1 files changed, 22 insertions, 7 deletions

diff --git a/fs/fs-writeback.c b/fs/fs-writeback.c
index ef9bef118342..2d609a5fbfea 100644
--- a/fs/fs-writeback.c
+++ b/fs/fs-writeback.c
@@ -479,12 +479,28 @@ __writeback_single_inode(struct inode *inode, struct writeback_control *wbc)
          * write_inode()
          */
         spin_lock(&inode->i_lock);
-        /* Clear I_DIRTY_PAGES if we've written out all dirty pages */
-        if (!mapping_tagged(mapping, PAGECACHE_TAG_DIRTY))
-                inode->i_state &= ~I_DIRTY_PAGES;
+
         dirty = inode->i_state & I_DIRTY;
-        inode->i_state &= ~(I_DIRTY_SYNC | I_DIRTY_DATASYNC);
+        inode->i_state &= ~I_DIRTY;
+
+        /*
+         * Paired with smp_mb() in __mark_inode_dirty().  This allows
+         * __mark_inode_dirty() to test i_state without grabbing i_lock -
+         * either they see the I_DIRTY bits cleared or we see the dirtied
+         * inode.
+         *
+         * I_DIRTY_PAGES is always cleared together above even if @mapping
+         * still has dirty pages.  The flag is reinstated after smp_mb() if
+         * necessary.  This guarantees that either __mark_inode_dirty()
+         * sees clear I_DIRTY_PAGES or we see PAGECACHE_TAG_DIRTY.
+         */
+        smp_mb();
+
+        if (mapping_tagged(mapping, PAGECACHE_TAG_DIRTY))
+                inode->i_state |= I_DIRTY_PAGES;
+
         spin_unlock(&inode->i_lock);
+
         /* Don't write the inode if only I_DIRTY_PAGES was set */
         if (dirty & (I_DIRTY_SYNC | I_DIRTY_DATASYNC)) {
                 int err = write_inode(inode, wbc);
@@ -1148,12 +1164,11 @@ void __mark_inode_dirty(struct inode *inode, int flags)
         }
 
         /*
-         * make sure that changes are seen by all cpus before we test i_state
-         * -- mikulas
+         * Paired with smp_mb() in __writeback_single_inode() for the
+         * following lockless i_state test.  See there for details.
          */
         smp_mb();
 
-        /* avoid the locking if we can */
         if ((inode->i_state & flags) == flags)
                 return;