CIFS: FS-Cache: Uncache unread pages in cifs_readpages() before freeing them

In cifs_readpages(), we may decide we don't want to read a page after all -
but the page may already have passed through fscache_read_or_alloc_pages() and
thus have marks and reservations set. Thus we have to call
fscache_readpages_cancel() or fscache_uncache_page() on the pages we're
returning to clear the marks.

NFS, AFS and 9P should be unaffected by this as they call read_cache_pages()
which does the cleanup for you.

Signed-off-by: David Howells <[e-mail]>
Reviewed-by: Jeff Layton <[e-mail]>
Signed-off-by: Steve French <[e-mail]>

fs/cifs/file.c

···
 	/*
 	 * Reads as many pages as possible from fscache. Returns -ENOBUFS
 	 * immediately if the cookie is negative
+	 *
+	 * After this point, every page in the list might have PG_fscache set,
+	 * so we will need to clean that up off of every page we don't use.
 	 */
 	rc = cifs_readpages_from_fscache(mapping->host, mapping, page_list,
 					 &num_pages);
···
 		kref_put(&rdata->refcount, cifs_readdata_release);
 	}
 
+	/* Any pages that have been shown to fscache but didn't get added to
+	 * the pagecache must be uncached before they get returned to the
+	 * allocator.
+	 */
+	cifs_fscache_readpages_cancel(mapping->host, page_list);
 	return rc;
 }
 

fs/cifs/fscache.c

···
 		fscache_uncache_page(CIFS_I(inode)->fscache, page);
 }
 
+void __cifs_fscache_readpages_cancel(struct inode *inode, struct list_head *pages)
+{
+	cifs_dbg(FYI, "%s: (fsc: %p, i: %p)\n",
+		 __func__, CIFS_I(inode)->fscache, inode);
+	fscache_readpages_cancel(CIFS_I(inode)->fscache, pages);
+}
+
 void __cifs_fscache_invalidate_page(struct page *page, struct inode *inode)
 {
 	struct cifsInodeInfo *cifsi = CIFS_I(inode);

fs/cifs/fscache.h

···
 					 struct address_space *,
 					 struct list_head *,
 					 unsigned *);
+extern void __cifs_fscache_readpages_cancel(struct inode *, struct list_head *);
 
 extern void __cifs_readpage_to_fscache(struct inode *, struct page *);
 
···
 {
 	if (PageFsCache(page))
 		__cifs_readpage_to_fscache(inode, page);
+}
+
+static inline void cifs_fscache_readpages_cancel(struct inode *inode,
+						 struct list_head *pages)
+{
+	if (CIFS_I(inode)->fscache)
+		return __cifs_fscache_readpages_cancel(inode, pages);
 }
 
 #else /* CONFIG_CIFS_FSCACHE */
···
 
 static inline void cifs_readpage_to_fscache(struct inode *inode,
 			struct page *page) {}
+
+static inline void cifs_fscache_readpages_cancel(struct inode *inode,
+						 struct list_head *pages)
+{
+}
 
 #endif /* CONFIG_CIFS_FSCACHE */