diff options
| author | KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com> | 2010-05-11 14:06:58 -0700 |
|---|---|---|
| committer | Linus Torvalds <torvalds@linux-foundation.org> | 2010-05-11 17:33:42 -0700 |
| commit | 7f0f15464185a92f9d8791ad231bcd7bf6df54e4 (patch) | |
| tree | a1d4f4c39632659497963b0ccf62828237478d72 | |
| parent | 11cad320a4f4bc53d3585c85600c782faa12b99e (diff) | |
memcg: fix css_id() RCU locking for real
Commit ad4ba375373937817404fd92239ef4cadbded23b ("memcg: css_id() must be
called under rcu_read_lock()") modifies memcontol.c for fixing RCU check
message. But Andrew Morton pointed out that the fix doesn't seems sane
and it was just for hidining lockdep messages.
This is a patch for do proper things. Checking again, all places,
accessing without rcu_read_lock, that commit fixies was intentional....
all callers of css_id() has reference count on it. So, it's not necessary
to be under rcu_read_lock().
Considering again, we can use rcu_dereference_check for css_id(). We know
css->id is valid if css->refcnt > 0. (css->id never changes and freed
after css->refcnt going to be 0.)
This patch makes use of rcu_dereference_check() in css_id/depth and remove
unnecessary rcu-read-lock added by the commit.
Signed-off-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
Cc: Daisuke Nishimura <nishimura@mxp.nes.nec.co.jp>
Cc: Balbir Singh <balbir@linux.vnet.ibm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
| -rw-r--r-- | kernel/cgroup.c | 15 | ||||
| -rw-r--r-- | mm/memcontrol.c | 19 |
2 files changed, 18 insertions, 16 deletions
diff --git a/kernel/cgroup.c b/kernel/cgroup.c index 3a53c771e50..6db8b7f297a 100644 --- a/kernel/cgroup.c +++ b/kernel/cgroup.c @@ -4435,7 +4435,15 @@ __setup("cgroup_disable=", cgroup_disable); */ unsigned short css_id(struct cgroup_subsys_state *css) { - struct css_id *cssid = rcu_dereference(css->id); + struct css_id *cssid; + + /* + * This css_id() can return correct value when somone has refcnt + * on this or this is under rcu_read_lock(). Once css->id is allocated, + * it's unchanged until freed. + */ + cssid = rcu_dereference_check(css->id, + rcu_read_lock_held() || atomic_read(&css->refcnt)); if (cssid) return cssid->id; @@ -4445,7 +4453,10 @@ EXPORT_SYMBOL_GPL(css_id); unsigned short css_depth(struct cgroup_subsys_state *css) { - struct css_id *cssid = rcu_dereference(css->id); + struct css_id *cssid; + + cssid = rcu_dereference_check(css->id, + rcu_read_lock_held() || atomic_read(&css->refcnt)); if (cssid) return cssid->depth; diff --git a/mm/memcontrol.c b/mm/memcontrol.c index 0f711c213d2..595d03f33b2 100644 --- a/mm/memcontrol.c +++ b/mm/memcontrol.c @@ -2314,9 +2314,7 @@ mem_cgroup_uncharge_swapcache(struct page *page, swp_entry_t ent, bool swapout) /* record memcg information */ if (do_swap_account && swapout && memcg) { - rcu_read_lock(); swap_cgroup_record(ent, css_id(&memcg->css)); - rcu_read_unlock(); mem_cgroup_get(memcg); } if (swapout && memcg) @@ -2373,10 +2371,8 @@ static int mem_cgroup_move_swap_account(swp_entry_t entry, { unsigned short old_id, new_id; - rcu_read_lock(); old_id = css_id(&from->css); new_id = css_id(&to->css); - rcu_read_unlock(); if (swap_cgroup_cmpxchg(entry, old_id, new_id) == old_id) { mem_cgroup_swap_statistics(from, false); @@ -4044,16 +4040,11 @@ static int is_target_pte_for_mc(struct vm_area_struct *vma, put_page(page); } /* throught */ - if (ent.val && do_swap_account && !ret) { - unsigned short id; - rcu_read_lock(); - id = css_id(&mc.from->css); - rcu_read_unlock(); - if (id == lookup_swap_cgroup(ent)) { - ret = MC_TARGET_SWAP; - if (target) - target->ent = ent; - } + if (ent.val && do_swap_account && !ret && + css_id(&mc.from->css) == lookup_swap_cgroup(ent)) { + ret = MC_TARGET_SWAP; + if (target) + target->ent = ent; } return ret; } |