1 files changed, 107 insertions, 147 deletions

diff --git a/fs/fs-writeback.c b/fs/fs-writeback.c
index 1d1088f..0609607 100644
--- a/fs/fs-writeback.c
+++ b/fs/fs-writeback.c
@@ -63,24 +63,16 @@ struct bdi_work {
 };
 
 enum {
-	WS_USED_B = 0,
-	WS_ONSTACK_B,
+	WS_INPROGRESS = 0,
+	WS_ONSTACK,
 };
 
-#define WS_USED (1 << WS_USED_B)
-#define WS_ONSTACK (1 << WS_ONSTACK_B)
-
-static inline bool bdi_work_on_stack(struct bdi_work *work)
-{
-	return test_bit(WS_ONSTACK_B, &work->state);
-}
-
 static inline void bdi_work_init(struct bdi_work *work,
 				 struct wb_writeback_args *args)
 {
 	INIT_RCU_HEAD(&work->rcu_head);
 	work->args = *args;
-	work->state = WS_USED;
+	__set_bit(WS_INPROGRESS, &work->state);
 }
 
 /**
@@ -95,43 +87,16 @@ int writeback_in_progress(struct backing_dev_info *bdi)
 	return !list_empty(&bdi->work_list);
 }
 
-static void bdi_work_clear(struct bdi_work *work)
-{
-	clear_bit(WS_USED_B, &work->state);
-	smp_mb__after_clear_bit();
-	/*
-	 * work can have disappeared at this point. bit waitq functions
-	 * should be able to tolerate this, provided bdi_sched_wait does
-	 * not dereference it's pointer argument.
-	*/
-	wake_up_bit(&work->state, WS_USED_B);
-}
-
 static void bdi_work_free(struct rcu_head *head)
 {
 	struct bdi_work *work = container_of(head, struct bdi_work, rcu_head);
 
-	if (!bdi_work_on_stack(work))
-		kfree(work);
-	else
-		bdi_work_clear(work);
-}
-
-static void wb_work_complete(struct bdi_work *work)
-{
-	const enum writeback_sync_modes sync_mode = work->args.sync_mode;
-	int onstack = bdi_work_on_stack(work);
+	clear_bit(WS_INPROGRESS, &work->state);
+	smp_mb__after_clear_bit();
+	wake_up_bit(&work->state, WS_INPROGRESS);
 
-	/*
-	 * For allocated work, we can clear the done/seen bit right here.
-	 * For on-stack work, we need to postpone both the clear and free
-	 * to after the RCU grace period, since the stack could be invalidated
-	 * as soon as bdi_work_clear() has done the wakeup.
-	 */
-	if (!onstack)
-		bdi_work_clear(work);
-	if (sync_mode == WB_SYNC_NONE || onstack)
-		call_rcu(&work->rcu_head, bdi_work_free);
+	if (!test_bit(WS_ONSTACK, &work->state))
+		kfree(work);
 }
 
 static void wb_clear_pending(struct bdi_writeback *wb, struct bdi_work *work)
@@ -147,7 +112,7 @@ static void wb_clear_pending(struct bdi_writeback *wb, struct bdi_work *work)
 		list_del_rcu(&work->list);
 		spin_unlock(&bdi->wb_lock);
 
-		wb_work_complete(work);
+		call_rcu(&work->rcu_head, bdi_work_free);
 	}
 }
 
@@ -185,9 +150,9 @@ static void bdi_queue_work(struct backing_dev_info *bdi, struct bdi_work *work)
  * Used for on-stack allocated work items. The caller needs to wait until
  * the wb threads have acked the work before it's safe to continue.
  */
-static void bdi_wait_on_work_clear(struct bdi_work *work)
+static void bdi_wait_on_work_done(struct bdi_work *work)
 {
-	wait_on_bit(&work->state, WS_USED_B, bdi_sched_wait,
+	wait_on_bit(&work->state, WS_INPROGRESS, bdi_sched_wait,
 		    TASK_UNINTERRUPTIBLE);
 }
 
