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Mon, 26 Jul 2021 08:00:21 -0700 (PDT) Received: from localhost ([2620:10d:c091:480::1:e732]) by smtp.gmail.com with ESMTPSA id h10sm99931qka.83.2021.07.26.08.00.20 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 26 Jul 2021 08:00:20 -0700 (PDT) From: Johannes Weiner To: Andrew Morton Cc: Dan Carpenter , linux-mm@kvack.org, cgroups@vger.kernel.org, linux-kernel@vger.kernel.org, kernel-team@fb.com Subject: [PATCH] mm: memcontrol: fix blocking rstat function called from atomic cgroup1 thresholding code Date: Mon, 26 Jul 2021 11:00:19 -0400 Message-Id: <20210726150019.251820-1-hannes@cmpxchg.org> X-Mailer: git-send-email 2.32.0 MIME-Version: 1.0 Authentication-Results: imf12.hostedemail.com; dkim=pass header.d=cmpxchg-org.20150623.gappssmtp.com header.s=20150623 header.b=ZXLe+pV1; spf=pass (imf12.hostedemail.com: domain of hannes@cmpxchg.org designates 209.85.160.174 as permitted sender) smtp.mailfrom=hannes@cmpxchg.org; dmarc=pass (policy=none) header.from=cmpxchg.org X-Rspamd-Server: rspam02 X-Stat-Signature: wg9fbt6kea46qs9s9gp8n8crhtqwf569 X-Rspamd-Queue-Id: 049A31000C87 X-HE-Tag: 1627311621-401411 Content-Transfer-Encoding: quoted-printable X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: Dan Carpenter reports: The patch 2d146aa3aa84: "mm: memcontrol: switch to rstat" from Apr 29, 2021, leads to the following static checker warning: kernel/cgroup/rstat.c:200 cgroup_rstat_flush() warn: sleeping in atomic context mm/memcontrol.c 3572 static unsigned long mem_cgroup_usage(struct mem_cgroup *memc= g, bool swap) 3573 { 3574 unsigned long val; 3575 3576 if (mem_cgroup_is_root(memcg)) { 3577 cgroup_rstat_flush(memcg->css.cgroup); ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ This is from static analysis and potentially a false positive. The problem is that mem_cgroup_usage() is called from __mem_cgroup_thresh= old() which holds an rcu_read_lock(). And the cgroup_rstat_flush() functio= n can sleep. 3578 val =3D memcg_page_state(memcg, NR_FILE_PAGES= ) + 3579 memcg_page_state(memcg, NR_ANON_MAPPE= D); 3580 if (swap) 3581 val +=3D memcg_page_state(memcg, MEMC= G_SWAP); 3582 } else { 3583 if (!swap) 3584 val =3D page_counter_read(&memcg->mem= ory); 3585 else 3586 val =3D page_counter_read(&memcg->mem= sw); 3587 } 3588 return val; 3589 } __mem_cgroup_threshold() indeed holds the rcu lock. In addition, the thresholding code is invoked during stat changes, and those contexts have irqs disabled as well. If the lock breaking occurs inside the flush function, it will result in a sleep from an atomic context. Use the irsafe flushing variant in mem_cgroup_usage() to fix this. Fixes: 2d146aa3aa84 ("mm: memcontrol: switch to rstat") Cc: Reported-by: Dan Carpenter Signed-off-by: Johannes Weiner --- mm/memcontrol.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-) diff --git a/mm/memcontrol.c b/mm/memcontrol.c index ae1f5d0cb581..eb8e87c4833f 100644 --- a/mm/memcontrol.c +++ b/mm/memcontrol.c @@ -3574,7 +3574,8 @@ static unsigned long mem_cgroup_usage(struct mem_cg= roup *memcg, bool swap) unsigned long val; =20 if (mem_cgroup_is_root(memcg)) { - cgroup_rstat_flush(memcg->css.cgroup); + /* mem_cgroup_threshold() calls here from irqsafe context */ + cgroup_rstat_flush_irqsafe(memcg->css.cgroup); val =3D memcg_page_state(memcg, NR_FILE_PAGES) + memcg_page_state(memcg, NR_ANON_MAPPED); if (swap) --=20 2.32.0