Btrfs: Fix the unplug_io_fn to grab a consistent copy of page->mapping
Signed-off-by: Chris Mason <chris.mason@oracle.com>
diff --git a/fs/btrfs/disk-io.c b/fs/btrfs/disk-io.c
index 19c258d..1281c39 100644
--- a/fs/btrfs/disk-io.c
+++ b/fs/btrfs/disk-io.c
@@ -936,14 +936,25 @@
struct inode *inode;
struct extent_map_tree *em_tree;
struct extent_map *em;
+ struct address_space *mapping;
u64 offset;
+ /* the generic O_DIRECT read code does this */
if (!page) {
__unplug_io_fn(bdi, page);
return;
}
- inode = page->mapping->host;
+ /*
+ * page->mapping may change at any time. Get a consistent copy
+ * and use that for everything below
+ */
+ smp_mb();
+ mapping = page->mapping;
+ if (!mapping)
+ return;
+
+ inode = mapping->host;
offset = page_offset(page);
em_tree = &BTRFS_I(inode)->extent_tree;