Merge branch 'for-linus' of git://git.kernel.dk/linux-block

* 'for-linus' of git://git.kernel.dk/linux-block:
  floppy: use del_timer_sync() in init cleanup
  blk-cgroup: be able to remove the record of unplugged device
  block: Don't check QUEUE_FLAG_SAME_COMP in __blk_complete_request
  mm: Add comment explaining task state setting in bdi_forker_thread()
  mm: Cleanup clearing of BDI_pending bit in bdi_forker_thread()
  block: simplify force plug flush code a little bit
  block: change force plug flush call order
  block: Fix queue_flag update when rq_affinity goes from 2 to 1
  block: separate priority boosting from REQ_META
  block: remove READ_META and WRITE_META
  xen-blkback: fixed indentation and comments
  xen-blkback: Don't disconnect backend until state switched to XenbusStateClosed.

1 files changed, 21 insertions, 9 deletions

diff --git a/mm/backing-dev.c b/mm/backing-dev.c
index d6edf8d14f9c..a87da524a4a0 100644
--- a/mm/backing-dev.c
+++ b/mm/backing-dev.c
@@ -359,6 +359,17 @@ static unsigned long bdi_longest_inactive(void)
         return max(5UL * 60 * HZ, interval);
 }
 
+/*
+ * Clear pending bit and wakeup anybody waiting for flusher thread creation or
+ * shutdown
+ */
+static void bdi_clear_pending(struct backing_dev_info *bdi)
+{
+        clear_bit(BDI_pending, &bdi->state);
+        smp_mb__after_clear_bit();
+        wake_up_bit(&bdi->state, BDI_pending);
+}
+
 static int bdi_forker_thread(void *ptr)
 {
         struct bdi_writeback *me = ptr;
@@ -390,6 +401,13 @@ static int bdi_forker_thread(void *ptr)
                 }
 
                 spin_lock_bh(&bdi_lock);
+                /*
+                 * In the following loop we are going to check whether we have
+                 * some work to do without any synchronization with tasks
+                 * waking us up to do work for them. So we have to set task
+                 * state already here so that we don't miss wakeups coming
+                 * after we verify some condition.
+                 */
                 set_current_state(TASK_INTERRUPTIBLE);
 
                 list_for_each_entry(bdi, &bdi_list, bdi_list) {
@@ -469,11 +487,13 @@ static int bdi_forker_thread(void *ptr)
                                 spin_unlock_bh(&bdi->wb_lock);
                                 wake_up_process(task);
                         }
+                        bdi_clear_pending(bdi);
                         break;
 
                 case KILL_THREAD:
                         __set_current_state(TASK_RUNNING);
                         kthread_stop(task);
+                        bdi_clear_pending(bdi);
                         break;
 
                 case NO_ACTION:
@@ -489,16 +509,8 @@ static int bdi_forker_thread(void *ptr)
                         else
                                 schedule_timeout(msecs_to_jiffies(dirty_writeback_interval * 10));
                         try_to_freeze();
-                        /* Back to the main loop */
-                        continue;
+                        break;
                 }
-
-                /*
-                 * Clear pending bit and wakeup anybody waiting to tear us down.
-                 */
-                clear_bit(BDI_pending, &bdi->state);
-                smp_mb__after_clear_bit();
-                wake_up_bit(&bdi->state, BDI_pending);
         }
 
         return 0;