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Diffstat (limited to 'kernel/cgroup.c')
-rw-r--r--kernel/cgroup.c57
1 files changed, 23 insertions, 34 deletions
diff --git a/kernel/cgroup.c b/kernel/cgroup.c
index 145deeb69bc3..ad447684aa47 100644
--- a/kernel/cgroup.c
+++ b/kernel/cgroup.c
@@ -386,10 +386,22 @@ static void free_css_set_work(struct work_struct *work)
struct cgroup *cgrp = link->cgrp;
list_del(&link->cg_link_list);
list_del(&link->cgrp_link_list);
- if (atomic_dec_and_test(&cgrp->count)) {
+
+
+ /*
+ * We may not be holding cgroup_mutex, and if cgrp->count is
+ * dropped to 0 the cgroup can be destroyed at any time, hence
+ * rcu_read_lock is used to keep it alive.
+ */
+ rcu_read_lock();
+ if (atomic_dec_and_test(&cgrp->count) &&
+ notify_on_release(cgrp)) {
check_for_release(cgrp);
cgroup_wakeup_rmdir_waiter(cgrp);
}
+
+ rcu_read_unlock();
+
kfree(link);
}
write_unlock(&css_set_lock);
@@ -1878,9 +1890,8 @@ 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);
}
/**
@@ -2623,9 +2634,7 @@ static int cgroup_create_dir(struct cgroup *cgrp, struct dentry *dentry,
dentry->d_fsdata = cgrp;
inc_nlink(parent->d_inode);
rcu_assign_pointer(cgrp->dentry, dentry);
- dget(dentry);
}
- dput(dentry);
return error;
}
@@ -4533,31 +4542,20 @@ 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);
}
@@ -4610,19 +4608,10 @@ 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);
}
}