[PATCH][RT] stacktrace: dump out last preempt disable locations

From: Steven Rostedt
Date: Thu Jul 30 2009 - 22:29:21 EST

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Thomas,

This patch was somehow dropped from the 31-rt port. It is very useful
since it shows the last locations that preemption was disabled. The bugs
that Darren and Clark are seeing would probably be spotted by this patch.
Could you add it back.

Ingo wrote the original version of this code, but as things changed I
needed to rewrite it.

-- Steve

-----
Track preempt disable nesting

This code was largly influenced by work from Ingo Molnar.

Signed-off-by: Steven Rostedt <srostedt@xxxxxxxxxx>
---
arch/arm/kernel/traps.c | 1 +
include/linux/preempt.h | 3 ++-
include/linux/sched.h | 11 +++++++++++
kernel/sched.c | 17 +++++++++++++++--
kernel/trace/Kconfig | 8 ++++++++
kernel/trace/Makefile | 2 ++
kernel/trace/preempt-trace.c | 30 ++++++++++++++++++++++++++++++
7 files changed, 69 insertions(+), 3 deletions(-)

Index: linux-2.6.31-rc4-rt1/arch/arm/kernel/traps.c
===================================================================
--- linux-2.6.31-rc4-rt1.orig/arch/arm/kernel/traps.c 2009-07-30 21:28:57.000000000 -0400
+++ linux-2.6.31-rc4-rt1/arch/arm/kernel/traps.c 2009-07-30 21:30:58.000000000 -0400
@@ -365,6 +365,7 @@ asmlinkage void do_unexp_fiq (struct pt_
{
printk("Hmm. Unexpected FIQ received, but trying to continue\n");
printk("You may have a hardware problem...\n");
+ print_preempt_trace(current);
}

/*
Index: linux-2.6.31-rc4-rt1/include/linux/preempt.h
===================================================================
--- linux-2.6.31-rc4-rt1.orig/include/linux/preempt.h 2009-07-30 21:28:58.000000000 -0400
+++ linux-2.6.31-rc4-rt1/include/linux/preempt.h 2009-07-30 21:30:58.000000000 -0400
@@ -10,7 +10,8 @@
#include <linux/linkage.h>
#include <linux/list.h>

-#if defined(CONFIG_DEBUG_PREEMPT) || defined(CONFIG_PREEMPT_TRACER)
+#if defined(CONFIG_DEBUG_PREEMPT) || defined(CONFIG_PREEMPT_TRACER) || \
+ defined(CONFIG_PREEMPT_TRACE)
extern void add_preempt_count(int val);
extern void sub_preempt_count(int val);
#else
Index: linux-2.6.31-rc4-rt1/include/linux/sched.h
===================================================================
--- linux-2.6.31-rc4-rt1.orig/include/linux/sched.h 2009-07-30 21:28:58.000000000 -0400
+++ linux-2.6.31-rc4-rt1/include/linux/sched.h 2009-07-30 21:33:50.000000000 -0400
@@ -1437,6 +1437,11 @@ struct task_struct {

#define MAX_PREEMPT_TRACE 25
#define MAX_LOCK_STACK MAX_PREEMPT_TRACE
+#ifdef CONFIG_PREEMPT_TRACE
+ unsigned long preempt_trace_eip[MAX_PREEMPT_TRACE];
+ unsigned long preempt_trace_parent_eip[MAX_PREEMPT_TRACE];
+#endif
+
#ifdef CONFIG_DEBUG_PREEMPT
atomic_t lock_count;
# ifdef CONFIG_PREEMPT_RT
@@ -2605,6 +2610,12 @@ static inline int task_is_current(struct
}
#endif

+#ifdef CONFIG_PREEMPT_TRACE
+void print_preempt_trace(struct task_struct *tsk);
+#else
+static inline void print_preempt_trace(struct task_struct *tsk) { }
+#endif
+
#endif /* __KERNEL__ */

#endif
Index: linux-2.6.31-rc4-rt1/kernel/sched.c
===================================================================
--- linux-2.6.31-rc4-rt1.orig/kernel/sched.c 2009-07-30 21:28:58.000000000 -0400
+++ linux-2.6.31-rc4-rt1/kernel/sched.c 2009-07-30 22:01:03.000000000 -0400
@@ -5349,10 +5349,14 @@ EXPORT_SYMBOL(preempt_enable_no_resched)
#endif

