From 99c66d3acf539e25ce9978c16e4dda3940c041fb Mon Sep 17 00:00:00 2001
From: Konstantin Belousov <kib@FreeBSD.org>
Date: Thu, 26 Nov 2020 18:13:33 +0000
Subject: [PATCH] vn_read_from_obj(): fix handling of doomed vnodes.

There is no reason why vp->v_object cannot be NULL. If it is, it's
fine, handle it by delegating to VOP_READ().

Tested by:	pho
Reviewed by:	markj, mjg
Sponsored by:	The FreeBSD Foundation
Differential revision:	https://reviews.freebsd.org/D27327
---
 sys/kern/vfs_vnops.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/sys/kern/vfs_vnops.c b/sys/kern/vfs_vnops.c
index f65d44122af..832ff9ac34a 100644
--- a/sys/kern/vfs_vnops.c
+++ b/sys/kern/vfs_vnops.c
@@ -870,10 +870,10 @@ vn_read_from_obj(struct vnode *vp, struct uio *uio)
 	ssize_t resid;
 	int error, i, j;
 
-	obj = vp->v_object;
 	MPASS(uio->uio_resid <= ptoa(io_hold_cnt + 2));
-	MPASS(obj != NULL);
-	MPASS(obj->type == OBJT_VNODE);
+	obj = atomic_load_ptr(&vp->v_object);
+	if (obj == NULL)
+		return (EJUSTRETURN);
 
 	/*
 	 * Depends on type stability of vm_objects.