From 2390a1441effaba0e3d0f2f447f448aaf20428f1 Mon Sep 17 00:00:00 2001
From: Hans Petter Selasky <hselasky@FreeBSD.org>
Date: Tue, 2 Nov 2021 16:52:46 +0100
Subject: [PATCH] LinuxKPI: Add sysctl(8) knob to control verbosity of
 WARN_ON's.

The purpose of this change is to reduce the amount of dmesg(8) noise when
VT switching after a panic.

Submitted by:	Greg V <greg@unrelenting.technology>
MFC after:	1 week
Differential Revision:	https://reviews.freebsd.org/D30174
Sponsored by:	NVIDIA Networking
---
 .../linuxkpi/common/include/linux/kernel.h    | 25 +++++++++++--------
 sys/compat/linuxkpi/common/src/linux_compat.c |  5 ++++
 2 files changed, 19 insertions(+), 11 deletions(-)

diff --git a/sys/compat/linuxkpi/common/include/linux/kernel.h b/sys/compat/linuxkpi/common/include/linux/kernel.h
index 6cbd95c4ac6..94af8f29c4d 100644
--- a/sys/compat/linuxkpi/common/include/linux/kernel.h
+++ b/sys/compat/linuxkpi/common/include/linux/kernel.h
@@ -121,28 +121,31 @@ extern const volatile int lkpi_build_bug_on_zero;
 	}							\
 } while (0)
 
+extern int linuxkpi_warn_dump_stack;
 #define	WARN_ON(cond) ({					\
-      bool __ret = (cond);					\
-      if (__ret) {						\
+	bool __ret = (cond);					\
+	if (__ret) {						\
 		printf("WARNING %s failed at %s:%d\n",		\
 		    __stringify(cond), __FILE__, __LINE__);	\
-		linux_dump_stack();				\
-      }								\
-      unlikely(__ret);						\
+		if (linuxkpi_warn_dump_stack)				\
+			linux_dump_stack();				\
+	}								\
+	unlikely(__ret);						\
 })
 
 #define	WARN_ON_SMP(cond)	WARN_ON(cond)
 
 #define	WARN_ON_ONCE(cond) ({					\
-      static bool __warn_on_once;				\
-      bool __ret = (cond);					\
-      if (__ret && !__warn_on_once) {				\
+	static bool __warn_on_once;				\
+	bool __ret = (cond);					\
+	if (__ret && !__warn_on_once) {				\
 		__warn_on_once = 1;				\
 		printf("WARNING %s failed at %s:%d\n",		\
 		    __stringify(cond), __FILE__, __LINE__);	\
-		linux_dump_stack();				\
-      }								\
-      unlikely(__ret);						\
+		if (linuxkpi_warn_dump_stack)				\
+			linux_dump_stack();				\
+	}								\
+	unlikely(__ret);						\
 })
 
 #define	oops_in_progress	SCHEDULER_STOPPED()
diff --git a/sys/compat/linuxkpi/common/src/linux_compat.c b/sys/compat/linuxkpi/common/src/linux_compat.c
index a62cf93dbd8..6440f7bdcff 100644
--- a/sys/compat/linuxkpi/common/src/linux_compat.c
+++ b/sys/compat/linuxkpi/common/src/linux_compat.c
@@ -103,6 +103,11 @@ int linuxkpi_debug;
 SYSCTL_INT(_compat_linuxkpi, OID_AUTO, debug, CTLFLAG_RWTUN,
     &linuxkpi_debug, 0, "Set to enable pr_debug() prints. Clear to disable.");
 
+int linuxkpi_warn_dump_stack = 0;
+SYSCTL_INT(_compat_linuxkpi, OID_AUTO, warn_dump_stack, CTLFLAG_RWTUN,
+    &linuxkpi_warn_dump_stack, 0,
+    "Set to enable stack traces from WARN_ON(). Clear to disable.");
+
 static struct timeval lkpi_net_lastlog;
 static int lkpi_net_curpps;
 static int lkpi_net_maxpps = 99;