* menage@xxxxxxxxxx <menage@xxxxxxxxxx> [2008-12-10 15:36:55]: > 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) > > Thus if the subsystem holds its own hierarchy_mutex, it can safely > traverse its own hierarchy. > Ths sounds reasonable, a further abstraction in the future could be to provide the visitor pattern. Allow cgroups to do the walking and have callbacks called during the visit. > Signed-off-by: Paul Menage <menage@xxxxxxxxxx> > > --- > > 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); > + } > +} > + > /* > * cgroup_create - create a cgroup > * @parent: cgroup that will be parent of the new cgroup > @@ -2374,7 +2400,9 @@ 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); > @@ -2492,8 +2520,12 @@ 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); > @@ -2535,6 +2567,7 @@ 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; > } > > Index: hierarchy_lock-mmotm-2008-12-09/Documentation/cgroups/cgroups.txt > =================================================================== > --- hierarchy_lock-mmotm-2008-12-09.orig/Documentation/cgroups/cgroups.txt > +++ hierarchy_lock-mmotm-2008-12-09/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) > Seems reasonable, I was wondering if instead of acquiring a mutex per subsystem that shares the root, if we can collapse it to a single mutex and prevent cgroup from changing binding. Those are optimizations that we can think of later Acked-by: Balbir Singh <balbir@xxxxxxxxxxxxxxxxxx> -- Balbir _______________________________________________ Containers mailing list Containers@xxxxxxxxxxxxxxxxxxxxxxxxxx https://lists.linux-foundation.org/mailman/listinfo/containers