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Commit 03cdadb0 authored by Dan Williams's avatar Dan Williams Committed by Linus Torvalds
Browse files

block: disable block device DAX by default 



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: default avatarDan Williams <dan.j.williams@intel.com>
Signed-off-by: default avatarRoss Zwisler <ross.zwisler@linux.intel.com>
Reported-by: default avatarRoss Zwisler <ross.zwisler@linux.intel.com>
Suggested-by: default avatarDave Chinner <david@fromorbit.com>
Reviewed-by: default avatarJan 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: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent a4a8481f

block/Kconfig

+13 −0
Original line number Diff line number Diff line
@@ -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

fs/block_dev.c

+5 −1
Original line number Diff line number Diff line
@@ -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);