Messages in this thread Patch in this message | | | Date | Mon, 28 Sep 2009 18:13:10 +0900 | From | KAMEZAWA Hiroyuki <> | Subject | [PATCH][rc1] cgroup: catch bad css refcnt at css_put |
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This is a patch for checking css->refcnt's sanity at css_put().
BTW, I noticed that...css->refcnt may overflow if used with memcg... Now, refcnt is incremented per a page. Paul, do you have any idea ? (Ah, yes. "don't use css->refcnt per page" is maybe reasonable but it will be big change..)
== __css_put() doesn't check a bug as refcnt goes to minus. I think it should be caught. This patch adds a check for it.
Signed-off-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com> --- kernel/cgroup.c | 5 ++++- 1 file changed, 4 insertions(+), 1 deletion(-)
Index: linux-2.6.32-rc1/kernel/cgroup.c =================================================================== --- linux-2.6.32-rc1.orig/kernel/cgroup.c +++ linux-2.6.32-rc1/kernel/cgroup.c @@ -3708,8 +3708,10 @@ static void check_for_release(struct cgr void __css_put(struct cgroup_subsys_state *css) { struct cgroup *cgrp = css->cgroup; + int val; rcu_read_lock(); - if (atomic_dec_return(&css->refcnt) == 1) { + val = atomic_dec_return(&css->refcnt); + if (val == 1) { if (notify_on_release(cgrp)) { set_bit(CGRP_RELEASABLE, &cgrp->flags); check_for_release(cgrp); @@ -3717,6 +3719,7 @@ void __css_put(struct cgroup_subsys_stat cgroup_wakeup_rmdir_waiter(cgrp); } rcu_read_unlock(); + WARN_ON(val < 1); } /*
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