[PATCH] mm, memcg: fix mem_cgroup_swapout() for THPs

[PATCH] mm, memcg: fix mem_cgroup_swapout() for THPs

[Shakeel Butt]

The commit d6810d730022 ("memcg, THP, swap: make mem_cgroup_swapout()
support THP") changed mem_cgroup_swapout() to support transparent huge
page (THP). However the patch missed one location which should be
changed for correctly handling THPs. The resulting bug will cause the
memory cgroups whose THPs were swapped out to become zombies on
deletion.

Fixes: d6810d730022 ("memcg, THP, swap: make mem_cgroup_swapout() support THP")
Signed-off-by: Shakeel Butt <shakeelb@google.com>
Cc: stable@vger.kernel.org
---
 mm/memcontrol.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 50e6906314f8..ac2ffd5e02b9 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -6044,7 +6044,7 @@ void mem_cgroup_swapout(struct page *page, swp_entry_t entry)
 	memcg_check_events(memcg, page);
 
 	if (!mem_cgroup_is_root(memcg))
-		css_put(&memcg->css);
+		css_put_many(&memcg->css, nr_entries);
 }
 
 /**
-- 
2.15.0.417.g466bffb3ac-goog

Re: [PATCH] mm, memcg: fix mem_cgroup_swapout() for THPs

[Michal Hocko]

On Tue 28-11-17 08:19:41, Shakeel Butt wrote:
> The commit d6810d730022 ("memcg, THP, swap: make mem_cgroup_swapout()
> support THP") changed mem_cgroup_swapout() to support transparent huge
> page (THP). However the patch missed one location which should be
> changed for correctly handling THPs. The resulting bug will cause the
> memory cgroups whose THPs were swapped out to become zombies on
> deletion.

Very well spotted! Have you seen this triggering or you found it by the
code inspection?

> Fixes: d6810d730022 ("memcg, THP, swap: make mem_cgroup_swapout() support THP")

To be honest I am not really happy how the whole THP swapout thing has
been rushed in without a proper review. I am partly guildy for not find
time for the proper review but this is not something that really had to
be merged without a single ack or reviewed-by.

> Signed-off-by: Shakeel Butt <shakeelb@google.com>
> Cc: stable@vger.kernel.org

Acked-by: Michal Hocko <mhocko@suse.com>

Thanks!

> ---
>  mm/memcontrol.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/mm/memcontrol.c b/mm/memcontrol.c
> index 50e6906314f8..ac2ffd5e02b9 100644
> --- a/mm/memcontrol.c
> +++ b/mm/memcontrol.c
> @@ -6044,7 +6044,7 @@ void mem_cgroup_swapout(struct page *page, swp_entry_t entry)
>  	memcg_check_events(memcg, page);
>  
>  	if (!mem_cgroup_is_root(memcg))
> -		css_put(&memcg->css);
> +		css_put_many(&memcg->css, nr_entries);
>  }
>  
>  /**
> -- 
> 2.15.0.417.g466bffb3ac-goog

-- 
Michal Hocko
SUSE Labs

Re: [PATCH] mm, memcg: fix mem_cgroup_swapout() for THPs

[Shakeel Butt]

On Tue, Nov 28, 2017 at 12:00 PM, Michal Hocko <mhocko@kernel.org> wrote:
> On Tue 28-11-17 08:19:41, Shakeel Butt wrote:
>> The commit d6810d730022 ("memcg, THP, swap: make mem_cgroup_swapout()
>> support THP") changed mem_cgroup_swapout() to support transparent huge
>> page (THP). However the patch missed one location which should be
>> changed for correctly handling THPs. The resulting bug will cause the
>> memory cgroups whose THPs were swapped out to become zombies on
>> deletion.
>
> Very well spotted! Have you seen this triggering or you found it by the
> code inspection?
>

By code inspection.

Re: [PATCH] mm, memcg: fix mem_cgroup_swapout() for THPs

[Huang, Ying]

Shakeel Butt <shakeelb@google.com> writes:

> The commit d6810d730022 ("memcg, THP, swap: make mem_cgroup_swapout()
> support THP") changed mem_cgroup_swapout() to support transparent huge
> page (THP). However the patch missed one location which should be
> changed for correctly handling THPs. The resulting bug will cause the
> memory cgroups whose THPs were swapped out to become zombies on
> deletion.

Good catch!  Thanks a lot for fixing!

Best Regards,
Huang, Ying

> Fixes: d6810d730022 ("memcg, THP, swap: make mem_cgroup_swapout() support THP")
> Signed-off-by: Shakeel Butt <shakeelb@google.com>
> Cc: stable@vger.kernel.org
> ---
>  mm/memcontrol.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/mm/memcontrol.c b/mm/memcontrol.c
> index 50e6906314f8..ac2ffd5e02b9 100644
> --- a/mm/memcontrol.c
> +++ b/mm/memcontrol.c
> @@ -6044,7 +6044,7 @@ void mem_cgroup_swapout(struct page *page, swp_entry_t entry)
>  	memcg_check_events(memcg, page);
>  
>  	if (!mem_cgroup_is_root(memcg))
> -		css_put(&memcg->css);
> +		css_put_many(&memcg->css, nr_entries);
>  }
>  
>  /**

Re: [PATCH] mm, memcg: fix mem_cgroup_swapout() for THPs

[Johannes Weiner]

On Tue, Nov 28, 2017 at 08:19:41AM -0800, Shakeel Butt wrote:
> The commit d6810d730022 ("memcg, THP, swap: make mem_cgroup_swapout()
> support THP") changed mem_cgroup_swapout() to support transparent huge
> page (THP). However the patch missed one location which should be
> changed for correctly handling THPs. The resulting bug will cause the
> memory cgroups whose THPs were swapped out to become zombies on
> deletion.
> 
> Fixes: d6810d730022 ("memcg, THP, swap: make mem_cgroup_swapout() support THP")
> Signed-off-by: Shakeel Butt <shakeelb@google.com>
> Cc: stable@vger.kernel.org

Acked-by: Johannes Weiner <hannes@cmpxchg.org>