writeback: fix writeback_inodes_wb from writeback_inodes_sb

When we call writeback_inodes_wb from writeback_inodes_sb we always have
s_umount held, which currently makes the whole operation a no-op.

But if we are called to write out inodes for a specific superblock we always
have s_umount held, so replace the incorrect logic checking for WB_SYNC_ALL
which only worked by coincidence with the proper check for an explicit
superblock argument.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Jens Axboe <jaxboe@fusionio.com>

1 files changed, 23 insertions, 38 deletions

diff --git a/fs/fs-writeback.c b/fs/fs-writeback.c
index 2627f0dfcd9c..68ece4b18916 100644
--- a/fs/fs-writeback.c
+++ b/fs/fs-writeback.c
@@ -518,39 +518,19 @@ 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);
         sb->s_count++;
         if (down_read_trylock(&sb->s_umount)) {
                 if (sb->s_root) {
                         spin_unlock(&sb_lock);
-                        return SB_PINNED;
+                        return true;
                 }
                 /*
                  * umounted, drop rwsem again and fall through to failure
@@ -559,7 +539,7 @@ static enum sb_pin_state pin_sb_for_writeback(struct writeback_control *wbc,
         }
         sb->s_count--;
         spin_unlock(&sb_lock);
-        return SB_PIN_FAILED;
+        return false;
 }
 
 /*
@@ -638,24 +618,29 @@ 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))
+                                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;
         }