• Dan Williams's avatar
    filesystem-dax: Fix dax_layout_busy_page() livelock · d7782145
    Dan Williams authored
    In the presence of multi-order entries the typical
    pagevec_lookup_entries() pattern may loop forever:
    
    	while (index < end && pagevec_lookup_entries(&pvec, mapping, index,
    				min(end - index, (pgoff_t)PAGEVEC_SIZE),
    				indices)) {
    		...
    		for (i = 0; i < pagevec_count(&pvec); i++) {
    			index = indices[i];
    			...
    		}
    		index++; /* BUG */
    	}
    
    The loop updates 'index' for each index found and then increments to the
    next possible page to continue the lookup. However, if the last entry in
    the pagevec is multi-order then the next possible page index is more
    than 1 page away. Fix this locally for the filesystem-dax case by
    checking for dax-multi-order entries. Going forward new users of
    multi-order entries need to be similarly careful, or we need a generic
    way to report the page increment in the radix iterator.
    
    Fixes: 5fac7408 ("mm, fs, dax: handle layout changes to pinned dax...")
    Cc: <stable@vger.kernel.org>
    Cc: Ross Zwisler <zwisler@kernel.org>
    Cc: Matthew Wilcox <willy@infradead.org>
    Reviewed-by: default avatarJan Kara <jack@suse.cz>
    Signed-off-by: default avatarDan Williams <dan.j.williams@intel.com>
    d7782145
dax.c 49.4 KB