linux-kernel - [PATCH 01/31] Add hard/soft lockup debugger entry points

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Message-Id: <1454010366-28416-1-git-send-email-jeffmerkey@gmail.com>
Date:	Thu, 28 Jan 2016 12:46:06 -0700
From:	Jeffrey Merkey <jeffmerkey@...il.com>
To:	linux-kernel@...r.kernel.org
Cc:	akpm@...ux-foundation.org, dzickus@...hat.com, uobergfe@...hat.com,
	atomlin@...hat.com, mhocko@...e.cz, fweisbec@...il.com,
	tj@...nel.org, hidehiro.kawai.ez@...achi.com, cmetcalf@...hip.com
Subject: [PATCH 01/31] Add hard/soft lockup debugger entry points

This patch series adds an export which can be set by system debuggers to
direct the hard lockup and soft lockup detector to trigger a breakpoint
exception and enter a debugger if one is active.  It is assumed that if
someone sets this variable, then an breakpoint handler of some sort will
be actively loaded or registered via the notify die handler chain.

This addition is extremely useful for debugging hard and soft lockups
real time and quickly from a console debugger.

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..1dd5902 100644
--- a/kernel/watchdog.c
+++ b/kernel/watchdog.c
@@ -23,6 +23,7 @@
 #include <linux/workqueue.h>
 
 #include <asm/irq_regs.h>
+#include <asm/kdebug.h>
 #include <linux/kvm_para.h>
 #include <linux/perf_event.h>
 #include <linux/kthread.h>
@@ -108,6 +109,9 @@ static DEFINE_PER_CPU(struct perf_event *, watchdog_ev);
 #endif
 static unsigned long soft_lockup_nmi_warn;
 
+int debug_watchdog_lockups;
+EXPORT_SYMBOL_GPL(debug_watchdog_lockups);
+
 /* boot commands */
 /*
  * Should we panic when a soft-lockup or hard-lockup occurs:
@@ -358,6 +362,9 @@ static void watchdog_overflow_callback(struct perf_event *event,
 		else
 			dump_stack();
 
+		if (debug_watchdog_lockups)
+			arch_breakpoint();
+
 		/*
 		 * Perform all-CPU dump only once to avoid multiple hardlockups
 		 * generating interleaving traces
@@ -478,6 +485,9 @@ static enum hrtimer_restart watchdog_timer_fn(struct hrtimer *hrtimer)
 		else
 			dump_stack();
 
+		if (debug_watchdog_lockups)
+			arch_breakpoint();
+
 		if (softlockup_all_cpu_backtrace) {
 			/* Avoid generating two back traces for current
 			 * given that one is already made above
-- 
1.8.3.1