From: anton <anton@openbsd.org>
Date: Tue, 28 Dec 2021 17:50:10 +0000 (+0000)
Subject: The initial kd_lookup() in kcovopen() is redundant as kcov is a cloning
X-Git-Url: http://artulab.com/gitweb/?a=commitdiff_plain;h=81a83fa0ac51834161c07d1060db5f8c94a8ec60;p=openbsd

The initial kd_lookup() in kcovopen() is redundant as kcov is a cloning
device. Turn it into an assertion instead to better state the expected
semantics of D_CLONE.

Prompted after a discussion with visa@
---

diff --git a/sys/dev/kcov.c b/sys/dev/kcov.c
index 0a130fd0c25..5db7e764786 100644
--- a/sys/dev/kcov.c
+++ b/sys/dev/kcov.c
@@ -1,4 +1,4 @@
-/*	$OpenBSD: kcov.c,v 1.42 2021/12/27 15:38:25 anton Exp $	*/
+/*	$OpenBSD: kcov.c,v 1.43 2021/12/28 17:50:10 anton Exp $	*/
 
 /*
  * Copyright (c) 2018 Anton Lindqvist <anton@openbsd.org>
@@ -53,7 +53,7 @@
 struct kcov_dev {
 	int		 kd_state;	/* [M] */
 	int		 kd_mode;	/* [M] */
-	int		 kd_unit;	/* [I] device minor */
+	int		 kd_unit;	/* [I] D_CLONE unique device minor */
 	int		 kd_intr;	/* [M] currently used in interrupt */
 	uintptr_t	*kd_buf;	/* [a] traced coverage */
 	size_t		 kd_nmemb;	/* [I] */
@@ -290,21 +290,13 @@ kcovopen(dev_t dev, int flag, int mode, struct proc *p)
 {
 	struct kcov_dev *kd;
 
-	mtx_enter(&kcov_mtx);
-
-	if (kd_lookup(minor(dev)) != NULL) {
-		mtx_leave(&kcov_mtx);
-		return (EBUSY);
-	}
-
-	if (kcov_cold)
-		kcov_cold = 0;
-
-	mtx_leave(&kcov_mtx);
 	kd = malloc(sizeof(*kd), M_SUBPROC, M_WAITOK | M_ZERO);
 	kd->kd_unit = minor(dev);
 	mtx_enter(&kcov_mtx);
+	KASSERT(kd_lookup(kd->kd_unit) == NULL);
 	TAILQ_INSERT_TAIL(&kd_list, kd, kd_entry);
+	if (kcov_cold)
+		kcov_cold = 0;
 	mtx_leave(&kcov_mtx);
 	return (0);
 }