ext4: fix credits computing for indirect mapped files

When writing a contiguous set of blocks, two indirect blocks could be
needed depending on how the blocks are aligned, so we need to increase
the number of credits needed by one.

[ Also fixed a another bug which could further underestimate the
  number of journal credits needed by 1; the code was using integer
  division instead of DIV_ROUND_UP() -- tytso]

Signed-off-by: Yongqiang Yang <xiaoqiangnk@gmail.com>
Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>
Cc: stable@kernel.org

1 files changed, 5 insertions, 6 deletions

diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
index 1a86282b9024..7d11e02ad01d 100644
--- a/fs/ext4/inode.c
+++ b/fs/ext4/inode.c
@@ -5398,13 +5398,12 @@ static int ext4_indirect_trans_blocks(struct inode *inode, int nrblocks,
         /* if nrblocks are contiguous */
         if (chunk) {
                 /*
-                 * With N contiguous data blocks, it need at most
-                 * N/EXT4_ADDR_PER_BLOCK(inode->i_sb) indirect blocks
-                 * 2 dindirect blocks
-                 * 1 tindirect block
+                 * With N contiguous data blocks, we need at most
+                 * N/EXT4_ADDR_PER_BLOCK(inode->i_sb) + 1 indirect blocks,
+                 * 2 dindirect blocks, and 1 tindirect block
                  */
-                indirects = nrblocks / EXT4_ADDR_PER_BLOCK(inode->i_sb);
-                return indirects + 3;
+                return DIV_ROUND_UP(nrblocks,
+                                    EXT4_ADDR_PER_BLOCK(inode->i_sb)) + 4;
         }
         /*
          * if nrblocks are not contiguous, worse case, each block touch