ext4: Properly initialize the buffer_head state

These struct buffer_heads are allocated on the stack (and hence are
initialized with stack garbage).  They are only used to call a
get_blocks() function, so that's mostly OK, but b_state must be
initialized to be 0 so we don't have any unexpected BH_* flags set by
accident, such as BH_Unwritten or BH_Delay.

Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>
Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>

3 files changed, 19 insertions, 3 deletions

diff --git a/fs/ext4/extents.c b/fs/ext4/extents.c
index e3a55eb8b26a..a953214f2829 100644
--- a/fs/ext4/extents.c
+++ b/fs/ext4/extents.c
@@ -3150,6 +3150,7 @@ retry:
                         ret = PTR_ERR(handle);
                         break;
                 }
+                map_bh.b_state = 0;
                 ret = ext4_get_blocks_wrap(handle, inode, block,
                                           max_blocks, &map_bh,
                                           EXT4_CREATE_UNINITIALIZED_EXT, 0, 0);
diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
index 2a9ffd528dd1..d7ad0bb73cd5 100644
--- a/fs/ext4/inode.c
+++ b/fs/ext4/inode.c
@@ -2055,7 +2055,20 @@ static int mpage_da_map_blocks(struct mpage_da_data *mpd)
         if ((mpd->b_state  & (1 << BH_Mapped)) &&
             !(mpd->b_state & (1 << BH_Delay)))
                 return 0;
-        new.b_state = mpd->b_state;
+        /*
+         * We need to make sure the BH_Delay flag is passed down to
+         * ext4_da_get_block_write(), since it calls
+         * ext4_get_blocks_wrap() with the EXT4_DELALLOC_RSVED flag.
+         * This flag causes ext4_get_blocks_wrap() to call
+         * ext4_da_update_reserve_space() if the passed buffer head
+         * has the BH_Delay flag set.  In the future, once we clean up
+         * the interfaces to ext4_get_blocks_wrap(), we should pass in
+         * a separate flag which requests that the delayed allocation
+         * statistics should be updated, instead of depending on the
+         * state information getting passed down via the map_bh's
+         * state bitmasks plus the magic EXT4_DELALLOC_RSVED flag.
+         */
+        new.b_state = mpd->b_state & (1 << BH_Delay);
         new.b_blocknr = 0;
         new.b_size = mpd->b_size;
         next = mpd->b_blocknr;
diff --git a/fs/mpage.c b/fs/mpage.c
index 680ba60863ff..42381bd6543b 100644
--- a/fs/mpage.c
+++ b/fs/mpage.c
@@ -379,7 +379,8 @@ mpage_readpages(struct address_space *mapping, struct list_head *pages,
         struct buffer_head map_bh;
         unsigned long first_logical_block = 0;
 
-        clear_buffer_mapped(&map_bh);
+        map_bh.b_state = 0;
+        map_bh.b_size = 0;
         for (page_idx = 0; page_idx < nr_pages; page_idx++) {
                 struct page *page = list_entry(pages->prev, struct page, lru);
 
@@ -412,7 +413,8 @@ int mpage_readpage(struct page *page, get_block_t get_block)
         struct buffer_head map_bh;
         unsigned long first_logical_block = 0;
 
-        clear_buffer_mapped(&map_bh);
+        map_bh.b_state = 0;
+        map_bh.b_size = 0;
         bio = do_mpage_readpage(bio, page, 1, &last_block_in_bio,
                         &map_bh, &first_logical_block, get_block);
         if (bio)