@@ -213,37 +178,28 @@ static void bdi_alloc_queue_work(struct backing_dev_info *bdi,
 }
 
 /**
- * bdi_sync_writeback - start and wait for writeback
- * @bdi: the backing device to write from
+ * bdi_queue_work_onstack - start and wait for writeback
  * @sb: write inodes from this super_block
  *
  * Description:
- *   This does WB_SYNC_ALL data integrity writeback and waits for the
- *   IO to complete. Callers must hold the sb s_umount semaphore for
+ *   This function initiates writeback and waits for the operation to
+ *   complete. Callers must hold the sb s_umount semaphore for
  *   reading, to avoid having the super disappear before we are done.
  */
-static void bdi_sync_writeback(struct backing_dev_info *bdi,
-			       struct super_block *sb)
+static void bdi_queue_work_onstack(struct wb_writeback_args *args)
 {
-	struct wb_writeback_args args = {
-		.sb		= sb,
-		.sync_mode	= WB_SYNC_ALL,
-		.nr_pages	= LONG_MAX,
-		.range_cyclic	= 0,
-	};
 	struct bdi_work work;
 
-	bdi_work_init(&work, &args);
-	work.state |= WS_ONSTACK;
+	bdi_work_init(&work, args);
+	__set_bit(WS_ONSTACK, &work.state);
 
-	bdi_queue_work(bdi, &work);
-	bdi_wait_on_work_clear(&work);
+	bdi_queue_work(args->sb->s_bdi, &work);
+	bdi_wait_on_work_done(&work);
 }
 
 /**
  * bdi_start_writeback - start writeback
  * @bdi: the backing device to write from
- * @sb: write inodes from this super_block
  * @nr_pages: the number of pages to write
  *
  * Description:
@@ -252,25 +208,34 @@ static void bdi_sync_writeback(struct backing_dev_info *bdi,
  *   completion. Caller need not hold sb s_umount semaphore.
  *
  */
-void bdi_start_writeback(struct backing_dev_info *bdi, struct super_block *sb,
-			 long nr_pages)
+void bdi_start_writeback(struct backing_dev_info *bdi, long nr_pages)
 {
 	struct wb_writeback_args args = {
-		.sb		= sb,
 		.sync_mode	= WB_SYNC_NONE,
 		.nr_pages	= nr_pages,
 		.range_cyclic	= 1,
 	};
 
-	/*
-	 * We treat @nr_pages=0 as the special case to do background writeback,
-	 * ie. to sync pages until the background dirty threshold is reached.
-	 */
-	if (!nr_pages) {
-		args.nr_pages = LONG_MAX;
-		args.for_background = 1;
-	}
+	bdi_alloc_queue_work(bdi, &args);
+}
 
+/**
+ * bdi_start_background_writeback - start background writeback
+ * @bdi: the backing device to write from
+ *
+ * Description:
+ *   This does WB_SYNC_NONE background writeback. The IO is only
+ *   started when this function returns, we make no guarentees on
+ *   completion. Caller need not hold sb s_umount semaphore.
+ */
+void bdi_start_background_writeback(struct backing_dev_info *bdi)
+{
+	struct wb_writeback_args args = {
+		.sync_mode	= WB_SYNC_NONE,
+		.nr_pages	= LONG_MAX,
+		.for_background = 1,
+		.range_cyclic	= 1,
+	};
 	bdi_alloc_queue_work(bdi, &args);
 }
 
