afs: Fix to take ref on page when PG_private is set

Fix afs to take a ref on a page when it sets PG_private on it and to drop
the ref when removing the flag.

Note that in afs_write_begin(), a lot of the time, PG_private is already
set on a page to which we're going to add some data.  In such a case, we
leave the bit set and mustn't increment the page count.

As suggested by Matthew Wilcox, use attach/detach_page_private() where
possible.

Fixes: 31143d5d515e ("AFS: implement basic file write support")
Reported-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Signed-off-by: David Howells <dhowells@redhat.com>
Reviewed-by: Matthew Wilcox (Oracle) <willy@infradead.org>

1 files changed, 4 insertions, 8 deletions

diff --git a/fs/afs/dir.c b/fs/afs/dir.c
index 1d2e61e0ab04..1bb5b9d7f0a2 100644
--- a/fs/afs/dir.c
+++ b/fs/afs/dir.c
@@ -281,8 +281,7 @@ retry:
 			if (ret < 0)
 				goto error;
 
-			set_page_private(req->pages[i], 1);
-			SetPagePrivate(req->pages[i]);
+			attach_page_private(req->pages[i], (void *)1);
 			unlock_page(req->pages[i]);
 			i++;
 		} else {
@@ -1975,8 +1974,7 @@ static int afs_dir_releasepage(struct page *page, gfp_t gfp_flags)
 
 	_enter("{{%llx:%llu}[%lu]}", dvnode->fid.vid, dvnode->fid.vnode, page->index);
 
-	set_page_private(page, 0);
-	ClearPagePrivate(page);
+	detach_page_private(page);
 
 	/* The directory will need reloading. */
 	if (test_and_clear_bit(AFS_VNODE_DIR_VALID, &dvnode->flags))
@@ -2003,8 +2001,6 @@ static void afs_dir_invalidatepage(struct page *page, unsigned int offset,
 		afs_stat_v(dvnode, n_inval);
 
 	/* we clean up only if the entire page is being invalidated */
-	if (offset == 0 && length == PAGE_SIZE) {
-		set_page_private(page, 0);
-		ClearPagePrivate(page);
-	}
+	if (offset == 0 && length == PAGE_SIZE)
+		detach_page_private(page);
 }