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

David Howells
2021-10-18T15:04:51Z

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@redhat.com>
---

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);
}