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authorLai Jiangshan <laijs@cn.fujitsu.com>2009-01-07 18:07:39 -0800
committerLinus Torvalds <torvalds@linux-foundation.org>2009-01-08 08:31:02 -0800
commit77efecd9e0526327548152df715ab8644ecb5ba0 (patch)
tree4dd2a82fe5db454fb018e434e07c3e6f30dc9832
parent104cbd55377029e70fc2cee01089e84b9c36e5dc (diff)
cgroups: call find_css_set() safely in cgroup_attach_task()
In cgroup_attach_task(), tsk maybe exit when we call find_css_set(). and find_css_set() will access to invalid css_set. This patch increases the count before get_css_set(), and decreases it after find_css_set(). NOTE: css_set's refcount is also taskcount, after this patch applied, taskcount may be off-by-one WHEN cgroup_lock() is not held. but I reviewed other code which use taskcount, they are still correct. No regression found by reviewing and simply testing. So I do not use two counters in css_set. (one counter for taskcount, the other for refcount. like struct mm_struct) If this fix cause regression, we will use two counters in css_set. Signed-off-by: Lai Jiangshan <laijs@cn.fujitsu.com> Cc: Paul Menage <menage@google.com> Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com> Cc: Pavel Emelyanov <xemul@openvz.org> Cc: Balbir Singh <balbir@in.ibm.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
-rw-r--r--kernel/cgroup.c7
1 files changed, 6 insertions, 1 deletions
diff --git a/kernel/cgroup.c b/kernel/cgroup.c
index 00d5136d38c..61e92c5867e 100644
--- a/kernel/cgroup.c
+++ b/kernel/cgroup.c
@@ -1214,7 +1214,7 @@ int cgroup_attach_task(struct cgroup *cgrp, struct task_struct *tsk)
int retval = 0;
struct cgroup_subsys *ss;
struct cgroup *oldcgrp;
- struct css_set *cg = tsk->cgroups;
+ struct css_set *cg;
struct css_set *newcg;
struct cgroupfs_root *root = cgrp->root;
int subsys_id;
@@ -1234,11 +1234,16 @@ int cgroup_attach_task(struct cgroup *cgrp, struct task_struct *tsk)
}
}
+ task_lock(tsk);
+ cg = tsk->cgroups;
+ get_css_set(cg);
+ task_unlock(tsk);
/*
* Locate or allocate a new css_set for this task,
* based on its final set of cgroups
*/
newcg = find_css_set(cg, cgrp);
+ put_css_set(cg);
if (!newcg)
return -ENOMEM;