1 files changed, 44 insertions, 4 deletions

diff --git a/fs/btrfs/extent_io.c b/fs/btrfs/extent_io.c
index 5e76a474cb7e..92ac5192c518 100644
--- a/fs/btrfs/extent_io.c
+++ b/fs/btrfs/extent_io.c
@@ -1946,6 +1946,7 @@ void set_page_extent_mapped(struct page *page)
 
 static void set_page_extent_head(struct page *page, unsigned long len)
 {
+        WARN_ON(!PagePrivate(page));
         set_page_private(page, EXTENT_PAGE_PRIVATE_FIRST_PAGE | len << 2);
 }
 
@@ -2821,9 +2822,17 @@ int try_release_extent_state(struct extent_map_tree *map,
                  * at this point we can safely clear everything except the
                  * locked bit and the nodatasum bit
                  */
-                clear_extent_bit(tree, start, end,
+                ret = clear_extent_bit(tree, start, end,
                                  ~(EXTENT_LOCKED | EXTENT_NODATASUM),
                                  0, 0, NULL, mask);
+
+                /* if clear_extent_bit failed for enomem reasons,
+                 * we can't allow the release to continue.
+                 */
+                if (ret < 0)
+                        ret = 0;
+                else
+                        ret = 1;
         }
         return ret;
 }
@@ -3194,7 +3203,13 @@ struct extent_buffer *alloc_extent_buffer(struct extent_io_tree *tree,
                 }
                 if (!PageUptodate(p))
                         uptodate = 0;
-                unlock_page(p);
+
+                /*
+                 * see below about how we avoid a nasty race with release page
+                 * and why we unlock later
+                 */
+                if (i != 0)
+                        unlock_page(p);
         }
         if (uptodate)
                 set_bit(EXTENT_BUFFER_UPTODATE, &eb->bflags);
@@ -3218,9 +3233,26 @@ struct extent_buffer *alloc_extent_buffer(struct extent_io_tree *tree,
         atomic_inc(&eb->refs);
         spin_unlock(&tree->buffer_lock);
         radix_tree_preload_end();
+
+        /*
+         * there is a race where release page may have
+         * tried to find this extent buffer in the radix
+         * but failed.  It will tell the VM it is safe to
+         * reclaim the, and it will clear the page private bit.
+         * We must make sure to set the page private bit properly
+         * after the extent buffer is in the radix tree so
+         * it doesn't get lost
+         */
+        set_page_extent_mapped(eb->first_page);
+        set_page_extent_head(eb->first_page, eb->len);
+        if (!page0)
+                unlock_page(eb->first_page);
         return eb;
 
 free_eb:
+        if (eb->first_page && !page0)
+                unlock_page(eb->first_page);
+
         if (!atomic_dec_and_test(&eb->refs))
                 return exists;
         btrfs_release_extent_buffer(eb);
@@ -3271,10 +3303,11 @@ int clear_extent_buffer_dirty(struct extent_io_tree *tree,
                         continue;
 
                 lock_page(page);
+                WARN_ON(!PagePrivate(page));
+
+                set_page_extent_mapped(page);
                 if (i == 0)
                         set_page_extent_head(page, eb->len);
-                else
-                        set_page_private(page, EXTENT_PAGE_PRIVATE);
 
                 clear_page_dirty_for_io(page);
                 spin_lock_irq(&page->mapping->tree_lock);
@@ -3464,6 +3497,13 @@ int read_extent_buffer_pages(struct extent_io_tree *tree,
 
         for (i = start_i; i < num_pages; i++) {
                 page = extent_buffer_page(eb, i);
+
+                WARN_ON(!PagePrivate(page));
+
+                set_page_extent_mapped(page);
+                if (i == 0)
+                        set_page_extent_head(page, eb->len);
+
                 if (inc_all_pages)
                         page_cache_get(page);
                 if (!PageUptodate(page)) {