From: Matthew Dillon <dillon@apollo.backplane.com>
Date: Thu, 1 Dec 2011 23:22:44 +0000 (-0800)
Subject: kernel - Fix lost lock in devfs
X-Git-Tag: v3.0.0~514
X-Git-Url: http://gitweb.dragonflybsd.org/dragonfly.git/commitdiff_plain/495d3a1efd4f8832641e3489717539bbe8d72ebe

kernel - Fix lost lock in devfs

* vn_lock() will always fail if a vnode is undergoing reclamation, do
  not try to unlock/relock in the spec_close code in that case.

* Refactor the error test in devfs_allocv() in case vget() returns
  an error other than ENOENT in the future.
---

diff --git a/sys/vfs/devfs/devfs_core.c b/sys/vfs/devfs/devfs_core.c
index 8fd9992..8e4d9b8 100644
--- a/sys/vfs/devfs/devfs_core.c
+++ b/sys/vfs/devfs/devfs_core.c
@@ -295,10 +295,14 @@ devfs_allocv(struct vnode **vpp, struct devfs_node *node)
 try_again:
 	while ((vp = node->v_node) != NULL) {
 		error = vget(vp, LK_EXCLUSIVE);
-		if (error != ENOENT) {
+		if (error == 0) {
 			*vpp = vp;
 			goto out;
 		}
+		if (error != ENOENT) {
+			*vpp = NULL;
+			goto out;
+		}
 	}
 
 	if ((error = getnewvnode(VT_DEVFS, node->mp, vpp, 0, 0)) != 0)
diff --git a/sys/vfs/devfs/devfs_vnops.c b/sys/vfs/devfs/devfs_vnops.c
index dcc88fd..04638fb 100644
--- a/sys/vfs/devfs/devfs_vnops.c
+++ b/sys/vfs/devfs/devfs_vnops.c
@@ -1062,10 +1062,11 @@ devfs_spec_close(struct vop_close_args *ap)
 			node->flags |= DEVFS_INVISIBLE;
 
 		/*
-		 * Unlock around dev_dclose()
+		 * Unlock around dev_dclose(), unless the vnode is
+		 * undergoing a vgone/reclaim (during umount).
 		 */
 		needrelock = 0;
-		if (vn_islocked(vp)) {
+		if ((vp->v_flag & VRECLAIMED) == 0 && vn_islocked(vp)) {
 			needrelock = 1;
 			vn_unlock(vp);
 		}
@@ -1073,12 +1074,20 @@ devfs_spec_close(struct vop_close_args *ap)
 		/*
 		 * WARNING!  If the device destroys itself the devfs node
 		 *	     can disappear here.
+		 *
+		 * WARNING!  vn_lock() will fail if the vp is in a VRECLAIM,
+		 *	     which can occur during umount.
 		 */
 		error = dev_dclose(dev, ap->a_fflag, S_IFCHR);
 		/* node is now stale */
 
-		if (needrelock)
-			vn_lock(vp, LK_EXCLUSIVE | LK_RETRY);
+		if (needrelock) {
+			if (vn_lock(vp, LK_EXCLUSIVE | LK_RETRY) != 0) {
+				panic("devfs_spec_close: vnode %p "
+				      "unexpectedly could not be relocked",
+				      vp);
+			}
+		}
 	} else {
 		error = 0;
 	}