Commit 68744676 authored Nov 12, 2008 by Li Zefan Committed by Linus Torvalds Nov 12, 2008

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>

parent 0bcb6069

kernel/cgroup_freezer.c

+6 −2

Original line number	Diff line number	Diff line
		@@ -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);

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