tree 9a5b63d45dc805383f7789bba75f7935626767fe
parent 825f1481ead4ce40671089bae7412ac3519e8caa
author Mingming Cao <cmm@us.ibm.com> 1203971395 -0500
committer Theodore Ts'o <tytso@mit.edu> 1203971395 -0500

ext4: Fix BUG when writing to an unitialized extent

This patch fixes a bug when writing to preallocated but uninitialized
blocks, which resulted in a BUG in fs/buffer.c saying that the buffer
is not mapped.

When writing to a file, ext4_get_block_wrap() is called with create=1 in
order to request that blocks be allocated if necessary.  It currently
calls ext4_get_blocks() with create=0 in order to do a lookup first.  If
the inode contains an unitialized data block, the buffer head is left
unampped, which ext4_get_blocks_wrap() returns, causing the BUG.

We fix this by checking to see if the buffer head is unmapped, and if
so, we make sure the the buffer head is mapped by calling
ext4_ext_get_blocks with create=1.

Signed-off-by: Mingming Cao <cmm@us.ibm.com>
Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>