From 42a9f8f21d636f38a2d71b7a84a686eb436886f9 Mon Sep 17 00:00:00 2001
From: Mateusz Guzik <mjg@FreeBSD.org>
Date: Thu, 30 Jan 2020 02:16:17 +0000
Subject: [PATCH] zfs: fix spurious lock contention during path lookup

ZFS tracks if anything denies VEXEC to allow for a quick check for the
common case of path traversal. Use it.

Differential Revision:	https://reviews.freebsd.org/D22224
---
 .../uts/common/fs/zfs/sys/zfs_acl.h           |  3 ++
 .../opensolaris/uts/common/fs/zfs/zfs_acl.c   | 35 +++++++++++++++++++
 .../opensolaris/uts/common/fs/zfs/zfs_vnops.c |  5 +++
 3 files changed, 43 insertions(+)

diff --git a/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/sys/zfs_acl.h b/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/sys/zfs_acl.h
index 48f55a03f19..b34360a3c82 100644
--- a/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/sys/zfs_acl.h
+++ b/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/sys/zfs_acl.h
@@ -214,7 +214,10 @@ void zfs_oldace_byteswap(ace_t *, int);
 void zfs_ace_byteswap(void *, size_t, boolean_t);
 extern boolean_t zfs_has_access(struct znode *zp, cred_t *cr);
 extern int zfs_zaccess(struct znode *, int, int, boolean_t, cred_t *);
+#ifdef illumos
 int zfs_fastaccesschk_execute(struct znode *, cred_t *);
+#endif
+int zfs_freebsd_fastaccesschk_execute(struct vnode *, cred_t *);
 extern int zfs_zaccess_rwx(struct znode *, mode_t, int, cred_t *);
 extern int zfs_zaccess_unix(struct znode *, mode_t, cred_t *);
 extern int zfs_acl_access(struct znode *, int, cred_t *);
diff --git a/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/zfs_acl.c b/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/zfs_acl.c
index 6332559edd7..6527b5878e6 100644
--- a/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/zfs_acl.c
+++ b/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/zfs_acl.c
@@ -2299,6 +2299,40 @@ zfs_zaccess_append(znode_t *zp, uint32_t *working_mode, boolean_t *check_privs,
 	    check_privs, B_FALSE, cr));
 }
 
+/*
+ * Check if VEXEC is allowed.
+ *
+ * This routine is based on zfs_fastaccesschk_execute which has slowpath
+ * calling zfs_zaccess. This would be incorrect on FreeBSD (see
+ * zfs_freebsd_access for the difference). Thus this variant let's the
+ * caller handle the slowpath (if necessary).
+ *
+ * We only check for ZFS_NO_EXECS_DENIED and fail early. This routine can
+ * be extended to cover more cases, but the flag covers the majority.
+ */
+int
+zfs_freebsd_fastaccesschk_execute(struct vnode *vp, cred_t *cr)
+{
+	boolean_t is_attr;
+	znode_t *zdp = VTOZ(vp);
+
+	ASSERT_VOP_LOCKED(vp, __func__);
+
+	if (zdp->z_pflags & ZFS_AV_QUARANTINED)
+		return (1);
+
+	is_attr = ((zdp->z_pflags & ZFS_XATTR) &&
+	    (ZTOV(zdp)->v_type == VDIR));
+	if (is_attr)
+		return (1);
+
+	if (zdp->z_pflags & ZFS_NO_EXECS_DENIED)
+		return (0);
+
+	return (1);
+}
+
+#ifdef illumos
 int
 zfs_fastaccesschk_execute(znode_t *zdp, cred_t *cr)
 {
@@ -2365,6 +2399,7 @@ zfs_fastaccesschk_execute(znode_t *zdp, cred_t *cr)
 	ZFS_EXIT(zdp->z_zfsvfs);
 	return (error);
 }
+#endif
 
 /*
  * Determine whether Access should be granted/denied.
diff --git a/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/zfs_vnops.c b/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/zfs_vnops.c
index 3ddd22507e9..cd39ad56e24 100644
--- a/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/zfs_vnops.c
+++ b/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/zfs_vnops.c
@@ -4858,6 +4858,11 @@ zfs_freebsd_access(ap)
 	accmode_t accmode;
 	int error = 0;
 
+	if (ap->a_accmode == VEXEC) {
+		if (zfs_freebsd_fastaccesschk_execute(ap->a_vp, ap->a_cred) == 0)
+			return (0);
+	}
+
 	/*
 	 * ZFS itself only knowns about VREAD, VWRITE, VEXEC and VAPPEND,
 	 */
-- 
2.45.0