This patch adds tests for the return value of sb_getblk() in the ext2/3
filesystems.  In fs/buffer.c it is stated that the getblk() function never
fails.  However, it does can return NULL in some situations due to I/O
errors, which may lead us to NULL pointer dereferences
Signed-off-by: NGlauber de Oliveira Costa <glommer@br.ibm.com>
Signed-off-by: NAndrew Morton <akpm@osdl.org>
Signed-off-by: NLinus Torvalds <torvalds@osdl.org>