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Date: Thu, 11 Dec 2008 12:00:20 +0530 From: Balbir Singh <balbir@...ux.vnet.ibm.com> To: KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com> Cc: menage@...gle.com, containers@...ts.linux-foundation.org, linux-kernel@...r.kernel.org, akpm@...ux-foundation.org Subject: Re: [RFC][PATCH 1/3] CGroups: Add a per-subsystem hierarchy_mutex * KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com> [2008-12-11 09:37:33]: > thank you for this work. > > On Wed, 10 Dec 2008 15:36:55 -0800 > menage@...gle.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@...gle.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--) ? > Good point! -- Balbir -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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