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 <dhowells@redhat.com>
Reviewed-by: Jeff Layton <jlayton@redhat.com>
Signed-off-by: Steve French <smfrench@gmail.com>

fs/cifs/file.c

@@ -3254,6 +3254,9 @@ static int cifs_readpages(struct file *file, struct address_space *mapping,
 	/*
 	 * 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);
@@ -3376,6 +3379,11 @@ static int cifs_readpages(struct file *file, struct address_space *mapping,
 		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

@@ -223,6 +223,13 @@ void __cifs_readpage_to_fscache(struct inode *inode, struct page *page)
 		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

@@ -54,6 +54,7 @@ extern int __cifs_readpages_from_fscache(struct inode *,
 					 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 *);
 
@@ -91,6 +92,13 @@ static inline void cifs_readpage_to_fscache(struct inode *inode,
 		__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 int cifs_fscache_register(void) { return 0; }
 static inline void cifs_fscache_unregister(void) {}
@@ -131,6 +139,11 @@ static inline int cifs_readpages_from_fscache(struct inode *inode,
 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 */
 
 #endif /* _CIFS_FSCACHE_H */