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Date: Fri, 29 Sep 2006 13:20:57 -0700
From: Andrew Morton <akpm@...l.org>
To: Andi Kleen <ak@...e.de>
Cc: Ingo Molnar <mingo@...e.hu>, Badari Pulavarty <pbadari@...ibm.com>,
Jan Kara <jack@...e.cz>, torvalds@...l.org, stable@...nel.org,
ext4 <linux-ext4@...r.kernel.org>
Subject: Re: [patch 003/152] jbd: fix commit of ordered data buffers
On Fri, 29 Sep 2006 21:54:30 +0200
Andi Kleen <ak@...e.de> wrote:
> On Friday 29 September 2006 21:18, Ingo Molnar wrote:
> >
> > * Andrew Morton <akpm@...l.org> wrote:
> >
> > > gad, there have been so many all-CPU-backtrace patches over the years.
> > >
> > > <optimistically cc's Ingo>
> > >
> > > Ingo, do you think that's something which we shuld have in the
> > > spinlock debugging code? A trace to let us see which CPU is holding
> > > that lock, and where from? I guess if the other cpu is stuck in
> > > spin_lock_irqsave() then we'll get stuck delivering the IPI, so it'd
> > > need to be async.
> >
> > used to have this in -rt for i686 and x86_64 for the NMI watchdog tick
> > to print on all CPUs, in the next tick (i.e. no need to actually
> > initiate an IPI) - but it was all a bit hacky [but worked]. It fell
> > victim to some recent flux in that area.
>
> You mean spinlock debugging setting a global variable and the NMI
> watchdog testing that? Makes sense. I can put it on my todo list.
It does make sense.
<type, type>
Something like this? (compiled only)
From: Andrew Morton <akpm@...l.org>
When a spinlock lockup occurs, arrange for the NMI code to emit an all-cpu
backtrace, so we get to see which CPU is holding the lock, and where.
Cc: Andi Kleen <ak@....de>
Cc: Ingo Molnar <mingo@...e.hu>
Cc: Badari Pulavarty <pbadari@...ibm.com>
Signed-off-by: Andrew Morton <akpm@...l.org>
---
arch/i386/kernel/nmi.c | 14 ++++++++++++++
arch/x86_64/kernel/nmi.c | 17 ++++++++++++++++-
include/asm-i386/nmi.h | 3 +++
include/asm-x86_64/nmi.h | 3 +++
include/linux/nmi.h | 5 +++++
lib/spinlock_debug.c | 4 ++++
6 files changed, 45 insertions(+), 1 deletion(-)
diff -puN lib/spinlock_debug.c~spinlock-debug-all-cpu-backtrace lib/spinlock_debug.c
--- a/lib/spinlock_debug.c~spinlock-debug-all-cpu-backtrace
+++ a/lib/spinlock_debug.c
@@ -7,6 +7,7 @@
*/
#include <linux/spinlock.h>
+#include <linux/nmi.h>
#include <linux/interrupt.h>
#include <linux/debug_locks.h>
#include <linux/delay.h>
@@ -116,6 +117,9 @@ static void __spin_lock_debug(spinlock_t
raw_smp_processor_id(), current->comm,
current->pid, lock);
dump_stack();
+#ifdef CONFIG_SMP
+ trigger_all_cpu_backtrace();
+#endif
}
}
}
diff -puN arch/i386/kernel/nmi.c~spinlock-debug-all-cpu-backtrace arch/i386/kernel/nmi.c
--- a/arch/i386/kernel/nmi.c~spinlock-debug-all-cpu-backtrace
+++ a/arch/i386/kernel/nmi.c
@@ -23,6 +23,7 @@
#include <linux/percpu.h>
#include <linux/dmi.h>
#include <linux/kprobes.h>
+#include <linux/cpumask.h>
#include <asm/smp.h>
#include <asm/nmi.h>
@@ -40,6 +41,8 @@
static DEFINE_PER_CPU(unsigned long, perfctr_nmi_owner);
static DEFINE_PER_CPU(unsigned long, evntsel_nmi_owner[3]);
+static cpumask_t backtrace_mask = CPU_MASK_NONE;
+
/* this number is calculated from Intel's MSR_P4_CRU_ESCR5 register and it's
* offset from MSR_P4_BSU_ESCR0. It will be the max for all platforms (for now)
*/
@@ -905,6 +908,12 @@ __kprobes int nmi_watchdog_tick(struct p
touched = 1;
}
+ if (cpu_isset(cpu, backtrace_mask)) {
+ cpu_clear(cpu, backtrace_mask);
+ printk("NMI backtrace for cpu %d\n", cpu);
+ dump_stack();
+ }
+
sum = per_cpu(irq_stat, cpu).apic_timer_irqs;
/* if the apic timer isn't firing, this cpu isn't doing much */
@@ -1031,6 +1040,11 @@ int proc_nmi_enabled(struct ctl_table *t
#endif
+void __trigger_all_cpu_backtrace(void)
+{
+ backtrace_mask = CPU_MASK_ALL;
+}
+
EXPORT_SYMBOL(nmi_active);
EXPORT_SYMBOL(nmi_watchdog);
EXPORT_SYMBOL(avail_to_resrv_perfctr_nmi);
diff -puN arch/x86_64/kernel/nmi.c~spinlock-debug-all-cpu-backtrace arch/x86_64/kernel/nmi.c
--- a/arch/x86_64/kernel/nmi.c~spinlock-debug-all-cpu-backtrace
+++ a/arch/x86_64/kernel/nmi.c
@@ -12,14 +12,15 @@
* Mikael Pettersson : PM converted to driver model. Disable/enable API.
