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block: disable block device DAX by default

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The recent *sync enabling discovered that we are inserting into the
block_device pagecache counter to the expectations of the dirty data
tracking for dax mappings.  This can lead to data corruption.

We want to support DAX for block devices eventually, but it requires
wider changes to properly manage the pagecache.

   dump_stack+0x85/0xc2
   dax_writeback_mapping_range+0x60/0xe0
   blkdev_writepages+0x3f/0x50
   do_writepages+0x21/0x30
   __filemap_fdatawrite_range+0xc6/0x100
   filemap_write_and_wait+0x4a/0xa0
   set_blocksize+0x70/0xd0
   sb_set_blocksize+0x1d/0x50
   ext4_fill_super+0x75b/0x3360
   mount_bdev+0x180/0x1b0
   ext4_mount+0x15/0x20
   mount_fs+0x38/0x170

Mark the support broken so its disabled by default, but otherwise still
available for testing.

Signed-off-by: Dan Williams <dan.j.williams@intel.com>
Signed-off-by: Ross Zwisler <ross.zwisler@linux.intel.com>
Reported-by: Ross Zwisler <ross.zwisler@linux.intel.com>
Suggested-by: Dave Chinner <david@fromorbit.com>
Reviewed-by: Jan Kara <jack@suse.cz>
Cc: Jens Axboe <axboe@fb.com>
Cc: Matthew Wilcox <matthew.r.wilcox@intel.com>
Cc: Al Viro <viro@ftp.linux.org.uk>
Cc: Theodore Ts'o <tytso@mit.edu>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Dan Williams 2016-02-26 15:19:43 -08:00 committed by Linus Torvalds
parent a4a8481ff6
commit 03cdadb040
2 changed files with 18 additions and 1 deletions
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13
block/Kconfig
View file

@ -88,6 +88,19 @@ config BLK_DEV_INTEGRITY
T10/SCSI Data Integrity Field or the T13/ATA External Path
Protection. If in doubt, say N.
config BLK_DEV_DAX
bool "Block device DAX support"
depends on FS_DAX
depends on BROKEN
help
When DAX support is available (CONFIG_FS_DAX) raw block
devices can also support direct userspace access to the
storage capacity via MMAP(2) similar to a file on a
DAX-enabled filesystem. However, the DAX I/O-path disables
some standard I/O-statistics, and the MMAP(2) path has some
operational differences due to bypassing the page
cache. If in doubt, say N.
config BLK_DEV_THROTTLING
bool "Block layer bio throttling support"
depends on BLK_CGROUP=y

6
fs/block_dev.c
View file

@ -1201,7 +1201,11 @@ static int __blkdev_get(struct block_device *bdev, fmode_t mode, int for_part)
bdev->bd_disk = disk;
bdev->bd_queue = disk->queue;
bdev->bd_contains = bdev;
bdev->bd_inode->i_flags = disk->fops->direct_access ? S_DAX : 0;
if (IS_ENABLED(CONFIG_BLK_DEV_DAX) && disk->fops->direct_access)
bdev->bd_inode->i_flags = S_DAX;
else
bdev->bd_inode->i_flags = 0;
if (!partno) {
ret = -ENXIO;
bdev->bd_part = disk_get_part(disk, partno);