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    Subject[PATCH 2/9] cgroup: Use rculist ops for cgroup->children
    Date
    Use RCU safe list operations for cgroup->children.  This will be used
    to implement cgroup children / descendant walking which can be used by
    controllers.

    Note that cgroup_create() now puts a new cgroup at the end of the
    ->children list instead of head. This isn't strictly necessary but is
    done so that the iteration order is more conventional.

    Signed-off-by: Tejun Heo <tj@kernel.org>
    ---
    include/linux/cgroup.h | 1 +
    kernel/cgroup.c | 8 +++-----
    2 files changed, 4 insertions(+), 5 deletions(-)

    diff --git a/include/linux/cgroup.h b/include/linux/cgroup.h
    index b442122..90c33eb 100644
    --- a/include/linux/cgroup.h
    +++ b/include/linux/cgroup.h
    @@ -12,6 +12,7 @@
    #include <linux/cpumask.h>
    #include <linux/nodemask.h>
    #include <linux/rcupdate.h>
    +#include <linux/rculist.h>
    #include <linux/cgroupstats.h>
    #include <linux/prio_heap.h>
    #include <linux/rwsem.h>
    diff --git a/kernel/cgroup.c b/kernel/cgroup.c
    index f05d992..cc5d2a0 100644
    --- a/kernel/cgroup.c
    +++ b/kernel/cgroup.c
    @@ -1650,7 +1650,6 @@ static struct dentry *cgroup_mount(struct file_system_type *fs_type,

    free_cg_links(&tmp_cg_links);

    - BUG_ON(!list_empty(&root_cgrp->sibling));
    BUG_ON(!list_empty(&root_cgrp->children));
    BUG_ON(root->number_of_cgroups != 1);

    @@ -1699,7 +1698,6 @@ static void cgroup_kill_sb(struct super_block *sb) {

    BUG_ON(root->number_of_cgroups != 1);
    BUG_ON(!list_empty(&cgrp->children));
    - BUG_ON(!list_empty(&cgrp->sibling));

    mutex_lock(&cgroup_mutex);
    mutex_lock(&cgroup_root_mutex);
    @@ -4053,7 +4051,7 @@ static long cgroup_create(struct cgroup *parent, struct dentry *dentry,
    }
    }

    - list_add(&cgrp->sibling, &cgrp->parent->children);
    + list_add_tail_rcu(&cgrp->sibling, &cgrp->parent->children);
    root->number_of_cgroups++;

    err = cgroup_create_dir(cgrp, dentry, mode);
    @@ -4084,7 +4082,7 @@ static long cgroup_create(struct cgroup *parent, struct dentry *dentry,

    err_remove:

    - list_del(&cgrp->sibling);
    + list_del_rcu(&cgrp->sibling);
    root->number_of_cgroups--;

    err_destroy:
    @@ -4210,7 +4208,7 @@ static int cgroup_rmdir(struct inode *unused_dir, struct dentry *dentry)
    raw_spin_unlock(&release_list_lock);

    /* delete this cgroup from parent->children */
    - list_del_init(&cgrp->sibling);
    + list_del_rcu(&cgrp->sibling);

    list_del_init(&cgrp->allcg_node);

    --
    1.7.11.7


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