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

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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
This commit is contained in:
Linus Torvalds 2012-10-24 16:35:13 -07:00
commit cbb525b447
1 changed files with 10 additions and 31 deletions
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41
kernel/cgroup.c
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@ -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);
}
}