fs/dax.c: fix inefficiency in dax_writeback_mapping_range()

commit 1eb643d02b21412e603b42cdd96010a2ac31c05f upstream.

dax_writeback_mapping_range() fails to update iteration index when
searching radix tree for entries needing cache flushing.  Thus each
pagevec worth of entries is searched starting from the start which is
inefficient and prone to livelocks.  Update index properly.

Link: http://lkml.kernel.org/r/20170619124531.21491-1-jack@suse.cz
Fixes: 9973c98ecfda3 ("dax: add support for fsync/sync")
Signed-off-by: Jan Kara <jack@suse.cz>
Reviewed-by: Ross Zwisler <ross.zwisler@linux.intel.com>
Cc: Dan Williams <dan.j.williams@intel.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/fs/dax.c b/fs/dax.c
index 285f4ab6f4986b230d986cba19a2686f8a1e2044..08a793c6158095bd65ce9cad2b2e85df89cca016 100644 (file)
--- a/fs/dax.c
+++ b/fs/dax.c
@@ -875,6 +875,7 @@ int dax_writeback_mapping_range(struct address_space *mapping,
                        if (ret < 0)
                                return ret;
                }
+               start_index = indices[pvec.nr - 1] + 1;
        }
        return 0;
 }