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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>
This commit is contained in:
Li Zefan 2008-11-12 13:26:49 -08:00 committed by Linus Torvalds
parent 0bcb6069a6
commit 687446760b
1 changed files with 6 additions and 2 deletions
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8
kernel/cgroup_freezer.c
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@ -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);