Messages in this thread Patch in this message | | | Date | Wed, 10 Dec 2008 15:33:12 -0800 | Subject | [PATCH] CGroups: Fix a race between rmdir and remount | From | Paul Menage <> |
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Fix a race between rmdir and remount
When a cgroup is removed, it's unlinked from its parent's children list, but not actually freed until the last dentry on it is released (at which point cgrp->root->number_of_cgroups is decremented).
Currently rebind_subsystems checks for the top cgroup's child list being empty in order to rebind subsystems into or out of a hierarchy - this can result in the set of subsystems bound to a hierarchy being different than the set of subsystems with state in the removed-but-not-freed cgroup.
The simplest fix for this is to forbid remounts that change the set of subsystems on a hierarchy that has removed-but-not-freed cgroups.
This bug can be reproduced via:
mkdir /mnt/cg mount -t cgroup -o ns,freezer cgroup /mnt/cg mkdir /mnt/cg/foo sleep 1h < /mnt/cg/foo & rmdir /mnt/cg/foo mount -t cgroup -o remount,ns,devices,freezer cgroup /mnt/cg kill $!
Signed-off-by: Paul Menage <menage@google.com>
--- kernel/cgroup.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)
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 @@ -702,7 +702,7 @@ static int rebind_subsystems(struct cgro * any child cgroups exist. This is theoretically supportable * but involves complex error handling, so it's being left until * later */ - if (!list_empty(&cgrp->children)) + if (root->number_of_cgroups > 1) return -EBUSY;
/* Process each subsystem */
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