fscache: Use refcount_t for the cookie refcount instead of atomic_t

Use refcount_t for the fscache_cookie refcount instead of atomic_t and
rename the 'usage' member to 'ref' in such cases.  The tracepoints that
reference it change from showing "u=%d" to "r=%d".

Signed-off-by: David Howells <dhowells@redhat.com>
Reviewed-by: Jeff Layton <jlayton@redhat.com>
cc: linux-cachefs@redhat.com
Link: https://lore.kernel.org/r/162431204358.2908479.8006938388213098079.stgit@warthog.procyon.org.uk/

1 files changed, 21 insertions, 10 deletions

diff --git a/fs/fscache/cookie.c b/fs/fscache/cookie.c
index 6df3732cf1b4..cd42be646ed3 100644
--- a/fs/fscache/cookie.c
+++ b/fs/fscache/cookie.c
@@ -164,7 +164,7 @@ struct fscache_cookie *fscache_alloc_cookie(
 			goto nomem;
 	}
 
-	atomic_set(&cookie->usage, 1);
+	refcount_set(&cookie->ref, 1);
 	atomic_set(&cookie->n_children, 0);
 	cookie->debug_id = atomic_inc_return(&fscache_cookie_debug_id);
 
@@ -225,7 +225,7 @@ struct fscache_cookie *fscache_hash_cookie(struct fscache_cookie *candidate)
 
 collision:
 	if (test_and_set_bit(FSCACHE_COOKIE_ACQUIRED, &cursor->flags)) {
-		trace_fscache_cookie(cursor->debug_id, atomic_read(&cursor->usage),
+		trace_fscache_cookie(cursor->debug_id, refcount_read(&cursor->ref),
 				     fscache_cookie_collision);
 		pr_err("Duplicate cookie detected\n");
 		fscache_print_cookie(cursor, 'O');
@@ -826,13 +826,12 @@ void __fscache_relinquish_cookie(struct fscache_cookie *cookie,
 	BUG_ON(!radix_tree_empty(&cookie->stores));
 
 	if (cookie->parent) {
-		ASSERTCMP(atomic_read(&cookie->parent->usage), >, 0);
+		ASSERTCMP(refcount_read(&cookie->parent->ref), >, 0);
 		ASSERTCMP(atomic_read(&cookie->parent->n_children), >, 0);
 		atomic_dec(&cookie->parent->n_children);
 	}
 
 	/* Dispose of the netfs's link to the cookie */
-	ASSERTCMP(atomic_read(&cookie->usage), >, 0);
 	fscache_cookie_put(cookie, fscache_cookie_put_relinquish);
 
 	_leave("");
@@ -862,18 +861,17 @@ void fscache_cookie_put(struct fscache_cookie *cookie,
 			enum fscache_cookie_trace where)
 {
 	struct fscache_cookie *parent;
-	int usage;
+	int ref;
 
 	_enter("%x", cookie->debug_id);
 
 	do {
 		unsigned int cookie_debug_id = cookie->debug_id;
-		usage = atomic_dec_return(&cookie->usage);
-		trace_fscache_cookie(cookie_debug_id, usage, where);
+		bool zero = __refcount_dec_and_test(&cookie->ref, &ref);
 
-		if (usage > 0)
+		trace_fscache_cookie(cookie_debug_id, ref - 1, where);
+		if (!zero)
 			return;
-		BUG_ON(usage < 0);
 
 		parent = cookie->parent;
 		fscache_unhash_cookie(cookie);
@@ -887,6 +885,19 @@ void fscache_cookie_put(struct fscache_cookie *cookie,
 }
 
 /*
+ * Get a reference to a cookie.
+ */
+struct fscache_cookie *fscache_cookie_get(struct fscache_cookie *cookie,
+					  enum fscache_cookie_trace where)
+{
+	int ref;
+
+	__refcount_inc(&cookie->ref, &ref);
+	trace_fscache_cookie(cookie->debug_id, ref + 1, where);
+	return cookie;
+}
+
+/*
  * check the consistency between the netfs inode and the backing cache
  *
  * NOTE: it only serves no-index type
@@ -1003,7 +1014,7 @@ static int fscache_cookies_seq_show(struct seq_file *m, void *v)
 		   "%08x %08x %5u %5u %3u %s %03lx %-16s %px",
 		   cookie->debug_id,
 		   cookie->parent ? cookie->parent->debug_id : 0,
-		   atomic_read(&cookie->usage),
+		   refcount_read(&cookie->ref),
 		   atomic_read(&cookie->n_children),
 		   atomic_read(&cookie->n_active),
 		   type,