[PATCH] add AOP_TRUNCATED_PAGE, prepend AOP_ to WRITEPAGE_ACTIVATE

readpage(), prepare_write(), and commit_write() callers are updated to
understand the special return code AOP_TRUNCATED_PAGE in the style of
writepage() and WRITEPAGE_ACTIVATE.  AOP_TRUNCATED_PAGE tells the caller that
the callee has unlocked the page and that the operation should be tried again
with a new page.  OCFS2 uses this to detect and work around a lock inversion in
its aop methods.  There should be no change in behaviour for methods that don't
return AOP_TRUNCATED_PAGE.

WRITEPAGE_ACTIVATE is also prepended with AOP_ for consistency and they are
made enums so that kerneldoc can be used to document their semantics.

Signed-off-by: Zach Brown <zach.brown@oracle.com>

1 files changed, 9 insertions, 6 deletions

diff --git a/mm/readahead.c b/mm/readahead.c
index 72e7adbb87c7..8d6eeaaa6296 100644
--- a/mm/readahead.c
+++ b/mm/readahead.c
@@ -158,7 +158,7 @@ static int read_pages(struct address_space *mapping, struct file *filp,
 {
         unsigned page_idx;
         struct pagevec lru_pvec;
-        int ret = 0;
+        int ret;
 
         if (mapping->a_ops->readpages) {
                 ret = mapping->a_ops->readpages(filp, mapping, pages, nr_pages);
@@ -171,14 +171,17 @@ static int read_pages(struct address_space *mapping, struct file *filp,
                 list_del(&page->lru);
                 if (!add_to_page_cache(page, mapping,
                                         page->index, GFP_KERNEL)) {
-                        mapping->a_ops->readpage(filp, page);
-                        if (!pagevec_add(&lru_pvec, page))
-                                __pagevec_lru_add(&lru_pvec);
-                } else {
-                        page_cache_release(page);
+                        ret = mapping->a_ops->readpage(filp, page);
+                        if (ret != AOP_TRUNCATED_PAGE) {
+                                if (!pagevec_add(&lru_pvec, page))
+                                        __pagevec_lru_add(&lru_pvec);
+                                continue;
+                        } /* else fall through to release */
                 }
+                page_cache_release(page);
         }
         pagevec_lru_add(&lru_pvec);
+        ret = 0;
 out:
         return ret;
 }