ext4: Take read lock during overwrite case.

When we are overwriting a file and not actually allocating new file system
blocks we need to take only the read lock on i_data_sem.

Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>

1 files changed, 24 insertions, 8 deletions

diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
index a7eb8bb4bdd4..89cd35386ff5 100644
--- a/fs/ext4/inode.c
+++ b/fs/ext4/inode.c
@@ -901,11 +901,31 @@ int ext4_get_blocks_wrap(handle_t *handle, struct inode *inode, sector_t block,
                         int create, int extend_disksize)
 {
         int retval;
-        if (create) {
-                down_write((&EXT4_I(inode)->i_data_sem));
+        /*
+         * Try to see if we can get  the block without requesting
+         * for new file system block.
+         */
+        down_read((&EXT4_I(inode)->i_data_sem));
+        if (EXT4_I(inode)->i_flags & EXT4_EXTENTS_FL) {
+                retval =  ext4_ext_get_blocks(handle, inode, block, max_blocks,
+                                bh, 0, 0);
         } else {
-                down_read((&EXT4_I(inode)->i_data_sem));
+                retval = ext4_get_blocks_handle(handle,
+                                inode, block, max_blocks, bh, 0, 0);
         }
+        up_read((&EXT4_I(inode)->i_data_sem));
+        if (!create || (retval > 0))
+                return retval;
+
+        /*
+         * We need to allocate new blocks which will result
+         * in i_data update
+         */
+        down_write((&EXT4_I(inode)->i_data_sem));
+        /*
+         * We need to check for EXT4 here because migrate
+         * could have changed the inode type in between
+         */
         if (EXT4_I(inode)->i_flags & EXT4_EXTENTS_FL) {
                 retval =  ext4_ext_get_blocks(handle, inode, block, max_blocks,
                                 bh, create, extend_disksize);
@@ -913,11 +933,7 @@ int ext4_get_blocks_wrap(handle_t *handle, struct inode *inode, sector_t block,
                 retval = ext4_get_blocks_handle(handle, inode, block,
                                 max_blocks, bh, create, extend_disksize);
         }
-        if (create) {
-                up_write((&EXT4_I(inode)->i_data_sem));
-        } else {
-                up_read((&EXT4_I(inode)->i_data_sem));
-        }
+        up_write((&EXT4_I(inode)->i_data_sem));
         return retval;
 }