Messages in this thread | | | Date | Thu, 11 Dec 2008 09:37:33 +0900 | From | KAMEZAWA Hiroyuki <> | Subject | Re: [RFC][PATCH 1/3] CGroups: Add a per-subsystem hierarchy_mutex |
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thank you for this work.
On Wed, 10 Dec 2008 15:36:55 -0800 menage@google.com 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 <menage@google.com> > > --- > > 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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