p9fs: use atomics for updating node->flags

This should prevent seeing inconsistent flags values when updating it
under the shared vnode lock.

Noted and reviewed by:	markj
Sponsored by:	The FreeBSD Foundation
MFC after:	1 week
Differential revision:	https://reviews.freebsd.org/D55665

sys/fs/p9fs/p9fs.h

@@ -103,7 +103,7 @@ struct p9fs_node {
 	struct p9fs_inode inode;		/* in memory representation of ondisk information*/
 	struct p9fs_session *p9fs_ses;	/*  Session_ptr for this node */
 	STAILQ_ENTRY(p9fs_node) p9fs_node_next;
-	uint64_t flags;
+	u_int flags;
 };
 
 #define P9FS_VTON(vp) ((struct p9fs_node *)(vp)->v_data)
@@ -111,10 +111,13 @@ struct p9fs_node {
 #define	VFSTOP9(mp) ((struct p9fs_mount *)(mp)->mnt_data)
 #define QEMU_DIRENTRY_SZ	25
 #define P9FS_NODE_MODIFIED	0x1  /* indicating file change */
-#define P9FS_ROOT		0x2  /* indicating root p9fs node */
+#define P9FS_NODE_ROOT		0x2  /* indicating root p9fs node */
 #define P9FS_NODE_DELETED	0x4  /* indicating file or directory delete */
 #define P9FS_NODE_IN_SESSION	0x8  /* p9fs_node is in the session - virt_node_list */
-#define IS_ROOT(node)	(node->flags & P9FS_ROOT)
+#define IS_ROOT(node)	(((node)->flags & P9FS_NODE_ROOT) != 0)
+
+#define	P9FS_NODE_SETF(n, f)	atomic_set_int(&(n)->flags, (f))
+#define	P9FS_NODE_CLRF(n, f)	atomic_clear_int(&(n)->flags, (f))
 
 #define P9FS_SET_LINKS(inode) do {	\
 	(inode)->i_links_count = 1;	\

sys/fs/p9fs/p9fs_vfsops.c

@@ -284,7 +284,7 @@ p9fs_vget_common(struct mount *mp, struct p9fs_node *np, int flags,
 			node = vp->v_data;
 			/* Remove stale vnode from hash list */
 			vfs_hash_remove(vp);
-			node->flags |= P9FS_NODE_DELETED;
+			P9FS_NODE_SETF(node, P9FS_NODE_DELETED);
 
 			vput(vp);
 			*vpp = NULL;
@@ -372,7 +372,7 @@ p9fs_vget_common(struct mount *mp, struct p9fs_node *np, int flags,
 	if (*vpp == NULL) {
 		P9FS_LOCK(vses);
 		STAILQ_INSERT_TAIL(&vses->virt_node_list, np, p9fs_node_next);
-		np->flags |= P9FS_NODE_IN_SESSION;
+		P9FS_NODE_SETF(np, P9FS_NODE_IN_SESSION);
 		P9FS_UNLOCK(vses);
 		vn_set_state(vp, VSTATE_CONSTRUCTED);
 		*vpp = vp;
@@ -448,7 +448,7 @@ p9_mount(struct mount *mp)
 	P9FS_VOFID_LOCK_INIT(p9fs_root);
 	STAILQ_INIT(&p9fs_root->vofid_list);
 	p9fs_root->parent = p9fs_root;
-	p9fs_root->flags |= P9FS_ROOT;
+	P9FS_NODE_SETF(p9fs_root, P9FS_NODE_ROOT);
 	p9fs_root->p9fs_ses = vses;
 	vfs_getnewfsid(mp);
 	strlcpy(mp->mnt_stat.f_mntfromname, from,

sys/fs/p9fs/p9fs_vnops.c

@@ -111,7 +111,7 @@ p9fs_cleanup(struct p9fs_node *np)
 
 	P9FS_LOCK(vses);
 	if ((np->flags & P9FS_NODE_IN_SESSION) != 0) {
-		np->flags &= ~P9FS_NODE_IN_SESSION;
+		P9FS_NODE_CLRF(np, P9FS_NODE_IN_SESSION);
 		STAILQ_REMOVE(&vses->virt_node_list, np, p9fs_node, p9fs_node_next);
 	} else {
 		P9FS_UNLOCK(vses);
@@ -675,7 +675,7 @@ p9fs_open(struct vop_open_args *ap)
 		error = vinvalbuf(vp, 0, 0, 0);
 		if (error != 0)
 			return (error);
-		np->flags &= ~P9FS_NODE_MODIFIED;
+		P9FS_NODE_CLRF(np, P9FS_NODE_MODIFIED);
 	}
 
 	vfid = p9fs_get_fid(vses->clnt, np, ap->a_cred, VFID, -1, &error);
@@ -1003,7 +1003,7 @@ p9fs_stat_vnode_dotl(struct p9_stat_dotl *stat, struct vnode *vp)
 
 	/* Setting a flag if file changes based on qid version */
 	if (np->vqid.qid_version != stat->qid.version)
-		np->flags |= P9FS_NODE_MODIFIED;
+		P9FS_NODE_SETF(np, P9FS_NODE_MODIFIED);
 	memcpy(&np->vqid, &stat->qid, sizeof(stat->qid));
 	if (!excl_locked)
 		VI_UNLOCK(vp);
@@ -1549,7 +1549,7 @@ remove_common(struct p9fs_node *dnp, struct p9fs_node *np, const char *name,
 	cache_purge(vp);
 	vfs_hash_remove(vp);
 
-	np->flags |= P9FS_NODE_DELETED;
+	P9FS_NODE_SETF(np, P9FS_NODE_DELETED);
 
 	return (error);
 }