mm/readahead: Handle ractl nr_pages being modified

Filesystems are not currently permitted to modify the number of pages
in the ractl.  An upcoming patch to add readahead_expand() changes that
rule, so remove the check and resync the loop counter after every call
to the filesystem.

Tested-by: Jeff Layton <jlayton@kernel.org>
Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Signed-off-by: David Howells <dhowells@redhat.com>
Link: https://lore.kernel.org/r/20210420200116.3715790-1-willy@infradead.org/
Link: https://lore.kernel.org/r/20210421170923.4005574-1-willy@infradead.org/

diff --git a/mm/readahead.c b/mm/readahead.c
index 2088569a947e59c023f73ba94c8abecdbc080bd9..5b423ecc99f1be17327b9e6416f7d66de0402ecb 100644 (file)
--- a/mm/readahead.c
+++ b/mm/readahead.c
@@ -198,8 +198,6 @@ void page_cache_ra_unbounded(struct readahead_control *ractl,
        for (i = 0; i < nr_to_read; i++) {
                struct page *page = xa_load(&mapping->i_pages, index + i);
 
-               BUG_ON(index + i != ractl->_index + ractl->_nr_pages);
-
                if (page && !xa_is_value(page)) {
                        /*
                         * Page already present?  Kick off the current batch
@@ -210,6 +208,7 @@ void page_cache_ra_unbounded(struct readahead_control *ractl,
                         * not worth getting one just for that.
                         */
                        read_pages(ractl, &page_pool, true);
+                       i = ractl->_index + ractl->_nr_pages - index - 1;
                        continue;
                }
 
@@ -223,6 +222,7 @@ void page_cache_ra_unbounded(struct readahead_control *ractl,
                                        gfp_mask) < 0) {
                        put_page(page);
                        read_pages(ractl, &page_pool, true);
+                       i = ractl->_index + ractl->_nr_pages - index - 1;
                        continue;
                }
                if (i == nr_to_read - lookahead_size)