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>
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@ -184,9 +184,13 @@ static void freezer_fork(struct cgroup_subsys *ss, struct task_struct *task)
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{
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struct freezer *freezer;
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task_lock(task);
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/*
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* No lock is needed, since the task isn't on tasklist yet,
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* so it can't be moved to another cgroup, which means the
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* freezer won't be removed and will be valid during this
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* function call.
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*/
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freezer = task_freezer(task);
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task_unlock(task);
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spin_lock_irq(&freezer->lock);
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BUG_ON(freezer->state == CGROUP_FROZEN);
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