[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>

2 files changed, 20 insertions, 7 deletions

diff --git a/drivers/block/loop.c b/drivers/block/loop.c
index 96c664af8d06..a452b13620a2 100644
--- a/drivers/block/loop.c
+++ b/drivers/block/loop.c
@@ -213,7 +213,7 @@ static int do_lo_send_aops(struct loop_device *lo, struct bio_vec *bvec,
         struct address_space_operations *aops = mapping->a_ops;
         pgoff_t index;
         unsigned offset, bv_offs;
-        int len, ret = 0;
+        int len, ret;
 
         down(&mapping->host->i_sem);
         index = pos >> PAGE_CACHE_SHIFT;
@@ -232,9 +232,15 @@ static int do_lo_send_aops(struct loop_device *lo, struct bio_vec *bvec,
                 page = grab_cache_page(mapping, index);
                 if (unlikely(!page))
                         goto fail;
-                if (unlikely(aops->prepare_write(file, page, offset,
-                                offset + size)))
+                ret = aops->prepare_write(file, page, offset,
+                                          offset + size);
+                if (unlikely(ret)) {
+                        if (ret == AOP_TRUNCATED_PAGE) {
+                                page_cache_release(page);
+                                continue;
+                        }
                         goto unlock;
+                }
                 transfer_result = lo_do_transfer(lo, WRITE, page, offset,
                                 bvec->bv_page, bv_offs, size, IV);
                 if (unlikely(transfer_result)) {
@@ -251,9 +257,15 @@ static int do_lo_send_aops(struct loop_device *lo, struct bio_vec *bvec,
                         kunmap_atomic(kaddr, KM_USER0);
                 }
                 flush_dcache_page(page);
-                if (unlikely(aops->commit_write(file, page, offset,
-                                offset + size)))
+                ret = aops->commit_write(file, page, offset,
+                                         offset + size);
+                if (unlikely(ret)) {
+                        if (ret == AOP_TRUNCATED_PAGE) {
+                                page_cache_release(page);
+                                continue;
+                        }
                         goto unlock;
+                }
                 if (unlikely(transfer_result))
                         goto unlock;
                 bv_offs += size;
@@ -264,6 +276,7 @@ static int do_lo_send_aops(struct loop_device *lo, struct bio_vec *bvec,
                 unlock_page(page);
                 page_cache_release(page);
         }
+        ret = 0;
 out:
         up(&mapping->host->i_sem);
         return ret;
diff --git a/drivers/block/rd.c b/drivers/block/rd.c
index 68c60a5bcdab..ffd6abd6d5a0 100644
--- a/drivers/block/rd.c
+++ b/drivers/block/rd.c
@@ -154,7 +154,7 @@ static int ramdisk_commit_write(struct file *file, struct page *page,
 
 /*
  * ->writepage to the the blockdev's mapping has to redirty the page so that the
- * VM doesn't go and steal it.  We return WRITEPAGE_ACTIVATE so that the VM
+ * VM doesn't go and steal it.  We return AOP_WRITEPAGE_ACTIVATE so that the VM
  * won't try to (pointlessly) write the page again for a while.
  *
  * Really, these pages should not be on the LRU at all.
@@ -165,7 +165,7 @@ static int ramdisk_writepage(struct page *page, struct writeback_control *wbc)
                 make_page_uptodate(page);
         SetPageDirty(page);
         if (wbc->for_reclaim)
-                return WRITEPAGE_ACTIVATE;
+                return AOP_WRITEPAGE_ACTIVATE;
         unlock_page(page);
         return 0;
 }