From 1121a37474fd5e864b744fd220a1bcb78ed66fae Mon Sep 17 00:00:00 2001
From: Konstantin Belousov <kib@FreeBSD.org>
Date: Wed, 1 Nov 2017 11:37:45 +0000
Subject: [PATCH] Be protective and check the po_file validity before dropping
 the ref.

Reported and tested by:	pho
Reviewed by:	markj
Sponsored by:	The FreeBSD Foundation
MFC after:	1 week
X-Differential revision:	https://reviews.freebsd.org/D12882
---
 sys/dev/hwpmc/hwpmc_logging.c | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/sys/dev/hwpmc/hwpmc_logging.c b/sys/dev/hwpmc/hwpmc_logging.c
index 7b19bd4ef652..bfd831b69908 100644
--- a/sys/dev/hwpmc/hwpmc_logging.c
+++ b/sys/dev/hwpmc/hwpmc_logging.c
@@ -681,8 +681,11 @@ pmclog_deconfigure_log(struct pmc_owner *po)
 	}
 
 	/* drop a reference to the fd */
-	error = fdrop(po->po_file, curthread);
-	po->po_file  = NULL;
+	if (po->po_file != NULL) {
+		error = fdrop(po->po_file, curthread);
+		po->po_file  = NULL;
+	} else
+		error = 0;
 	po->po_error = 0;
 
 	return (error);