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@xxxxxxxxxxxxxx>
---
kernel/cgroup_freezer.c | 8 ++++++--
1 files changed, 6 insertions(+), 2 deletions(-)
diff --git a/kernel/cgroup_freezer.c b/kernel/cgroup_freezer.c
index 7fa476f..6605907 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);
--
1.5.4.rc3
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