@@ -561,48 +526,30 @@ select_queue:
 	return ret;
 }
 
-static void unpin_sb_for_writeback(struct super_block *sb)
-{
-	up_read(&sb->s_umount);
-	put_super(sb);
-}
-
-enum sb_pin_state {
-	SB_PINNED,
-	SB_NOT_PINNED,
-	SB_PIN_FAILED
-};
-
 /*
- * For WB_SYNC_NONE writeback, the caller does not have the sb pinned
+ * For background writeback the caller does not have the sb pinned
  * before calling writeback. So make sure that we do pin it, so it doesn't
  * go away while we are writing inodes from it.
  */
-static enum sb_pin_state pin_sb_for_writeback(struct writeback_control *wbc,
-					      struct super_block *sb)
+static bool pin_sb_for_writeback(struct super_block *sb)
 {
-	/*
-	 * Caller must already hold the ref for this
-	 */
-	if (wbc->sync_mode == WB_SYNC_ALL) {
-		WARN_ON(!rwsem_is_locked(&sb->s_umount));
-		return SB_NOT_PINNED;
-	}
 	spin_lock(&sb_lock);
+	if (list_empty(&sb->s_instances)) {
+		spin_unlock(&sb_lock);
+		return false;
+	}
+
 	sb->s_count++;
+	spin_unlock(&sb_lock);
+
 	if (down_read_trylock(&sb->s_umount)) {
-		if (sb->s_root) {
-			spin_unlock(&sb_lock);
-			return SB_PINNED;
-		}
-		/*
-		 * umounted, drop rwsem again and fall through to failure
-		 */
+		if (sb->s_root)
+			return true;
 		up_read(&sb->s_umount);
 	}
-	sb->s_count--;
-	spin_unlock(&sb_lock);
-	return SB_PIN_FAILED;
+
+	put_super(sb);
+	return false;
 }
 
 /*
@@ -681,24 +628,31 @@ static void writeback_inodes_wb(struct bdi_writeback *wb,
 		struct inode *inode = list_entry(wb->b_io.prev,
 						 struct inode, i_list);
 		struct super_block *sb = inode->i_sb;
-		enum sb_pin_state state;
 
-		if (wbc->sb && sb != wbc->sb) {
-			/* super block given and doesn't
-			   match, skip this inode */
-			redirty_tail(inode);
-			continue;
-		}
-		state = pin_sb_for_writeback(wbc, sb);
+		if (wbc->sb) {
+			/*
+			 * We are requested to write out inodes for a specific
+			 * superblock.  This means we already have s_umount
+			 * taken by the caller which also waits for us to
+			 * complete the writeout.
+			 */
+			if (sb != wbc->sb) {
+				redirty_tail(inode);
+				continue;
+			}
 
-		if (state == SB_PIN_FAILED) {
-			requeue_io(inode);
-			continue;
+			WARN_ON(!rwsem_is_locked(&sb->s_umount));
+
+			ret = writeback_sb_inodes(sb, wb, wbc);
+		} else {
+			if (!pin_sb_for_writeback(sb)) {
+				requeue_io(inode);
+				continue;
+			}
+			ret = writeback_sb_inodes(sb, wb, wbc);
+			drop_super(sb);
 		}
-		ret = writeback_sb_inodes(sb, wb, wbc);
 
-		if (state == SB_PINNED)
-			unpin_sb_for_writeback(sb);
 		if (ret)
 			break;
 	}
@@ -911,7 +865,7 @@ long wb_do_writeback(struct bdi_writeback *wb, int force_wait)
 		 * If this isn't a data integrity operation, just notify
 		 * that we have seen this work and we are now starting it.
 		 */
-		if (args.sync_mode == WB_SYNC_NONE)
+		if (!test_bit(WS_ONSTACK, &work->state))
 			wb_clear_pending(wb, work);
 
 		wrote += wb_writeback(wb, &args);
@@ -920,7 +874,7 @@ long wb_do_writeback(struct bdi_writeback *wb, int force_wait)
 		 * This is a data integrity writeback, so only do the
 		 * notification when we have completed the work.
 		 */
-		if (args.sync_mode == WB_SYNC_ALL)
+		if (test_bit(WS_ONSTACK, &work->state))
 			wb_clear_pending(wb, work);
 	}
 
