memcg: fix css_id() RCU locking for real
Commit ad4ba37537
("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>
This commit is contained in:
committed by
Linus Torvalds
parent
11cad320a4
commit
7f0f154641
@ -4435,7 +4435,15 @@ __setup("cgroup_disable=", cgroup_disable);
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*/
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unsigned short css_id(struct cgroup_subsys_state *css)
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{
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struct css_id *cssid = rcu_dereference(css->id);
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struct css_id *cssid;
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/*
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* This css_id() can return correct value when somone has refcnt
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* on this or this is under rcu_read_lock(). Once css->id is allocated,
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* it's unchanged until freed.
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*/
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cssid = rcu_dereference_check(css->id,
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rcu_read_lock_held() || atomic_read(&css->refcnt));
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if (cssid)
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return cssid->id;
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@ -4445,7 +4453,10 @@ EXPORT_SYMBOL_GPL(css_id);
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unsigned short css_depth(struct cgroup_subsys_state *css)
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{
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struct css_id *cssid = rcu_dereference(css->id);
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struct css_id *cssid;
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cssid = rcu_dereference_check(css->id,
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rcu_read_lock_held() || atomic_read(&css->refcnt));
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if (cssid)
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return cssid->depth;
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