From f8f7dc1f1132b5aeb0dfc6c92da9ba96b923f6b9 Mon Sep 17 00:00:00 2001
From: bluhm <bluhm@openbsd.org>
Date: Wed, 25 Sep 2024 18:24:13 +0000
Subject: [PATCH] Do not crash in witness code if interrupt fires early.

It can happen that an interrupt handler is called immediately on a
secondary CPU when it is spun up during boot.  At that moment no
process is schduled yet, so curproc is NULL.  To prevent a crash
when p->p_sleeplocks is dereferenced, skip witness check in this
case.

OK visa@
---
 sys/kern/subr_witness.c | 33 ++++++++++++++++++++-------------
 1 file changed, 20 insertions(+), 13 deletions(-)

diff --git a/sys/kern/subr_witness.c b/sys/kern/subr_witness.c
index 9f0919013b2..7110414f25c 100644
--- a/sys/kern/subr_witness.c
+++ b/sys/kern/subr_witness.c
@@ -1,4 +1,4 @@
-/*	$OpenBSD: subr_witness.c,v 1.53 2024/06/03 14:34:19 claudio Exp $	*/
+/*	$OpenBSD: subr_witness.c,v 1.54 2024/09/25 18:24:13 bluhm Exp $	*/
 
 /*-
  * Copyright (c) 2008 Isilon Systems, Inc.
@@ -766,7 +766,6 @@ witness_checkorder(struct lock_object *lock, int flags,
 	struct lock_list_entry *lock_list, *lle;
 	struct lock_instance *lock1, *lock2, *plock;
 	struct lock_class *class, *iclass;
-	struct proc *p;
 	struct witness *w, *w1;
 	int i, j, s;
 
@@ -792,9 +791,9 @@ witness_checkorder(struct lock_object *lock, int flags,
 		w = lock->lo_witness =
 		    enroll(lock->lo_type, lock->lo_name, class);
 
-	p = curproc;
-
 	if (class->lc_flags & LC_SLEEPLOCK) {
+		struct proc *p;
+
 		/*
 		 * Since spin locks include a critical section, this check
 		 * implicitly enforces a lock order of all sleep locks before
@@ -811,6 +810,9 @@ witness_checkorder(struct lock_object *lock, int flags,
 		 * If this is the first lock acquired then just return as
 		 * no order checking is needed.
 		 */
+		p = curproc;
+		if (p == NULL)
+			return;
 		lock_list = p->p_sleeplocks;
 		if (lock_list == NULL || lock_list->ll_count == 0)
 			return;
@@ -1097,7 +1099,6 @@ witness_lock(struct lock_object *lock, int flags)
 {
 	struct lock_list_entry **lock_list, *lle;
 	struct lock_instance *instance;
-	struct proc *p;
 	struct witness *w;
 	int s;
 
@@ -1110,12 +1111,15 @@ witness_lock(struct lock_object *lock, int flags)
 		w = lock->lo_witness =
 		    enroll(lock->lo_type, lock->lo_name, LOCK_CLASS(lock));
 
-	p = curproc;
-
 	/* Determine lock list for this lock. */
-	if (LOCK_CLASS(lock)->lc_flags & LC_SLEEPLOCK)
+	if (LOCK_CLASS(lock)->lc_flags & LC_SLEEPLOCK) {
+		struct proc *p;
+
+		p = curproc;
+		if (p == NULL)
+			return;
 		lock_list = &p->p_sleeplocks;
-	else
+	} else
 		lock_list = &witness_cpu[cpu_number()].wc_spinlocks;
 
 	s = splhigh();
@@ -1243,20 +1247,23 @@ witness_unlock(struct lock_object *lock, int flags)
 	struct lock_list_entry **lock_list, *lle;
 	struct lock_instance *instance;
 	struct lock_class *class;
-	struct proc *p;
 	int i, j;
 	int s;
 
 	if (witness_cold || lock->lo_witness == NULL ||
 	    panicstr != NULL || db_active)
 		return;
-	p = curproc;
 	class = LOCK_CLASS(lock);
 
 	/* Find lock instance associated with this lock. */
-	if (class->lc_flags & LC_SLEEPLOCK)
+	if (class->lc_flags & LC_SLEEPLOCK) {
+		struct proc *p;
+
+		p = curproc;
+		if (p == NULL)
+			return;
 		lock_list = &p->p_sleeplocks;
-	else
+	} else
 		lock_list = &witness_cpu[cpu_number()].wc_spinlocks;
 
 	s = splhigh();
-- 
2.20.1