From 3d3de5ce17df9092e3104c56cff532611e782529 Mon Sep 17 00:00:00 2001
From: kib <kib@FreeBSD.org>
Date: Thu, 26 Nov 2020 18:16:32 +0000
Subject: [PATCH] nullfs: provide custom bypass for VOP_READ_PGCACHE().

Normal bypass expects locked vnode, which is not true for
VOP_READ_PGCACHE().  Ensure liveness of the lower vnode by taking the
upper vnode interlock, which is also taked by null_reclaim() when
setting v_data to NULL.

Reported and tested by:	pho
Reviewed by:	markj, mjg
Sponsored by:	The FreeBSD Foundation
Differential revision:	https://reviews.freebsd.org/D27327
---
 sys/fs/nullfs/null_vnops.c | 23 +++++++++++++++++++++++
 1 file changed, 23 insertions(+)

diff --git a/sys/fs/nullfs/null_vnops.c b/sys/fs/nullfs/null_vnops.c
index d10337865744..b79bbb96e371 100644
--- a/sys/fs/nullfs/null_vnops.c
+++ b/sys/fs/nullfs/null_vnops.c
@@ -947,6 +947,28 @@ null_vptocnp(struct vop_vptocnp_args *ap)
 	return (error);
 }
 
+static int
+null_read_pgcache(struct vop_read_pgcache_args *ap)
+{
+	struct vnode *lvp, *vp;
+	struct null_node *xp;
+	int error;
+
+	vp = ap->a_vp;
+	VI_LOCK(vp);
+	xp = VTONULL(vp);
+	if (xp == NULL) {
+		VI_UNLOCK(vp);
+		return (EJUSTRETURN);
+	}
+	lvp = xp->null_lowervp;
+	vref(lvp);
+	VI_UNLOCK(vp);
+	error = VOP_READ_PGCACHE(lvp, ap->a_uio, ap->a_ioflag, ap->a_cred);
+	vrele(lvp);
+	return (error);
+}
+
 /*
  * Global vfs data structures
  */
@@ -966,6 +988,7 @@ struct vop_vector null_vnodeops = {
 	.vop_lookup =		null_lookup,
 	.vop_open =		null_open,
 	.vop_print =		null_print,
+	.vop_read_pgcache =	null_read_pgcache,
 	.vop_reclaim =		null_reclaim,
 	.vop_remove =		null_remove,
 	.vop_rename =		null_rename,