[Devel] [PATCH][RFC] incorrect direct io error handling (v3)

[Dmitriy Monakhov]

incorrect direct io error handling (v3)
Changes from v2:
 - Remove BUG_ON(!mutex_is_locked(..)) for non blkdev.
 - vmtruncate() called from generic_file_aio_write().
 - depends on patch titled:
   [PATH][RFC] mm: Move common segments checks to separate function

LOG:
If generic_file_direct_write() has fail (ENOSPC condition) inside 
__generic_file_aio_write_nolock() it may have instantiated
a few blocks outside i_size. And fsck will complain about wrong i_size
(ext2, ext3 and reiserfs interpret i_size and biggest block difference as error),
after fsck will fix error i_size will be increased to the biggest block,
but this blocks contain gurbage from previous write attempt, this is not 
information leak, but its silence file data corruption. This issue affect 
fs regardless the values of blocksize or pagesize.
We need truncate any block beyond i_size after write have failed , do in simular
generic_file_buffered_write() error path. Initialy i've proposed do it in
__generic_file_aio_write_nolock() with explicit guarantee i_mutex always held,
but not everybody was agree with it. So we may safely call vmtruncate() inside 
generic_file_aio_write(), here i_mutex already locked.
 
TEST_CASE:
open("/mnt/test/BIG_FILE", O_WRONLY|O_CREAT|O_DIRECT, 0666) = 3
write(3, "aaaaaaaaaaaaaaa"..., 104857600) = -1 ENOSPC (No space left on device)

#stat /mnt/test/BIG_FILE
  File: `/mnt/test/BIG_FILE'
  Size: 0               Blocks: 110896     IO Block: 1024   regular empty file
<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<^^^^^^^^file size is less than biggest block idx

Device: fe07h/65031d    Inode: 14          Links: 1
Access: (0644/-rw-r--r--)  Uid: (    0/    root)   Gid: (    0/    root)
Access: 2007-01-24 20:03:38.000000000 +0300
Modify: 2007-01-24 20:03:38.000000000 +0300
Change: 2007-01-24 20:03:39.000000000 +0300

#fsck.ext3 -f /dev/VG/test 
e2fsck 1.39 (29-May-2006)
Pass 1: Checking inodes, blocks, and sizes
Inode 14, i_size is 0, should be 56556544.  Fix<y>? yes
Pass 2: Checking directory structure

Signed-off-by: Dmitriy Monakhov <dmonakhov at openvz.org>
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