1 files changed, 51 insertions, 5 deletions

diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
index 7dd9b50d5ebc..945cbf6cb1fc 100644
--- a/fs/ext4/inode.c
+++ b/fs/ext4/inode.c
@@ -403,6 +403,7 @@ static ext4_fsblk_t ext4_find_near(struct inode *inode, Indirect *ind)
         __le32 *start = ind->bh ? (__le32*) ind->bh->b_data : ei->i_data;
         __le32 *p;
         ext4_fsblk_t bg_start;
+        ext4_fsblk_t last_block;
         ext4_grpblk_t colour;
 
         /* Try to find previous block */
@@ -420,8 +421,13 @@ static ext4_fsblk_t ext4_find_near(struct inode *inode, Indirect *ind)
          * into the same cylinder group then.
          */
         bg_start = ext4_group_first_block_no(inode->i_sb, ei->i_block_group);
-        colour = (current->pid % 16) *
+        last_block = ext4_blocks_count(EXT4_SB(inode->i_sb)->s_es) - 1;
+
+        if (bg_start + EXT4_BLOCKS_PER_GROUP(inode->i_sb) <= last_block)
+                colour = (current->pid % 16) *
                         (EXT4_BLOCKS_PER_GROUP(inode->i_sb) / 16);
+        else
+                colour = (current->pid % 16) * ((last_block - bg_start) / 16);
         return bg_start + colour;
 }
 
@@ -768,7 +774,6 @@ err_out:
  *
  * `handle' can be NULL if create == 0.
  *
- * The BKL may not be held on entry here.  Be sure to take it early.
  * return > 0, # of blocks mapped or allocated.
  * return = 0, if plain lookup failed.
  * return < 0, error case.
@@ -903,11 +908,38 @@ out:
  */
 #define DIO_CREDITS 25
 
+
+/*
+ *
+ *
+ * ext4_ext4 get_block() wrapper function
+ * It will do a look up first, and returns if the blocks already mapped.
+ * Otherwise it takes the write lock of the i_data_sem and allocate blocks
+ * and store the allocated blocks in the result buffer head and mark it
+ * mapped.
+ *
+ * If file type is extents based, it will call ext4_ext_get_blocks(),
+ * Otherwise, call with ext4_get_blocks_handle() to handle indirect mapping
+ * based files
+ *
+ * On success, it returns the number of blocks being mapped or allocate.
+ * if create==0 and the blocks are pre-allocated and uninitialized block,
+ * the result buffer head is unmapped. If the create ==1, it will make sure
+ * the buffer head is mapped.
+ *
+ * It returns 0 if plain look up failed (blocks have not been allocated), in
+ * that casem, buffer head is unmapped
+ *
+ * It returns the error in case of allocation failure.
+ */
 int ext4_get_blocks_wrap(handle_t *handle, struct inode *inode, sector_t block,
                         unsigned long max_blocks, struct buffer_head *bh,
                         int create, int extend_disksize)
 {
         int retval;
+
+        clear_buffer_mapped(bh);
+
         /*
          * Try to see if we can get  the block without requesting
          * for new file system block.
@@ -921,12 +953,26 @@ int ext4_get_blocks_wrap(handle_t *handle, struct inode *inode, sector_t block,
                                 inode, block, max_blocks, bh, 0, 0);
         }
         up_read((&EXT4_I(inode)->i_data_sem));
-        if (!create || (retval > 0))
+
+        /* If it is only a block(s) look up */
+        if (!create)
+                return retval;
+
+        /*
+         * Returns if the blocks have already allocated
+         *
+         * Note that if blocks have been preallocated
+         * ext4_ext_get_block() returns th create = 0
+         * with buffer head unmapped.
+         */
+        if (retval > 0 && buffer_mapped(bh))
                 return retval;
 
         /*
-         * We need to allocate new blocks which will result
-         * in i_data update
+         * New blocks allocate and/or writing to uninitialized extent
+         * will possibly result in updating i_data, so we take
+         * the write lock of i_data_sem, and call get_blocks()
+         * with create == 1 flag.
          */
         down_write((&EXT4_I(inode)->i_data_sem));
         /*