* Re: [PATCH] mm: memcontrol: fix blocking rstat function called from atomic cgroup1 thresholding code
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
2021-07-26 15:16 ` Rik van Riel
` (2 subsequent siblings)
3 siblings, 0 replies; 7+ messages in thread
From: Chris Down @ 2021-07-26 15:08 UTC (permalink / raw)
To: Johannes Weiner
Cc: Andrew Morton, Dan Carpenter, linux-mm, cgroups, linux-kernel,
kernel-team
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
>
>
^ permalink raw reply [flat|nested] 7+ messages in thread* Re: [PATCH] mm: memcontrol: fix blocking rstat function called from atomic cgroup1 thresholding code
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
@ 2021-07-26 15:16 ` Rik van Riel
2021-07-27 16:51 ` Shakeel Butt
2021-07-26 20:32 ` Michal Hocko
2021-07-27 16:59 ` Shakeel Butt
3 siblings, 1 reply; 7+ messages in thread
From: Rik van Riel @ 2021-07-26 15:16 UTC (permalink / raw)
To: hannes, akpm; +Cc: Kernel Team, dan.carpenter, linux-mm, linux-kernel, cgroups
On Mon, 2021-07-26 at 11:00 -0400, Johannes Weiner wrote:
>
> __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
While this fix is necessary, in the long term I think we may
want some sort of redesign here, to make sure the irq safe
version does not spin long times trying to get the statistics
off some other CPU.
I have seen a number of soft (IIRC) lockups deep inside the
bowels of cgroup_rstat_flush_irqsafe, with the function taking
multiple seconds to complete.
Reviewed-by: Rik van Riel <riel@surriel.com>
^ permalink raw reply [flat|nested] 7+ messages in thread
* Re: [PATCH] mm: memcontrol: fix blocking rstat function called from atomic cgroup1 thresholding code
2021-07-26 15:16 ` Rik van Riel
@ 2021-07-27 16:51 ` Shakeel Butt
2021-08-03 14:34 ` Rik van Riel
0 siblings, 1 reply; 7+ messages in thread
From: Shakeel Butt @ 2021-07-27 16:51 UTC (permalink / raw)
To: Rik van Riel
Cc: hannes, akpm, Kernel Team, dan.carpenter, linux-mm, linux-kernel,
cgroups
On Mon, Jul 26, 2021 at 8:19 AM Rik van Riel <riel@fb.com> wrote:
>
> On Mon, 2021-07-26 at 11:00 -0400, Johannes Weiner wrote:
> >
> > __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
>
> While this fix is necessary, in the long term I think we may
> want some sort of redesign here, to make sure the irq safe
> version does not spin long times trying to get the statistics
> off some other CPU.
>
> I have seen a number of soft (IIRC) lockups deep inside the
> bowels of cgroup_rstat_flush_irqsafe, with the function taking
> multiple seconds to complete.
Can you please share a bit more detail on this lockup? I am wondering
if this was due to the flush not happening more often and thus the
update tree is large or if there are too many concurrent flushes
happening.
>
> Reviewed-by: Rik van Riel <riel@surriel.com>
^ permalink raw reply [flat|nested] 7+ messages in thread
* Re: [PATCH] mm: memcontrol: fix blocking rstat function called from atomic cgroup1 thresholding code
2021-07-27 16:51 ` Shakeel Butt
@ 2021-08-03 14:34 ` Rik van Riel
0 siblings, 0 replies; 7+ messages in thread
From: Rik van Riel @ 2021-08-03 14:34 UTC (permalink / raw)
To: shakeelb
Cc: Kernel Team, dan.carpenter, hannes, cgroups, linux-mm,
linux-kernel, akpm
On Tue, 2021-07-27 at 09:51 -0700, Shakeel Butt wrote:
> On Mon, Jul 26, 2021 at 8:19 AM Rik van Riel <riel@fb.com> wrote:
> >
> > On Mon, 2021-07-26 at 11:00 -0400, Johannes Weiner wrote:
> > >
> > > __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
> >
> > While this fix is necessary, in the long term I think we may
> > want some sort of redesign here, to make sure the irq safe
> > version does not spin long times trying to get the statistics
> > off some other CPU.
> >
> > I have seen a number of soft (IIRC) lockups deep inside the
> > bowels of cgroup_rstat_flush_irqsafe, with the function taking
> > multiple seconds to complete.
>
> Can you please share a bit more detail on this lockup? I am wondering
> if this was due to the flush not happening more often and thus the
> update tree is large or if there are too many concurrent flushes
> happening.
I was not logged into any system while it happened, but
only found it later in the logs.
I suspect your explanation is the reason why it happened,
though.
^ permalink raw reply [flat|nested] 7+ messages in thread
* Re: [PATCH] mm: memcontrol: fix blocking rstat function called from atomic cgroup1 thresholding code
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
2021-07-26 15:16 ` Rik van Riel
@ 2021-07-26 20:32 ` Michal Hocko
2021-07-27 16:59 ` Shakeel Butt
3 siblings, 0 replies; 7+ messages in thread
From: Michal Hocko @ 2021-07-26 20:32 UTC (permalink / raw)
To: Johannes Weiner
Cc: Andrew Morton, Dan Carpenter, linux-mm, cgroups, linux-kernel,
kernel-team
On Mon 26-07-21 11:00:19, Johannes Weiner wrote:
> 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>
Acked-by: Michal Hocko <mhocko@suse.com>
Thanks!
> ---
> 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
--
Michal Hocko
SUSE Labs
^ permalink raw reply [flat|nested] 7+ messages in thread* Re: [PATCH] mm: memcontrol: fix blocking rstat function called from atomic cgroup1 thresholding code
2021-07-26 15:00 [PATCH] mm: memcontrol: fix blocking rstat function called from atomic cgroup1 thresholding code Johannes Weiner
` (2 preceding siblings ...)
2021-07-26 20:32 ` Michal Hocko
@ 2021-07-27 16:59 ` Shakeel Butt
3 siblings, 0 replies; 7+ messages in thread
From: Shakeel Butt @ 2021-07-27 16:59 UTC (permalink / raw)
To: Johannes Weiner
Cc: Andrew Morton, Dan Carpenter, Linux MM, Cgroups, LKML, Kernel Team
On Mon, Jul 26, 2021 at 8:01 AM Johannes Weiner <hannes@cmpxchg.org> wrote:
>
> 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>
Reviewed-by: Shakeel Butt <shakeelb@google.com>
BTW what do you think of removing stat flushes from the read side
(kernel and userspace) completely after periodic flushing and async
flushing from update side? Basically with "memcg: infrastructure to
flush memcg stats".
^ permalink raw reply [flat|nested] 7+ messages in thread