fuse: rcu-delay freeing fuse_conn

makes ->permission() and ->d_revalidate() safety in RCU mode independent
from vfsmount_lock.
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

fs/fuse/cuse.c

@@ -473,7 +473,7 @@ static int cuse_send_init(struct cuse_conn *cc)
 static void cuse_fc_release(struct fuse_conn *fc)
 {
 	struct cuse_conn *cc = fc_to_cc(fc);
-	kfree(cc);
+	kfree_rcu(cc, fc.rcu);
 }
 
 /**

fs/fuse/fuse_i.h

@@ -377,6 +377,8 @@ struct fuse_conn {
 	/** Refcount */
 	atomic_t count;
 
+	struct rcu_head rcu;
+
 	/** The user id for this mount */
 	kuid_t user_id;
 

fs/fuse/inode.c

@@ -918,7 +918,7 @@ static void fuse_send_init(struct fuse_conn *fc, struct fuse_req *req)
 
 static void fuse_free_conn(struct fuse_conn *fc)
 {
-	kfree(fc);
+	kfree_rcu(fc, rcu);
 }
 
 static int fuse_bdi_init(struct fuse_conn *fc, struct super_block *sb)