Commit cbb525b4 authored by Linus Torvalds's avatar Linus Torvalds
Browse files

Merge branch 'for-3.7-fixes' of git://git.kernel.org/pub/scm/linux/kernel/git/tj/cgroup 

Pull cgroup fixes from Tejun Heo:
 "This pull request contains three fixes.

  Two are reverts of task_lock() removal in cgroup fork path.  The
  optimizations incorrectly assumed that threadgroup_lock can protect
  process forks (as opposed to thread creations) too.  Further cleanup
  of cgroup fork path is scheduled.

  The third fixes cgroup emptiness notification loss."

* 'for-3.7-fixes' of git://git.kernel.org/pub/scm/linux/kernel/git/tj/cgroup:
  Revert "cgroup: Remove task_lock() from cgroup_post_fork()"
  Revert "cgroup: Drop task_lock(parent) on cgroup_fork()"
  cgroup: notify_on_release may not be triggered in some cases
parents d579a35d d8783832

kernel/cgroup.c

+10 −31
Original line number Diff line number Diff line
@@ -1962,9 +1962,8 @@ static void cgroup_task_migrate(struct cgroup *cgrp, struct cgroup *oldcgrp, 
	 * trading it for newcg is protected by cgroup_mutex, we're safe to drop

	 * it here; it will be freed under RCU.

	 */

	put_css_set(oldcg);



	set_bit(CGRP_RELEASABLE, &oldcgrp->flags);

	put_css_set(oldcg);

}



/**
@@ -4815,31 +4814,20 @@ static const struct file_operations proc_cgroupstats_operations = { 
 *

 * A pointer to the shared css_set was automatically copied in

 * fork.c by dup_task_struct().  However, we ignore that copy, since

 * it was not made under the protection of RCU, cgroup_mutex or

 * threadgroup_change_begin(), so it might no longer be a valid

 * cgroup pointer.  cgroup_attach_task() might have already changed

 * current->cgroups, allowing the previously referenced cgroup

 * group to be removed and freed.

 *

 * Outside the pointer validity we also need to process the css_set

 * inheritance between threadgoup_change_begin() and

 * threadgoup_change_end(), this way there is no leak in any process

 * wide migration performed by cgroup_attach_proc() that could otherwise

 * miss a thread because it is too early or too late in the fork stage.

 * it was not made under the protection of RCU or cgroup_mutex, so

 * might no longer be a valid cgroup pointer.  cgroup_attach_task() might

 * have already changed current->cgroups, allowing the previously

 * referenced cgroup group to be removed and freed.

 *

 * At the point that cgroup_fork() is called, 'current' is the parent

 * task, and the passed argument 'child' points to the child task.

 */

void cgroup_fork(struct task_struct *child)

{

	/*

	 * We don't need to task_lock() current because current->cgroups

	 * can't be changed concurrently here. The parent obviously hasn't

	 * exited and called cgroup_exit(), and we are synchronized against

	 * cgroup migration through threadgroup_change_begin().

	 */

	task_lock(current);

	child->cgroups = current->cgroups;

	get_css_set(child->cgroups);

	task_unlock(current);

	INIT_LIST_HEAD(&child->cg_list);

}
@@ -4895,19 +4883,10 @@ void cgroup_post_fork(struct task_struct *child) 
	 */

	if (use_task_css_set_links) {

		write_lock(&css_set_lock);

		if (list_empty(&child->cg_list)) {

			/*

			 * It's safe to use child->cgroups without task_lock()

			 * here because we are protected through

			 * threadgroup_change_begin() against concurrent

			 * css_set change in cgroup_task_migrate(). Also

			 * the task can't exit at that point until

			 * wake_up_new_task() is called, so we are protected

			 * against cgroup_exit() setting child->cgroup to

			 * init_css_set.

			 */

		task_lock(child);

		if (list_empty(&child->cg_list))

			list_add(&child->cg_list, &child->cgroups->tasks);

		}

		task_unlock(child);

		write_unlock(&css_set_lock);

	}

}

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