From 0af463e6619cf9f7386129d427c244d3da30fa3a Mon Sep 17 00:00:00 2001
From: Konstantin Belousov <kib@FreeBSD.org>
Date: Sat, 5 Feb 2022 04:03:47 +0200
Subject: [PATCH] ffs_read(): lock buffers after snaplk with LK_NOWITNESS

Reviewed and tested by:	mckusick
Sponsored by:	The FreeBSD Foundation
MFC after:	1 week
Differential revision:	https://reviews.freebsd.org/D34179
---
 sys/ufs/ffs/ffs_vnops.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/sys/ufs/ffs/ffs_vnops.c b/sys/ufs/ffs/ffs_vnops.c
index 66dafed5ac9e..b57e9a3a71b0 100644
--- a/sys/ufs/ffs/ffs_vnops.c
+++ b/sys/ufs/ffs/ffs_vnops.c
@@ -695,6 +695,9 @@ ffs_read(ap)
 		return (EOVERFLOW);
 
 	bflag = GB_UNMAPPED | (uio->uio_segflg == UIO_NOCOPY ? 0 : GB_NOSPARSE);
+#ifdef WITNESS
+	bflag |= IS_SNAPSHOT(ip) ? GB_NOWITNESS : 0;
+#endif
 	for (error = 0, bp = NULL; uio->uio_resid > 0; bp = NULL) {
 		if ((bytesinfile = ip->i_size - uio->uio_offset) <= 0)
 			break;