiqDLxLuKNUntNmPsI8PNoRIXjvqVdIcXrQsMQZAoMPEQ7Mk44o6aV12MmgAshKMMc6cOZj3FlO7DJUpykGV9B6mUA== Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: When drain_all_stock() sets FLUSHING_CACHED_CHARGE before checking isolation, schedule_drain_work() can drop the work in a separate RCU critical section, and housekeeping_update()'s synchronize_rcu() can race that second check, leaving the flag set. drain_local_stock() only clears the bit for work that ran, so the flag remains set and the stock is never drained again. Have schedule_drain_work() return whether the work was queued, and clear FLUSHING_CACHED_CHARGE in drain_all_stock() when the remote CPU is isolated, so future drains can retry. Fixes: 6a792697a53a ("memcg: do not drain charge pcp caches on remote isolated cpus") Cc: stable@vger.kernel.org Suggested-by: Michal Hocko Suggested-by: Shakeel Butt Signed-off-by: Rik van Riel --- v2: use the approach suggested by Michal and Shakeel Link: https://lore.kernel.org/all/cover.1787890328.git.riel@surriel.com/ mm/memcontrol.c | 19 ++++++++++++------- 1 file changed, 12 insertions(+), 7 deletions(-) diff --git a/mm/memcontrol.c b/mm/memcontrol.c index 1271d390b617..309398e943ca 100644 --- a/mm/memcontrol.c +++ b/mm/memcontrol.c @@ -2306,7 +2306,7 @@ 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) { /* * Protect housekeeping cpumask read and work enqueue together @@ -2315,8 +2315,11 @@ 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)) + return false; + + queue_work_on(cpu, memcg_wq, work); + return true; } /* @@ -2348,8 +2351,9 @@ 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) && @@ -2358,8 +2362,9 @@ 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(); -- 2.55.0