2014-10-23 14:33:57

by Johannes Weiner

Subject: [patch] mm: memcontrol: don't pass a NULL memcg to mem_cgroup_end_move()

mem_cgroup_end_move() checks if the passed memcg is NULL, along with a
lengthy comment to explain why this seemingly non-sensical situation
is even possible.

Check in cancel_attach() itself whether can_attach() set up the move
context or not, it's a lot more obvious from there. Then remove the
check and comment in mem_cgroup_end_move().

Signed-off-by: Johannes Weiner <[email protected]>
Acked-by: Vladimir Davydov <[email protected]>
---
mm/memcontrol.c | 10 +++-------
1 file changed, 3 insertions(+), 7 deletions(-)

diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index a5c9aa4688e8..3cd4f1e0bfb3 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -1469,12 +1469,7 @@ static void mem_cgroup_start_move(struct mem_cgroup *memcg)

static void mem_cgroup_end_move(struct mem_cgroup *memcg)
{
- /*
- * Now, mem_cgroup_clear_mc() may call this function with NULL.
- * We check NULL in callee rather than caller.
- */
- if (memcg)
- atomic_dec(&memcg->moving_account);
+ atomic_dec(&memcg->moving_account);
}

/*
@@ -5489,7 +5484,8 @@ static int mem_cgroup_can_attach(struct cgroup_subsys_state *css,
static void mem_cgroup_cancel_attach(struct cgroup_subsys_state *css,
struct cgroup_taskset *tset)
{
- mem_cgroup_clear_mc();
+ if (mc.to)
+ mem_cgroup_clear_mc();
}

static int mem_cgroup_move_charge_pte_range(pmd_t *pmd,
--
2.1.2

2014-10-23 15:13:23

by Michal Hocko

Subject: Re: [patch] mm: memcontrol: don't pass a NULL memcg to mem_cgroup_end_move()

On Thu 23-10-14 10:33:50, Johannes Weiner wrote:
> mem_cgroup_end_move() checks if the passed memcg is NULL, along with a
> lengthy comment to explain why this seemingly non-sensical situation
> is even possible.
>
> Check in cancel_attach() itself whether can_attach() set up the move
> context or not, it's a lot more obvious from there. Then remove the
> check and comment in mem_cgroup_end_move().
>
> Signed-off-by: Johannes Weiner <[email protected]>
> Acked-by: Vladimir Davydov <[email protected]>

Acked-by: Michal Hocko <[email protected]>

> ---
> mm/memcontrol.c | 10 +++-------
> 1 file changed, 3 insertions(+), 7 deletions(-)
>
> diff --git a/mm/memcontrol.c b/mm/memcontrol.c
> index a5c9aa4688e8..3cd4f1e0bfb3 100644
> --- a/mm/memcontrol.c
> +++ b/mm/memcontrol.c
> @@ -1469,12 +1469,7 @@ static void mem_cgroup_start_move(struct mem_cgroup *memcg)
>
> static void mem_cgroup_end_move(struct mem_cgroup *memcg)
> {
> - /*
> - * Now, mem_cgroup_clear_mc() may call this function with NULL.
> - * We check NULL in callee rather than caller.
> - */
> - if (memcg)
> - atomic_dec(&memcg->moving_account);
> + atomic_dec(&memcg->moving_account);
> }
>
> /*
> @@ -5489,7 +5484,8 @@ static int mem_cgroup_can_attach(struct cgroup_subsys_state *css,
> static void mem_cgroup_cancel_attach(struct cgroup_subsys_state *css,
> struct cgroup_taskset *tset)
> {
> - mem_cgroup_clear_mc();
> + if (mc.to)
> + mem_cgroup_clear_mc();
> }
>
> static int mem_cgroup_move_charge_pte_range(pmd_t *pmd,
> --
> 2.1.2
>

--
Michal Hocko
SUSE Labs