Merge branch 'nfs-for-2.6.32'

[pandora-kernel.git] / kernel / cgroup.c

diff --git a/kernel/cgroup.c b/kernel/cgroup.c
index 250dac0..c7ece8f 100644 (file)
--- a/kernel/cgroup.c
+++ b/kernel/cgroup.c
@@ -600,6 +600,7 @@ static struct inode_operations cgroup_dir_inode_operations;
 static struct file_operations proc_cgroupstats_operations;
 
 static struct backing_dev_info cgroup_backing_dev_info = {
+       .name           = "cgroup",
        .capabilities   = BDI_CAP_NO_ACCT_AND_WRITEBACK,
 };
 
@@ -735,16 +736,28 @@ static void cgroup_d_remove_dir(struct dentry *dentry)
  * reference to css->refcnt. In general, this refcnt is expected to goes down
  * to zero, soon.
  *
- * CGRP_WAIT_ON_RMDIR flag is modified under cgroup's inode->i_mutex;
+ * CGRP_WAIT_ON_RMDIR flag is set under cgroup's inode->i_mutex;
  */
 DECLARE_WAIT_QUEUE_HEAD(cgroup_rmdir_waitq);
 
-static void cgroup_wakeup_rmdir_waiters(const struct cgroup *cgrp)
+static void cgroup_wakeup_rmdir_waiter(struct cgroup *cgrp)
 {
-       if (unlikely(test_bit(CGRP_WAIT_ON_RMDIR, &cgrp->flags)))
+       if (unlikely(test_and_clear_bit(CGRP_WAIT_ON_RMDIR, &cgrp->flags)))
                wake_up_all(&cgroup_rmdir_waitq);
 }
 
+void cgroup_exclude_rmdir(struct cgroup_subsys_state *css)
+{
+       css_get(css);
+}
+
+void cgroup_release_and_wakeup_rmdir(struct cgroup_subsys_state *css)
+{
+       cgroup_wakeup_rmdir_waiter(css->cgroup);
+       css_put(css);
+}
+
+
 static int rebind_subsystems(struct cgroupfs_root *root,
                              unsigned long final_bits)
 {
@@ -1359,7 +1372,7 @@ int cgroup_attach_task(struct cgroup *cgrp, struct task_struct *tsk)
         * wake up rmdir() waiter. the rmdir should fail since the cgroup
         * is no longer empty.
         */
-       cgroup_wakeup_rmdir_waiters(cgrp);
+       cgroup_wakeup_rmdir_waiter(cgrp);
        return 0;
 }
 
@@ -2743,34 +2756,43 @@ again:
        }
        mutex_unlock(&cgroup_mutex);
 
+       /*
+        * In general, subsystem has no css->refcnt after pre_destroy(). But
+        * in racy cases, subsystem may have to get css->refcnt after
+        * pre_destroy() and it makes rmdir return with -EBUSY. This sometimes
+        * make rmdir return -EBUSY too often. To avoid that, we use waitqueue
+        * for cgroup's rmdir. CGRP_WAIT_ON_RMDIR is for synchronizing rmdir
+        * and subsystem's reference count handling. Please see css_get/put
+        * and css_tryget() and cgroup_wakeup_rmdir_waiter() implementation.
+        */
+       set_bit(CGRP_WAIT_ON_RMDIR, &cgrp->flags);
+
        /*
         * Call pre_destroy handlers of subsys. Notify subsystems
         * that rmdir() request comes.
         */
        ret = cgroup_call_pre_destroy(cgrp);
-       if (ret)
+       if (ret) {
+               clear_bit(CGRP_WAIT_ON_RMDIR, &cgrp->flags);
                return ret;
+       }
 
        mutex_lock(&cgroup_mutex);
        parent = cgrp->parent;
        if (atomic_read(&cgrp->count) || !list_empty(&cgrp->children)) {
+               clear_bit(CGRP_WAIT_ON_RMDIR, &cgrp->flags);
                mutex_unlock(&cgroup_mutex);
                return -EBUSY;
        }
-       /*
-        * css_put/get is provided for subsys to grab refcnt to css. In typical
-        * case, subsystem has no reference after pre_destroy(). But, under
-        * hierarchy management, some *temporal* refcnt can be hold.
-        * To avoid returning -EBUSY to a user, waitqueue is used. If subsys
-        * is really busy, it should return -EBUSY at pre_destroy(). wake_up
-        * is called when css_put() is called and refcnt goes down to 0.
-        */
-       set_bit(CGRP_WAIT_ON_RMDIR, &cgrp->flags);
        prepare_to_wait(&cgroup_rmdir_waitq, &wait, TASK_INTERRUPTIBLE);
-
        if (!cgroup_clear_css_refs(cgrp)) {
                mutex_unlock(&cgroup_mutex);
-               schedule();
+               /*
+                * Because someone may call cgroup_wakeup_rmdir_waiter() before
+                * prepare_to_wait(), we need to check this flag.
+                */
+               if (test_bit(CGRP_WAIT_ON_RMDIR, &cgrp->flags))
+                       schedule();
                finish_wait(&cgroup_rmdir_waitq, &wait);
                clear_bit(CGRP_WAIT_ON_RMDIR, &cgrp->flags);
                if (signal_pending(current))
@@ -3342,7 +3364,7 @@ void __css_put(struct cgroup_subsys_state *css)
                        set_bit(CGRP_RELEASABLE, &cgrp->flags);
                        check_for_release(cgrp);
                }
-               cgroup_wakeup_rmdir_waiters(cgrp);
+               cgroup_wakeup_rmdir_waiter(cgrp);
        }
        rcu_read_unlock();
 }