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authorTejun Heo <tj@kernel.org>2012-11-05 09:16:58 -0800
committerTejun Heo <tj@kernel.org>2012-11-05 09:16:58 -0800
commite93160803ffda2e67d9ff9cacb63bb6868c8398f (patch)
treee3305bb56336c32862f1970882f030caca7f11b2 /include/linux/cgroup.h
parented95779340b50e362245c81b5dec0d11a1debfa8 (diff)
cgroup: kill CSS_REMOVED
CSS_REMOVED is one of the several contortions which were necessary to support css reference draining on cgroup removal. All css->refcnts which need draining should be deactivated and verified to equal zero atomically w.r.t. css_tryget(). If any one isn't zero, all refcnts needed to be re-activated and css_tryget() shouldn't fail in the process. This was achieved by letting css_tryget() busy-loop until either the refcnt is reactivated (failed removal attempt) or CSS_REMOVED is set (committing to removal). Now that css refcnt draining is no longer used, there's no need for atomic rollback mechanism. css_tryget() simply can look at the reference count and fail if it's deactivated - it's never getting re-activated. This patch removes CSS_REMOVED and updates __css_tryget() to fail if the refcnt is deactivated. As deactivation and removal are a single step now, they no longer need to be protected against css_tryget() happening from irq context. Remove local_irq_disable/enable() from cgroup_rmdir(). Note that this removes css_is_removed() whose only user is VM_BUG_ON() in memcontrol.c. We can replace it with a check on the refcnt but given that the only use case is a debug assert, I think it's better to simply unexport it. v2: Comment updated and explanation on local_irq_disable/enable() added per Michal Hocko. Signed-off-by: Tejun Heo <tj@kernel.org> Reviewed-by: Michal Hocko <mhocko@suse.cz> Reviewed-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com> Acked-by: Li Zefan <lizefan@huawei.com> Cc: Johannes Weiner <hannes@cmpxchg.org> Cc: Balbir Singh <bsingharora@gmail.com>
Diffstat (limited to 'include/linux/cgroup.h')
-rw-r--r--include/linux/cgroup.h6
1 files changed, 0 insertions, 6 deletions
diff --git a/include/linux/cgroup.h b/include/linux/cgroup.h
index 02e09c0e98ab..a3098046250b 100644
--- a/include/linux/cgroup.h
+++ b/include/linux/cgroup.h
@@ -85,7 +85,6 @@ struct cgroup_subsys_state {
/* bits in struct cgroup_subsys_state flags field */
enum {
CSS_ROOT, /* This CSS is the root of the subsystem */
- CSS_REMOVED, /* This CSS is dead */
};
/* Caller must verify that the css is not for root cgroup */
@@ -108,11 +107,6 @@ static inline void css_get(struct cgroup_subsys_state *css)
__css_get(css, 1);
}
-static inline bool css_is_removed(struct cgroup_subsys_state *css)
-{
- return test_bit(CSS_REMOVED, &css->flags);
-}
-
/*
* Call css_tryget() to take a reference on a css if your existing
* (known-valid) reference isn't already ref-counted. Returns false if