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ext4: online defrag not supported with DAX 

Online defrag operations for ext4 are hard coded to use the page cache.
See ext4_ioctl() -> ext4_move_extents() -> move_extent_per_page()

When combined with DAX I/O, which circumvents the page cache, this can
result in data corruption.  This was observed with xfstests ext4/307 and
ext4/308.

Fix this by only allowing online defrag for non-DAX files.

Signed-off-by: Ross Zwisler <ross.zwisler@linux.intel.com>
Reviewed-by: Jan Kara <jack@suse.cz>
Cc: Theodore Ts'o <tytso@mit.edu>
Cc: Al Viro <viro@ftp.linux.org.uk>
Cc: Dan Williams <dan.j.williams@intel.com>
Cc: Dave Chinner <david@fromorbit.com>
Cc: Jens Axboe <axboe@fb.com>
Cc: Matthew Wilcox <matthew.r.wilcox@intel.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Ross Zwisler 2016-02-26 15:19:49 -08:00 committed by Linus Torvalds
parent 0a6cf9137d
commit 73f34a5e2c
1 changed files with 5 additions and 0 deletions
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5
fs/ext4/ioctl.c
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@ -583,6 +583,11 @@ long ext4_ioctl(struct file *filp, unsigned int cmd, unsigned long arg)
"Online defrag not supported with bigalloc");
err = -EOPNOTSUPP;
goto mext_out;
} else if (IS_DAX(inode)) {
ext4_msg(sb, KERN_ERR,
"Online defrag not supported with DAX");
err = -EOPNOTSUPP;
goto mext_out;
}
err = mnt_want_write_file(filp);