#if defined(CONFIG_PREEMPT) && (defined(CONFIG_DEBUG_PREEMPT) || \
- defined(CONFIG_PREEMPT_TRACER))
+ defined(CONFIG_PREEMPT_TRACER) || \
+ defined(CONFIG_PREEMPT_TRACE))

void __kprobes add_preempt_count(int val)
{
+ unsigned long eip = CALLER_ADDR0;
+ unsigned long parent_eip = get_parent_ip(CALLER_ADDR1);
+
#ifdef CONFIG_DEBUG_PREEMPT
/*
* Underflow?
@@ -5361,6 +5365,15 @@ void __kprobes add_preempt_count(int val
return;
#endif
preempt_count() += val;
+#ifdef CONFIG_PREEMPT_TRACE
+ if (val <= 10) {
+ unsigned int idx = preempt_count() & PREEMPT_MASK;
+ if (idx < MAX_PREEMPT_TRACE) {
+ current->preempt_trace_eip[idx] = eip;
+ current->preempt_trace_parent_eip[idx] = parent_eip;
+ }
+ }
+#endif
#ifdef CONFIG_DEBUG_PREEMPT
/*
* Spinlock count overflowing soon?
@@ -5369,7 +5382,7 @@ void __kprobes add_preempt_count(int val
PREEMPT_MASK - 10);
#endif
if (preempt_count() == val)
- trace_preempt_off(CALLER_ADDR0, get_parent_ip(CALLER_ADDR1));
+ trace_preempt_off(eip, parent_eip);
}
EXPORT_SYMBOL(add_preempt_count);

Index: linux-2.6.31-rc4-rt1/kernel/trace/Kconfig
===================================================================
--- linux-2.6.31-rc4-rt1.orig/kernel/trace/Kconfig 2009-07-30 21:28:58.000000000 -0400
+++ linux-2.6.31-rc4-rt1/kernel/trace/Kconfig 2009-07-30 21:36:14.000000000 -0400
@@ -502,6 +502,14 @@ config RING_BUFFER_BENCHMARK

If unsure, say N

+config PREEMPT_TRACE
+ bool "Keep a record of preempt disabled spots"
+ depends on DEBUG_KERNEL
+ depends on PREEMPT
+ select TRACING
+ help
+ Keeps a record of the last 25 preempt disabled locations.
+
endif # FTRACE

endif # TRACING_SUPPORT
Index: linux-2.6.31-rc4-rt1/kernel/trace/Makefile
===================================================================
--- linux-2.6.31-rc4-rt1.orig/kernel/trace/Makefile 2009-07-30 21:26:32.000000000 -0400
+++ linux-2.6.31-rc4-rt1/kernel/trace/Makefile 2009-07-30 21:34:40.000000000 -0400
@@ -55,4 +55,6 @@ obj-$(CONFIG_FTRACE_SYSCALLS) += trace_s
obj-$(CONFIG_EVENT_PROFILE) += trace_event_profile.o
obj-$(CONFIG_EVENT_TRACING) += trace_events_filter.o

+obj-$(CONFIG_PREEMPT_TRACE) += preempt-trace.o
+
libftrace-y := ftrace.o
Index: linux-2.6.31-rc4-rt1/kernel/trace/preempt-trace.c
===================================================================
--- /dev/null 1970-01-01 00:00:00.000000000 +0000
+++ linux-2.6.31-rc4-rt1/kernel/trace/preempt-trace.c 2009-07-30 21:30:58.000000000 -0400
@@ -0,0 +1,30 @@
+#include <linux/sched.h>
+#include <linux/hardirq.h>
+#include <linux/kallsyms.h>
+
+void print_preempt_trace(struct task_struct *task)
+{
+ unsigned int count;
+ unsigned int i, lim;
+
+ if (!task)
+ task = current;
+
+ count = task_thread_info(task)->preempt_count;
+ lim = count & PREEMPT_MASK;
+
+ if (lim >= MAX_PREEMPT_TRACE)
+ lim = MAX_PREEMPT_TRACE-1;
+ printk("---------------------------\n");
+ printk("| preempt count: %08x ]\n", count);
+ printk("| %d-level deep critical section nesting:\n", lim);
+ printk("----------------------------------------\n");
+ for (i = 1; i <= lim; i++) {
+ printk(".. [<%08lx>] .... ", task->preempt_trace_eip[i]);
+ print_symbol("%s\n", task->preempt_trace_eip[i]);
+ printk(".....[<%08lx>] .. ( <= ",
+ task->preempt_trace_parent_eip[i]);
+ print_symbol("%s)\n", task->preempt_trace_parent_eip[i]);
+ }
+ printk("\n");
+}

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Next message: Shan Wei: "[PATCH]cfq: add the document of the tuning parameters"
Previous message: Lai Jiangshan: "Re: [PATCH] cpusets: fix deadlock with cpu_down()->cpuset_lock()"
Next in thread: Steven Rostedt: "Re: [PATCH][RT] stacktrace: dump out last preempt disablelocations"
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