afs: Make vnode->cb_interest RCU safe

Use RCU-based freeing for afs_cb_interest struct objects and use RCU on
vnode->cb_interest.  Use that change to allow afs_check_validity() to use
read_seqbegin_or_lock() instead of read_seqlock_excl().

This also requires the caller of afs_check_validity() to hold the RCU read
lock across the call.

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

1 files changed, 12 insertions, 9 deletions

diff --git a/fs/afs/callback.c b/fs/afs/callback.c
index 4876079aa643..d441bef72163 100644
--- a/fs/afs/callback.c
+++ b/fs/afs/callback.c
@@ -94,15 +94,15 @@ int afs_register_server_cb_interest(struct afs_vnode *vnode,
 	struct afs_server *server = entry->server;
 
 again:
-	if (vnode->cb_interest &&
-	    likely(vnode->cb_interest == entry->cb_interest))
+	vcbi = rcu_dereference_protected(vnode->cb_interest,
+					 lockdep_is_held(&vnode->io_lock));
+	if (vcbi && likely(vcbi == entry->cb_interest))
 		return 0;
 
 	read_lock(&slist->lock);
 	cbi = afs_get_cb_interest(entry->cb_interest);
 	read_unlock(&slist->lock);
 
-	vcbi = vnode->cb_interest;
 	if (vcbi) {
 		if (vcbi == cbi) {
 			afs_put_cb_interest(afs_v2net(vnode), cbi);
@@ -114,8 +114,9 @@ again:
 		 */
 		if (cbi && vcbi->server == cbi->server) {
 			write_seqlock(&vnode->cb_lock);
-			old = vnode->cb_interest;
-			vnode->cb_interest = cbi;
+			old = rcu_dereference_protected(vnode->cb_interest,
+							lockdep_is_held(&vnode->cb_lock.lock));
+			rcu_assign_pointer(vnode->cb_interest, cbi);
 			write_sequnlock(&vnode->cb_lock);
 			afs_put_cb_interest(afs_v2net(vnode), old);
 			return 0;
@@ -160,8 +161,9 @@ again:
 	 */
 	write_seqlock(&vnode->cb_lock);
 
-	old = vnode->cb_interest;
-	vnode->cb_interest = cbi;
+	old = rcu_dereference_protected(vnode->cb_interest,
+					lockdep_is_held(&vnode->cb_lock.lock));
+	rcu_assign_pointer(vnode->cb_interest, cbi);
 	vnode->cb_s_break = cbi->server->cb_s_break;
 	vnode->cb_v_break = vnode->volume->cb_v_break;
 	clear_bit(AFS_VNODE_CB_PROMISED, &vnode->flags);
@@ -191,10 +193,11 @@ void afs_put_cb_interest(struct afs_net *net, struct afs_cb_interest *cbi)
 				vi = NULL;
 
 			write_unlock(&cbi->server->cb_break_lock);
-			kfree(vi);
+			if (vi)
+				kfree_rcu(vi, rcu);
 			afs_put_server(net, cbi->server);
 		}
-		kfree(cbi);
+		kfree_rcu(cbi, rcu);
 	}
 }