@@ -978,42 +932,32 @@ int bdi_writeback_task(struct bdi_writeback *wb)
 }
 
 /*
- * Schedule writeback for all backing devices. This does WB_SYNC_NONE
- * writeback, for integrity writeback see bdi_sync_writeback().
+ * Start writeback of `nr_pages' pages.  If `nr_pages' is zero, write back
+ * the whole world.
  */
-static void bdi_writeback_all(struct super_block *sb, long nr_pages)
+void wakeup_flusher_threads(long nr_pages)
 {
+	struct backing_dev_info *bdi;
 	struct wb_writeback_args args = {
-		.sb		= sb,
-		.nr_pages	= nr_pages,
 		.sync_mode	= WB_SYNC_NONE,
 	};
-	struct backing_dev_info *bdi;
 
-	rcu_read_lock();
+	if (nr_pages) {
+		args.nr_pages = nr_pages;
+	} else {
+		args.nr_pages = global_page_state(NR_FILE_DIRTY) +
+				global_page_state(NR_UNSTABLE_NFS);
+	}
 
+	rcu_read_lock();
 	list_for_each_entry_rcu(bdi, &bdi_list, bdi_list) {
 		if (!bdi_has_dirty_io(bdi))
 			continue;
-
 		bdi_alloc_queue_work(bdi, &args);
 	}
-
 	rcu_read_unlock();
 }
 
-/*
- * Start writeback of `nr_pages' pages.  If `nr_pages' is zero, write back
- * the whole world.
- */
-void wakeup_flusher_threads(long nr_pages)
-{
-	if (nr_pages == 0)
-		nr_pages = global_page_state(NR_FILE_DIRTY) +
-				global_page_state(NR_UNSTABLE_NFS);
-	bdi_writeback_all(NULL, nr_pages);
-}
-
 static noinline void block_dump___mark_inode_dirty(struct inode *inode)
 {
 	if (inode->i_ino || strcmp(inode->i_sb->s_id, "bdev")) {
@@ -1218,12 +1162,17 @@ void writeback_inodes_sb(struct super_block *sb)
 {
 	unsigned long nr_dirty = global_page_state(NR_FILE_DIRTY);
 	unsigned long nr_unstable = global_page_state(NR_UNSTABLE_NFS);
-	long nr_to_write;
+	struct wb_writeback_args args = {
+		.sb		= sb,
+		.sync_mode	= WB_SYNC_NONE,
+	};
+
+	WARN_ON(!rwsem_is_locked(&sb->s_umount));
 
-	nr_to_write = nr_dirty + nr_unstable +
+	args.nr_pages = nr_dirty + nr_unstable +
 			(inodes_stat.nr_inodes - inodes_stat.nr_unused);
 
-	bdi_start_writeback(sb->s_bdi, sb, nr_to_write);
+	bdi_queue_work_onstack(&args);
 }
 EXPORT_SYMBOL(writeback_inodes_sb);
 
@@ -1237,7 +1186,9 @@ EXPORT_SYMBOL(writeback_inodes_sb);
 int writeback_inodes_sb_if_idle(struct super_block *sb)
 {
 	if (!writeback_in_progress(sb->s_bdi)) {
+		down_read(&sb->s_umount);
 		writeback_inodes_sb(sb);
+		up_read(&sb->s_umount);
 		return 1;
 	} else
 		return 0;
@@ -1253,7 +1204,16 @@ EXPORT_SYMBOL(writeback_inodes_sb_if_idle);
  */
 void sync_inodes_sb(struct super_block *sb)
 {
-	bdi_sync_writeback(sb->s_bdi, sb);
+	struct wb_writeback_args args = {
+		.sb		= sb,
+		.sync_mode	= WB_SYNC_ALL,
+		.nr_pages	= LONG_MAX,
+		.range_cyclic	= 0,
+	};
+
+	WARN_ON(!rwsem_is_locked(&sb->s_umount));
+
+	bdi_queue_work_onstack(&args);
 	wait_sb_inodes(sb);
 }
 EXPORT_SYMBOL(sync_inodes_sb);