svn commit: r368077 - head/sys/fs/nullfs

[Konstantin Belousov]

Author: kib
Date: Thu Nov 26 18:16:32 2020
New Revision: 368077
URL: https://svnweb.freebsd.org/changeset/base/368077

Log:
  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

Modified:
  head/sys/fs/nullfs/null_vnops.c

Modified: head/sys/fs/nullfs/null_vnops.c
==============================================================================
--- head/sys/fs/nullfs/null_vnops.c	Thu Nov 26 18:13:33 2020	(r368076)
+++ head/sys/fs/nullfs/null_vnops.c	Thu Nov 26 18:16:32 2020	(r368077)
@@ -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,