mm-add-comment-explaining-task-state-setting-in-bdi_forker_thread-fix

[pandora-kernel.git] / mm / backing-dev.c

diff --git a/mm/backing-dev.c b/mm/backing-dev.c
index d6edf8d..7520ef0 100644 (file)
--- 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 +401,12 @@ 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. Set the task state here
+                * so that we don't miss wakeups after verifying conditions.
+                */
                set_current_state(TASK_INTERRUPTIBLE);
 
                list_for_each_entry(bdi, &bdi_list, bdi_list) {
@@ -469,11 +486,13 @@ 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 +508,8 @@ 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;