On Tue, Apr 25, 2017 at 12:10:41PM +0200, Jan Kara wrote:
On Thu 20-04-17 21:44:36, Ross Zwisler wrote:
> dax_invalidate_mapping_entry() currently removes DAX exceptional entries
> only if they are clean and unlocked. This is done via:
> 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
> 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().
> Signed-off-by: Ross Zwisler <ross.zwisler(a)linux.intel.com>
> Fixes: c6dcf52c23d2 ("mm: Invalidate DAX radix tree entries only if
> Reported-by: Jan Kara <jack(a)suse.cz>
> Cc: <stable(a)vger.kernel.org> [4.10+]
Just as a side note - we wouldn't really have to unmap the mapping range
covered by the DAX exceptional entry. It would be enough to find out
whether such range is mapped and bail out in that case. But that would
still be pretty expensive for DAX - we'd have to do rmap walk similar as in
dax_mapping_entry_mkclean() and IMHO it is not worth it. So I agree with
what you did. You can add:
Reviewed-by: Jan Kara <jack(a)suse.cz>
Yep, that makes sense. Thanks for the review.