From: Chris Down <chris@chrisdown.name>
To: Johannes Weiner <hannes@cmpxchg.org>
Cc: Andrew Morton <akpm@linux-foundation.org>,
Dan Carpenter <dan.carpenter@oracle.com>,
linux-mm@kvack.org, cgroups@vger.kernel.org,
linux-kernel@vger.kernel.org, kernel-team@fb.com
Subject: Re: [PATCH] mm: memcontrol: fix blocking rstat function called from atomic cgroup1 thresholding code
Date: Mon, 26 Jul 2021 16:08:54 +0100 [thread overview]
Message-ID: <YP7QBuc+5gAlL4g7@chrisdown.name> (raw)
In-Reply-To: <20210726150019.251820-1-hannes@cmpxchg.org>
Johannes Weiner writes:
>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 *memcg, 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_threshold()
> which holds an rcu_read_lock(). And the cgroup_rstat_flush() function
> can sleep.
>
> 3578 val = memcg_page_state(memcg, NR_FILE_PAGES) +
> 3579 memcg_page_state(memcg, NR_ANON_MAPPED);
> 3580 if (swap)
> 3581 val += memcg_page_state(memcg, MEMCG_SWAP);
> 3582 } else {
> 3583 if (!swap)
> 3584 val = page_counter_read(&memcg->memory);
> 3585 else
> 3586 val = page_counter_read(&memcg->memsw);
> 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: <stable@vger.kernel.org>
>Reported-by: Dan Carpenter <dan.carpenter@oracle.com>
>Signed-off-by: Johannes Weiner <hannes@cmpxchg.org>
Thanks, looks good.
Acked-by: Chris Down <chris@chrisdown.name>
>---
> 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_cgroup *memcg, bool swap)
> unsigned long val;
>
> 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 = memcg_page_state(memcg, NR_FILE_PAGES) +
> memcg_page_state(memcg, NR_ANON_MAPPED);
> if (swap)
>--
>2.32.0
>
>
next prev parent reply other threads:[~2021-07-26 15:08 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-07-26 15:00 [PATCH] mm: memcontrol: fix blocking rstat function called from atomic cgroup1 thresholding code Johannes Weiner
2021-07-26 15:08 ` Chris Down [this message]
2021-07-26 15:16 ` Rik van Riel
2021-07-27 16:51 ` Shakeel Butt
2021-08-03 14:34 ` Rik van Riel
2021-07-26 20:32 ` Michal Hocko
2021-07-27 16:59 ` Shakeel Butt
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