thank you for this work.
On Wed, 10 Dec 2008 15:36:55 -0800
[EMAIL PROTECTED] wrote:
> This patch adds 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)
>
o.k. usage is very clear.
> Thus if the subsystem holds its own hierarchy_mutex, it can safely
> traverse its own hierarchy.
>
> Signed-off-by: Paul Menage <[EMAIL PROTECTED]>
>
> ---
>
> Documentation/cgroups/cgroups.txt | 2 +-
> include/linux/cgroup.h | 9 ++++++++-
> kernel/cgroup.c | 37
> +++++++++++++++++++++++++++++++++++--
> 3 files changed, 44 insertions(+), 4 deletions(-)
>
> Index: hierarchy_lock-mmotm-2008-12-09/include/linux/cgroup.h
> ===================================================================
> --- hierarchy_lock-mmotm-2008-12-09.orig/include/linux/cgroup.h
> +++ hierarchy_lock-mmotm-2008-12-09/include/linux/cgroup.h
> @@ -337,8 +337,15 @@ struct cgroup_subsys {
> #define MAX_CGROUP_TYPE_NAMELEN 32
> const char *name;
>
> - struct cgroupfs_root *root;
> + /*
> + * 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)
> + */
> + struct mutex hierarchy_mutex;
>
> + /* Protected by this->hierarchy_mutex and cgroup_lock() */
> + struct cgroupfs_root *root;
> struct list_head sibling;
> };
>
> Index: hierarchy_lock-mmotm-2008-12-09/kernel/cgroup.c
> ===================================================================
> --- hierarchy_lock-mmotm-2008-12-09.orig/kernel/cgroup.c
> +++ hierarchy_lock-mmotm-2008-12-09/kernel/cgroup.c
> @@ -714,23 +714,26 @@ 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]);
> @@ -2326,6 +2329,29 @@ 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);
> + }
> +}
> +
Maybe no problem..but I don't like releasing lock in the order of acquiring
lock.
for (i = CGROUP_SUBSYS_COUNT - 1; i >=0; i--) ?
-Kame
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