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authorTejun Heo <tj@kernel.org>2014-05-16 21:22:49 +0400
committerTejun Heo <tj@kernel.org>2014-05-16 21:22:49 +0400
commitde3f034182ecbf0efbcef7ab8b253c6c3049a592 (patch)
treeff49be5f6dbccf13c40d9ee1eff41cd8a0ab3cd8 /include/linux/cgroup.h
parent0cb51d71c1fa9234afe4213089844be76ec1765a (diff)
downloadlinux-de3f034182ecbf0efbcef7ab8b253c6c3049a592.tar.xz
cgroup: introduce CSS_RELEASED and reduce css iteration fallback window
css iterations allow the caller to drop RCU read lock. As long as the caller keeps the current position accessible, it can simply re-grab RCU read lock later and continue iteration. This is achieved by using CGRP_DEAD to detect whether the current positions next pointer is safe to dereference and if not re-iterate from the beginning to the next position using ->serial_nr. CGRP_DEAD is used as the marker to invalidate the next pointer and the only requirement is that the marker is set before the next sibling starts its RCU grace period. Because CGRP_DEAD is set at the end of cgroup_destroy_locked() but the cgroup is unlinked when the reference count reaches zero, we currently have a rather large window where this fallback re-iteration logic can be triggered. This patch introduces CSS_RELEASED which is set when a css is unlinked from its sibling list. This still keeps the re-iteration logic working while drastically reducing the window of its activation. While at it, rewrite the comment in css_next_child() to reflect the new flag and better explain the synchronization. This will also enable iterating csses directly instead of through cgroups. v2: CSS_RELEASED now assigned to 1 << 2 as 1 << 0 is used by CSS_NO_REF. Signed-off-by: Tejun Heo <tj@kernel.org> Acked-by: Li Zefan <lizefan@huawei.com>
Diffstat (limited to 'include/linux/cgroup.h')
-rw-r--r--include/linux/cgroup.h1
1 files changed, 1 insertions, 0 deletions
diff --git a/include/linux/cgroup.h b/include/linux/cgroup.h
index ebe7ce49f4b7..5375582ea5f6 100644
--- a/include/linux/cgroup.h
+++ b/include/linux/cgroup.h
@@ -97,6 +97,7 @@ struct cgroup_subsys_state {
enum {
CSS_NO_REF = (1 << 0), /* no reference counting for this css */
CSS_ONLINE = (1 << 1), /* between ->css_online() and ->css_offline() */
+ CSS_RELEASED = (1 << 2), /* refcnt reached zero, released */
};
/**