• Ross Zwisler's avatar
    dax: prevent invalidation of mapped DAX entries · 4636e70b
    Ross Zwisler authored
    Patch series "mm,dax: Fix data corruption due to mmap inconsistency",
    v4.
    
    This series fixes data corruption that can happen for DAX mounts when
    page faults race with write(2) and as a result page tables get out of
    sync with block mappings in the filesystem and thus data seen through
    mmap is different from data seen through read(2).
    
    The series passes testing with t_mmap_stale test program from Ross and
    also other mmap related tests on DAX filesystem.
    
    This patch (of 4):
    
    dax_invalidate_mapping_entry() currently removes DAX exceptional entries
    only if they are clean and unlocked.  This is done via:
    
      invalidate_mapping_pages()
        invalidate_exceptional_entry()
          dax_invalidate_mapping_entry()
    
    However, for page cache pages removed in invalidate_mapping_pages()
    there is an additional criteria which is that the page must not be
    mapped.  This is noted in the comments above invalidate_mapping_pages()
    and is checked in invalidate_inode_page().
    
    For DAX entries this means that we can can end up in a situation where a
    DAX exceptional entry, either a huge zero page or a regular DAX entry,
    could end up mapped but without an associated radix tree entry.  This is
    inconsistent with the rest of the DAX code and with what happens in the
    page cache case.
    
    We aren't able to unmap the DAX exceptional entry because according to
    its comments invalidate_mapping_pages() isn't allowed to block, and
    unmap_mapping_range() takes a write lock on the mapping->i_mmap_rwsem.
    
    Since we essentially never have unmapped DAX entries to evict from the
    radix tree, just remove dax_invalidate_mapping_entry().
    
    Fixes: c6dcf52c ("mm: Invalidate DAX radix tree entries only if appropriate")
    Link: http://lkml.kernel.org/r/20170510085419.27601-2-jack@suse.czSigned-off-by: default avatarRoss Zwisler <ross.zwisler@linux.intel.com>
    Signed-off-by: default avatarJan Kara <jack@suse.cz>
    Reported-by: default avatarJan Kara <jack@suse.cz>
    Cc: Dan Williams <dan.j.williams@intel.com>
    Cc: <stable@vger.kernel.org>    [4.10+]
    Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
    Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
    4636e70b
dax.c 40.6 KB