[PATCH 50/67] fscache: Make fscache_clear_page_bits() conditional on cookie

[David Howells]

Make fscache_clear_page_bits() conditional on cookie not being NULL, rather
than merely conditional on CONFIG_FSCACHE=[ym].  The problem with the
latter is if a filesystem, say afs, has CONFIG_AFS_FSCACHE=n but calls into
this function - in which it linkage will fail if CONFIG_FSCACHE is less
than CONFIG_AFS.  Analogous problems can affect other filesystems, e.g. 9p.

Making fscache_clear_page_bits() conditional on the cookie achieves two
things:

 (1) If cookie optimised down to constant NULL, the rest of the function is
     thrown away and the slow path is never called.

 (2) __fscache_clear_page_bits() isn't called if there's no cookie - and
     so, in such a case, the pages won't iterated over attempting to clear
     PG_fscache bits that haven't been set.

Signed-off-by: David Howells <dhowells@xxxxxxxxxx>
---

 fs/fscache/io.c         |    5 +++--
 include/linux/fscache.h |    8 +++++---
 2 files changed, 8 insertions(+), 5 deletions(-)

diff --git a/fs/fscache/io.c b/fs/fscache/io.c
index 3910cba65545..bc8d1ac0e85c 100644
--- a/fs/fscache/io.c
+++ b/fs/fscache/io.c
@@ -316,7 +316,8 @@ static void fscache_wreq_done(void *priv, ssize_t transferred_or_error,
 {
 	struct fscache_write_request *wreq = priv;
 
-	fscache_clear_page_bits(wreq->mapping, wreq->start, wreq->len);
+	fscache_clear_page_bits(fscache_cres_cookie(&wreq->cache_resources),
+				wreq->mapping, wreq->start, wreq->len);
 
 	if (wreq->term_func)
 		wreq->term_func(wreq->term_func_priv, transferred_or_error,
@@ -373,7 +374,7 @@ void __fscache_write_to_cache(struct fscache_cookie *cookie,
 abandon_free:
 	kfree(wreq);
 abandon:
-	fscache_clear_page_bits(mapping, start, len);
+	fscache_clear_page_bits(cookie, mapping, start, len);
 	if (term_func)
 		term_func(term_func_priv, ret, false);
 }
diff --git a/include/linux/fscache.h b/include/linux/fscache.h
index fe4d588641da..847c076d05a6 100644
--- a/include/linux/fscache.h
+++ b/include/linux/fscache.h
@@ -549,6 +549,7 @@ int fscache_write(struct netfs_cache_resources *cres,
 
 /**
  * fscache_clear_page_bits - Clear the PG_fscache bits from a set of pages
+ * @cookie: The cookie representing the cache object
  * @mapping: The netfs inode to use as the source
  * @start: The start position in @mapping
  * @len: The amount of data to unlock
@@ -556,10 +557,11 @@ int fscache_write(struct netfs_cache_resources *cres,
  * Clear the PG_fscache flag from a sequence of pages and wake up anyone who's
  * waiting.
  */
-static inline void fscache_clear_page_bits(struct address_space *mapping,
+static inline void fscache_clear_page_bits(struct fscache_cookie *cookie,
+					   struct address_space *mapping,
 					   loff_t start, size_t len)
 {
-	if (fscache_available())
+	if (fscache_cookie_valid(cookie))
 		__fscache_clear_page_bits(mapping, start, len);
 }
 
@@ -595,7 +597,7 @@ static inline void fscache_write_to_cache(struct fscache_cookie *cookie,
 		__fscache_write_to_cache(cookie, mapping, start, len, i_size,
 					 term_func, term_func_priv);
 	} else {
-		fscache_clear_page_bits(mapping, start, len);
+		fscache_clear_page_bits(cookie, mapping, start, len);
 		if (term_func)
 			term_func(term_func_priv, -ENOBUFS, false);
 	}