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authorPaul Menage <menage@google.com>2009-01-07 18:08:36 -0800
committerLinus Torvalds <torvalds@linux-foundation.org>2009-01-08 08:31:10 -0800
commit999cd8a450f8f93701669a61cac4d3b19eca07e8 (patch)
tree990e5b08e6db971d2e9943f89abf39e7c8f4cb1e /Documentation
parentb5a84319a4343a0db753436fd8147e61eaafa7ea (diff)
cgroups: add a per-subsystem hierarchy_mutex
These patches introduce new locking/refcount support for cgroups to reduce the need for subsystems to call cgroup_lock(). This will ultimately allow the atomicity of cgroup_rmdir() (which was removed recently) to be restored. These three patches give: 1/3 - introduce a per-subsystem hierarchy_mutex which a subsystem can use to prevent changes to its own cgroup tree 2/3 - use hierarchy_mutex in place of calling cgroup_lock() in the memory controller 3/3 - introduce a css_tryget() function similar to the one recently proposed by Kamezawa, but avoiding spurious refcount failures in the event of a race between a css_tryget() and an unsuccessful cgroup_rmdir() Future patches will likely involve: - using hierarchy mutex in place of cgroup_lock() in more subsystems where appropriate - restoring the atomicity of cgroup_rmdir() with respect to cgroup_create() This patch: Add a hierarchy_mutex to the cgroup_subsys object that protects changes to the hierarchy observed by that subsystem. It is taken by the cgroup subsystem (in addition to cgroup_mutex) for the following operations: - linking a cgroup into that subsystem's cgroup tree - unlinking a cgroup from that subsystem's cgroup tree - moving the subsystem to/from a hierarchy (including across the bind() callback) Thus if the subsystem holds its own hierarchy_mutex, it can safely traverse its own hierarchy. Signed-off-by: Paul Menage <menage@google.com> Tested-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com> Cc: Li Zefan <lizf@cn.fujitsu.com> Cc: Balbir Singh <balbir@in.ibm.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'Documentation')
-rw-r--r--Documentation/cgroups/cgroups.txt2
1 files changed, 1 insertions, 1 deletions
diff --git a/Documentation/cgroups/cgroups.txt b/Documentation/cgroups/cgroups.txt
index 60287e9e9d2..e33ee74eee7 100644
--- a/Documentation/cgroups/cgroups.txt
+++ b/Documentation/cgroups/cgroups.txt
@@ -528,7 +528,7 @@ example in cpusets, no task may attach before 'cpus' and 'mems' are set
up.
void bind(struct cgroup_subsys *ss, struct cgroup *root)
-(cgroup_mutex held by caller)
+(cgroup_mutex and ss->hierarchy_mutex held by caller)
Called when a cgroup subsystem is rebound to a different hierarchy
and root cgroup. Currently this will only involve movement between