*/
+#include <linux/nmi.h>
#include <linux/mm.h>
#include <linux/delay.h>
#include <linux/interrupt.h>
#include <linux/module.h>
#include <linux/sysdev.h>
-#include <linux/nmi.h>
#include <linux/sysctl.h>
#include <linux/kprobes.h>
+#include <linux/cpumask.h>
#include <asm/smp.h>
#include <asm/nmi.h>
@@ -37,6 +38,8 @@
static DEFINE_PER_CPU(unsigned, perfctr_nmi_owner);
static DEFINE_PER_CPU(unsigned, evntsel_nmi_owner[2]);
+static cpumask_t backtrace_mask = CPU_MASK_NONE;
+
/* this number is calculated from Intel's MSR_P4_CRU_ESCR5 register and it's
* offset from MSR_P4_BSU_ESCR0. It will be the max for all platforms (for now)
*/
@@ -778,6 +781,7 @@ int __kprobes nmi_watchdog_tick(struct p
{
int sum;
int touched = 0;
+ int cpu = smp_processor_id();
struct nmi_watchdog_ctlblk *wd = &__get_cpu_var(nmi_watchdog_ctlblk);
u64 dummy;
int rc=0;
@@ -795,6 +799,12 @@ int __kprobes nmi_watchdog_tick(struct p
touched = 1;
}
+ if (cpu_isset(cpu, backtrace_mask)) {
+ cpu_clear(cpu, backtrace_mask);
+ printk("NMI backtrace for cpu %d\n", cpu);
+ dump_stack();
+ }
+
#ifdef CONFIG_X86_MCE
/* Could check oops_in_progress here too, but it's safer
not too */
@@ -927,6 +937,11 @@ int proc_nmi_enabled(struct ctl_table *t
#endif
+void __trigger_all_cpu_backtrace(void)
+{
+ backtrace_mask = CPU_MASK_ALL;
+}
+
EXPORT_SYMBOL(nmi_active);
EXPORT_SYMBOL(nmi_watchdog);
EXPORT_SYMBOL(avail_to_resrv_perfctr_nmi);
diff -puN include/linux/nmi.h~spinlock-debug-all-cpu-backtrace include/linux/nmi.h
--- a/include/linux/nmi.h~spinlock-debug-all-cpu-backtrace
+++ a/include/linux/nmi.h
@@ -14,9 +14,14 @@
* disables interrupts for a long time. This call is stateless.
*/
#ifdef ARCH_HAS_NMI_WATCHDOG
+#include <asm/nmi.h>
extern void touch_nmi_watchdog(void);
#else
# define touch_nmi_watchdog() do { } while(0)
#endif
+#ifndef trigger_all_cpu_backtrace
+#define trigger_all_cpu_backtrace() do { } while (0)
+#endif
+
#endif
diff -puN include/asm-i386/nmi.h~spinlock-debug-all-cpu-backtrace include/asm-i386/nmi.h
--- a/include/asm-i386/nmi.h~spinlock-debug-all-cpu-backtrace
+++ a/include/asm-i386/nmi.h
@@ -36,4 +36,7 @@ extern unsigned int nmi_watchdog;
#define NMI_LOCAL_APIC 2
#define NMI_INVALID 3
+void __trigger_all_cpu_backtrace(void);
+#define trigger_all_cpu_backtrace() __trigger_all_cpu_backtrace()
+
#endif /* ASM_NMI_H */
diff -puN include/asm-x86_64/nmi.h~spinlock-debug-all-cpu-backtrace include/asm-x86_64/nmi.h
--- a/include/asm-x86_64/nmi.h~spinlock-debug-all-cpu-backtrace
+++ a/include/asm-x86_64/nmi.h
@@ -70,4 +70,7 @@ extern unsigned int nmi_watchdog;
#define NMI_LOCAL_APIC 2
#define NMI_INVALID 3
+void __trigger_all_cpu_backtrace(void);
+#define trigger_all_cpu_backtrace() __trigger_all_cpu_backtrace()
+
#endif /* ASM_NMI_H */
_
-
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