linux-kernel - [PATCH 51/67] fscache: Make fscache_write_to

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Message-ID: <163456942676.2614702.13709221260564510952.stgit@warthog.procyon.org.uk>
Date:   Mon, 18 Oct 2021 16:03:46 +0100
From:   David Howells <dhowells@...hat.com>
To:     linux-cachefs@...hat.com
Cc:     dhowells@...hat.com, Trond Myklebust <trondmy@...merspace.com>,
        Anna Schumaker <anna.schumaker@...app.com>,
        Steve French <sfrench@...ba.org>,
        Dominique Martinet <asmadeus@...ewreck.org>,
        Jeff Layton <jlayton@...hat.com>,
        Matthew Wilcox <willy@...radead.org>,
        Alexander Viro <viro@...iv.linux.org.uk>,
        Omar Sandoval <osandov@...ndov.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        linux-afs@...ts.infradead.org, linux-nfs@...r.kernel.org,
        linux-cifs@...r.kernel.org, ceph-devel@...r.kernel.org,
        v9fs-developer@...ts.sourceforge.net,
        linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: [PATCH 51/67] fscache: Make fscache_write_to_cache() conditional on
 cookie

Make fscache_write_to_cache() 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 - linkage will fail if CONFIG_FSCACHE is less than
CONFIG_AFS.  Analogous problems can affect other filesystems, e.g. 9p.

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

 (1) If cookie optimises down to constant NULL, term_func is called
     directly and may be inlined and the slow path is never called.

 (2) __fscache_write_to_cache() isn't called if cookie is dynamically NULL
     - and so, in such a case, term_func is called immediately.

Signed-off-by: David Howells <dhowells@...hat.com>
---

 include/linux/fscache.h |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/include/linux/fscache.h b/include/linux/fscache.h
index 847c076d05a6..ba192567d099 100644
--- a/include/linux/fscache.h
+++ b/include/linux/fscache.h
@@ -593,7 +593,7 @@ static inline void fscache_write_to_cache(struct fscache_cookie *cookie,
 					  netfs_io_terminated_t term_func,
 					  void *term_func_priv)
 {
-	if (fscache_available()) {
+	if (fscache_cookie_valid(cookie)) {
 		__fscache_write_to_cache(cookie, mapping, start, len, i_size,
 					 term_func, term_func_priv);
 	} else {