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Commit 68744676 authored by Li Zefan's avatar Li Zefan Committed by Linus Torvalds
Browse files

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: default avatarLi 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: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 0bcb6069

kernel/cgroup_freezer.c

+6 −2
Original line number Original line Diff line number Diff line
@@ -184,9 +184,13 @@ static void freezer_fork(struct cgroup_subsys *ss, struct task_struct *task) 
{

{

	struct freezer *freezer;

	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);

	freezer = task_freezer(task);

	task_unlock(task);





	spin_lock_irq(&freezer->lock);

	spin_lock_irq(&freezer->lock);

	BUG_ON(freezer->state == CGROUP_FROZEN);

	BUG_ON(freezer->state == CGROUP_FROZEN);