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authorLi Zefan <lizf@cn.fujitsu.com>2008-11-12 13:26:49 -0800
committerLinus Torvalds <torvalds@linux-foundation.org>2008-11-12 17:17:16 -0800
commit687446760bd008df96655cb8c5900f8e48a7118c (patch)
treeb4834a1e88d98234cfad90a0880b54ba1cc3cc59
parent0bcb6069a6e1af5c114a2a8873ec43ada8933596 (diff)
freezer_cg: remove task_lock from freezer_fork()
In theory the task can be moved to another cgroup and the freezer will be freed right after task_lock is dropped, so the lock results in zero protection. But in the case of freezer_fork() no lock is needed, since the task is not in tasklist yet so it won't be moved to another cgroup, so task->cgroups won't be changed or invalidated. Signed-off-by: Li Zefan <lizf@cn.fujitsu.com> Cc: Matt Helsley <matthltc@us.ibm.com> Cc: Cedric Le Goater <clg@fr.ibm.com> Cc: "Serge E. Hallyn" <serue@us.ibm.com> Cc: Paul Menage <menage@google.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
-rw-r--r--kernel/cgroup_freezer.c8
1 files changed, 6 insertions, 2 deletions
diff --git a/kernel/cgroup_freezer.c b/kernel/cgroup_freezer.c
index 7fa476f01d05..660590710409 100644
--- a/kernel/cgroup_freezer.c
+++ b/kernel/cgroup_freezer.c
@@ -184,9 +184,13 @@ static void freezer_fork(struct cgroup_subsys *ss, struct task_struct *task)
{
struct freezer *freezer;
- task_lock(task);
+ /*
+ * No lock is needed, since the task isn't on tasklist yet,
+ * so it can't be moved to another cgroup, which means the
+ * freezer won't be removed and will be valid during this
+ * function call.
+ */
freezer = task_freezer(task);
- task_unlock(task);
spin_lock_irq(&freezer->lock);
BUG_ON(freezer->state == CGROUP_FROZEN);