linux-kernel - [PATCH v5 3/3] Add BUG_XX() debugging hard/soft lockup detection

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Date:	Mon,  1 Feb 2016 19:33:48 -0700
From:	Jeffrey Merkey <jeffmerkey@...il.com>
To:	linux-kernel@...r.kernel.org
Cc:	akpm@...ux-foundation.org, atomlin@...hat.com, cmetcalf@...hip.com,
	dzickus@...hat.com, fweisbec@...il.com,
	hidehiro.kawai.ez@...achi.com, mhocko@...e.cz, tj@...nel.org,
	uobergfe@...hat.com
Subject: [PATCH v5 3/3] Add BUG_XX() debugging hard/soft lockup detection

This patch series adds config options which can be set during compile to
direct the compiler to output a breakpoint instruction anywhere a BUG()
macro has been placed in the kernel to trigger the system to
enter a debugger if a bug is detected by the system.  Use of this
compile time option also allows conditional breakpoints to be set in the
kernel with these currently used macros.

This addition is extremely useful for debugging hard and soft lockups
real time and quickly from a console debugger, and other areas of the
kernel.

Signed-off-by: Jeffrey Merkey <jeffmerkey@...il.com>
---
 kernel/watchdog.c | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/kernel/watchdog.c b/kernel/watchdog.c
index b3ace6e..c504f7c 100644
--- a/kernel/watchdog.c
+++ b/kernel/watchdog.c
@@ -44,6 +44,12 @@
 #define NMI_WATCHDOG_ENABLED      (1 << NMI_WATCHDOG_ENABLED_BIT)
 #define SOFT_WATCHDOG_ENABLED     (1 << SOFT_WATCHDOG_ENABLED_BIT)
 
+#ifdef CONFIG_DEBUG_BUG
+#define WATCHDOG_DEBUG_LOCKUP  1
+#else
+#define WATCHDOG_DEBUG_LOCKUP  0
+#endif
+
 static DEFINE_MUTEX(watchdog_proc_mutex);
 
 #ifdef CONFIG_HARDLOCKUP_DETECTOR
@@ -358,6 +364,8 @@ static void watchdog_overflow_callback(struct perf_event *event,
 		else
 			dump_stack();
 
+		BUG_ON(WATCHDOG_DEBUG_LOCKUP);
+
 		/*
 		 * Perform all-CPU dump only once to avoid multiple hardlockups
 		 * generating interleaving traces
@@ -478,6 +486,8 @@ static enum hrtimer_restart watchdog_timer_fn(struct hrtimer *hrtimer)
 		else
 			dump_stack();
 
+		BUG_ON(WATCHDOG_DEBUG_LOCKUP);
+
 		if (softlockup_all_cpu_backtrace) {
 			/* Avoid generating two back traces for current
 			 * given that one is already made above
-- 
1.8.3.1