The patch titled
cgroups: add a per-subsystem hierarchy_mutex
has been removed from the -mm tree. Its filename was
cgroups-add-a-per-subsystem-hierarchy_mutex.patch
This patch was dropped because it was merged into mainline or a subsystem tree
The current -mm tree may be found at http://userweb.kernel.org/~akpm/mmotm/
------------------------------------------------------
Subject: cgroups: add a per-subsystem hierarchy_mutex
From: Paul Menage <menage@xxxxxxxxxx>
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@xxxxxxxxxx>
Tested-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@xxxxxxxxxxxxxx>
Cc: Li Zefan <lizf@xxxxxxxxxxxxxx>
Cc: Balbir Singh <balbir@xxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
Documentation/cgroups/cgroups.txt | 2 -
include/linux/cgroup.h | 17 ++++++++++++
kernel/cgroup.c | 37 ++++++++++++++++++++++++++--
3 files changed, 52 insertions(+), 4 deletions(-)
diff -puN Documentation/cgroups/cgroups.txt~cgroups-add-a-per-subsystem-hierarchy_mutex Documentation/cgroups/cgroups.txt
--- a/Documentation/cgroups/cgroups.txt~cgroups-add-a-per-subsystem-hierarchy_mutex
+++ a/Documentation/cgroups/cgroups.txt
@@ -528,7 +528,7 @@ example in cpusets, no task may attach b
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
diff -puN include/linux/cgroup.h~cgroups-add-a-per-subsystem-hierarchy_mutex include/linux/cgroup.h
--- a/include/linux/cgroup.h~cgroups-add-a-per-subsystem-hierarchy_mutex
+++ a/include/linux/cgroup.h
@@ -340,8 +340,23 @@ struct cgroup_subsys {
#define MAX_CGROUP_TYPE_NAMELEN 32
const char *name;
+ /*
+ * Protects sibling/children links of cgroups in this
+ * hierarchy, plus protects which hierarchy (or none) the
+ * subsystem is a part of (i.e. root/sibling). To avoid
+ * potential deadlocks, the following operations should not be
+ * undertaken while holding any hierarchy_mutex:
+ *
+ * - allocating memory
+ * - initiating hotplug events
+ */
+ struct mutex hierarchy_mutex;
+
+ /*
+ * Link to parent, and list entry in parent's children.
+ * Protected by this->hierarchy_mutex and cgroup_lock()
+ */
struct cgroupfs_root *root;
-
struct list_head sibling;
};
diff -puN kernel/cgroup.c~cgroups-add-a-per-subsystem-hierarchy_mutex kernel/cgroup.c
--- a/kernel/cgroup.c~cgroups-add-a-per-subsystem-hierarchy_mutex
+++ a/kernel/cgroup.c
@@ -722,23 +722,26 @@ static int rebind_subsystems(struct cgro
BUG_ON(cgrp->subsys[i]);
BUG_ON(!dummytop->subsys[i]);
BUG_ON(dummytop->subsys[i]->cgroup != dummytop);
+ mutex_lock(&ss->hierarchy_mutex);
cgrp->subsys[i] = dummytop->subsys[i];
cgrp->subsys[i]->cgroup = cgrp;
list_move(&ss->sibling, &root->subsys_list);
ss->root = root;
if (ss->bind)
ss->bind(ss, cgrp);
-
+ mutex_unlock(&ss->hierarchy_mutex);
} else if (bit & removed_bits) {
/* We're removing this subsystem */
BUG_ON(cgrp->subsys[i] != dummytop->subsys[i]);
BUG_ON(cgrp->subsys[i]->cgroup != cgrp);
+ mutex_lock(&ss->hierarchy_mutex);
if (ss->bind)
ss->bind(ss, dummytop);
dummytop->subsys[i]->cgroup = dummytop;
cgrp->subsys[i] = NULL;
subsys[i]->root = &rootnode;
list_move(&ss->sibling, &rootnode.subsys_list);
+ mutex_unlock(&ss->hierarchy_mutex);
} else if (bit & final_bits) {
/* Subsystem state should already exist */
BUG_ON(!cgrp->subsys[i]);
@@ -2338,6 +2341,29 @@ static void init_cgroup_css(struct cgrou
cgrp->subsys[ss->subsys_id] = css;
}
+static void cgroup_lock_hierarchy(struct cgroupfs_root *root)
+{
+ /* We need to take each hierarchy_mutex in a consistent order */
+ int i;
+
+ for (i = 0; i < CGROUP_SUBSYS_COUNT; i++) {
+ struct cgroup_subsys *ss = subsys[i];
+ if (ss->root == root)
+ mutex_lock_nested(&ss->hierarchy_mutex, i);
+ }
+}
+
+static void cgroup_unlock_hierarchy(struct cgroupfs_root *root)
+{
+ int i;
+
+ for (i = 0; i < CGROUP_SUBSYS_COUNT; i++) {
+ struct cgroup_subsys *ss = subsys[i];
+ if (ss->root == root)
+ mutex_unlock(&ss->hierarchy_mutex);
+ }
+}
+
/*
* cgroup_create - create a cgroup
* @parent: cgroup that will be parent of the new cgroup
@@ -2386,7 +2412,9 @@ static long cgroup_create(struct cgroup
init_cgroup_css(css, ss, cgrp);
}
+ cgroup_lock_hierarchy(root);
list_add(&cgrp->sibling, &cgrp->parent->children);
+ cgroup_unlock_hierarchy(root);
root->number_of_cgroups++;
err = cgroup_create_dir(cgrp, dentry, mode);
@@ -2504,8 +2532,12 @@ static int cgroup_rmdir(struct inode *un
if (!list_empty(&cgrp->release_list))
list_del(&cgrp->release_list);
spin_unlock(&release_list_lock);
- /* delete my sibling from parent->children */
+
+ cgroup_lock_hierarchy(cgrp->root);
+ /* delete this cgroup from parent->children */
list_del(&cgrp->sibling);
+ cgroup_unlock_hierarchy(cgrp->root);
+
spin_lock(&cgrp->dentry->d_lock);
d = dget(cgrp->dentry);
spin_unlock(&d->d_lock);
@@ -2547,6 +2579,7 @@ static void __init cgroup_init_subsys(st
* need to invoke fork callbacks here. */
BUG_ON(!list_empty(&init_task.tasks));
+ mutex_init(&ss->hierarchy_mutex);
ss->active = 1;
}
_
Patches currently in -mm which might be from menage@xxxxxxxxxx are
origin.patch
add-a-refcount-check-in-dput.patch
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