Eric Sandeen e9e3bcecf4 ext4: serialize unaligned asynchronous DIO ... ext4 has a data corruption case when doing non-block-aligned asynchronous direct IO into a sparse file, as demonstrated by xfstest 240. The root cause is that while ext4 preallocates space in the hole, mappings of that space still look "new" and dio_zero_block() will zero out the unwritten portions. When more than one AIO thread is going, they both find this "new" block and race to zero out their portion; this is uncoordinated and causes data corruption. Dave Chinner fixed this for xfs by simply serializing all unaligned asynchronous direct IO. I've done the same here. The difference is that we only wait on conversions, not all IO. This is a very big hammer, and I'm not very pleased with stuffing this into ext4_file_write(). But since ext4 is DIO_LOCKING, we need to serialize it at this high level. I tried to move this into ext4_ext_direct_IO, but by then we have the i_mutex already, and we will wait on the work queue to do conversions - which must also take the i_mutex. So that won't work. This was originally exposed by qemu-kvm installing to a raw disk image with a normal sector-63 alignment. I've tested a backport of this patch with qemu, and it does avoid the corruption. It is also quite a lot slower (14 min for package installs, vs. 8 min for well-aligned) but I'll take slow correctness over fast corruption any day. Mingming suggested that we can track outstanding conversions, and wait on those so that non-sparse files won't be affected, and I've implemented that here; unaligned AIO to nonsparse files won't take a perf hit. [tytso@mit.edu: Keep the mutex as a hashed array instead of bloating the ext4 inode] [tytso@mit.edu: Fix up namespace issues so that global variables are protected with an "ext4_" prefix.] Signed-off-by: Eric Sandeen <sandeen@redhat.com> Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>		2011-02-12 08:17:34 -05:00
..
acl.c
acl.h
balloc.c
bitmap.c
block_validity.c
dir.c
ext4.h	ext4: serialize unaligned asynchronous DIO	2011-02-12 08:17:34 -05:00
ext4_extents.h
ext4_jbd2.c
ext4_jbd2.h
extents.c	ext4: serialize unaligned asynchronous DIO	2011-02-12 08:17:34 -05:00
file.c	ext4: serialize unaligned asynchronous DIO	2011-02-12 08:17:34 -05:00
fsync.c
hash.c
ialloc.c
inode.c
ioctl.c
Kconfig
Makefile
mballoc.c	ext4: make grpinfo slab cache names static	2011-02-12 08:12:18 -05:00
mballoc.h
migrate.c
move_extent.c
namei.c
page-io.c	ext4: serialize unaligned asynchronous DIO	2011-02-12 08:17:34 -05:00
resize.c
super.c	ext4: serialize unaligned asynchronous DIO	2011-02-12 08:17:34 -05:00
symlink.c
xattr.c
xattr.h
xattr_security.c
xattr_trusted.c
xattr_user.c