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Subject[V3 PATCH] x86: avoid calling arch_trigger_all_cpu_backtrace() at the same time on SMP
Date
The spin_lock_debug/rcu_cpu_stall detector uses
trigger_all_cpu_backtrace() to dump cpu backtrace.
Therefore it is possible that trigger_all_cpu_backtrace()
could be called at the same time on different CPUs, which
triggers and 'unknown reason NMI' warning. The following case
illustrates the problem:

CPU1 CPU2 ... CPU N
trigger_all_cpu_backtrace()
set "backtrace_mask" to cpu mask
|
generate NMI interrupts generate NMI interrupts ...
\ | /
\ | /
The "backtrace_mask" will be cleaned by the first NMI interrupt
at nmi_watchdog_tick(), then the following NMI interrupts generated
by other cpus's arch_trigger_all_cpu_backtrace() will be took as
unknown reason NMI interrupts.
This patch uses a lock to avoid the problem, and stop the
arch_trigger_all_cpu_backtrace() calling to avoid dumping double cpu
backtrace info when there is already a trigger_all_cpu_backtrace()
in progress.

Signed-off-by: Dongdong Deng <dongdong.deng@windriver.com>
Reviewed-by: Bruce Ashfield <bruce.ashfield@windriver.com>
CC: Thomas Gleixner <tglx@linutronix.de>
CC: Ingo Molnar <mingo@redhat.com>
CC: "H. Peter Anvin" <hpa@zytor.com>
CC: x86@kernel.org
CC: linux-kernel@vger.kernel.org
Signed-off-by: Don Zickus <dzickus@redhat.com>
---
arch/x86/kernel/apic/hw_nmi.c | 23 +++++++++++++++++++++++
arch/x86/kernel/apic/nmi.c | 23 +++++++++++++++++++++++
2 files changed, 46 insertions(+), 0 deletions(-)
diff --git a/arch/x86/kernel/apic/hw_nmi.c b/arch/x86/kernel/apic/hw_nmi.c
index cefd694..bfdab3b 100644
--- a/arch/x86/kernel/apic/hw_nmi.c
+++ b/arch/x86/kernel/apic/hw_nmi.c
@@ -26,9 +26,27 @@ u64 hw_nmi_get_sample_period(void)
}

#ifdef ARCH_HAS_NMI_WATCHDOG
+/* "in progress" flag of arch_trigger_all_cpu_backtrace */
+static unsigned long backtrace_flag;
+
void arch_trigger_all_cpu_backtrace(void)
{
int i;
+ unsigned long flags;
+
+ /*
+ * Have to disable irq here, as the
+ * arch_trigger_all_cpu_backtrace() could be
+ * triggered by "spin_lock()" with irqs on.
+ */
+ local_irq_save(flags);
+
+ if (test_and_set_bit(0, &backtrace_flag))
+ /*
+ * If there is already a trigger_all_cpu_backtrace() in progress
+ * (backtrace_flag == 1), don't output double cpu dump infos.
+ */
+ goto out_restore_irq;

cpumask_copy(to_cpumask(backtrace_mask), cpu_online_mask);

@@ -41,6 +59,11 @@ void arch_trigger_all_cpu_backtrace(void)
break;
mdelay(1);
}
+
+ clear_bit(0, &backtrace_flag);
+
+out_restore_irq:
+ local_irq_restore(flags);
}

static int __kprobes
diff --git a/arch/x86/kernel/apic/nmi.c b/arch/x86/kernel/apic/nmi.c
index c90041c..bd9cb79 100644
--- a/arch/x86/kernel/apic/nmi.c
+++ b/arch/x86/kernel/apic/nmi.c
@@ -549,9 +549,27 @@ int do_nmi_callback(struct pt_regs *regs, int cpu)
return 0;
}

+/* "in progress" flag of arch_trigger_all_cpu_backtrace */
+static unsigned long backtrace_flag;
+
void arch_trigger_all_cpu_backtrace(void)
{
int i;
+ unsigned long flags;
+
+ /*
+ * Have to disable irq here, as the
+ * arch_trigger_all_cpu_backtrace() could be
+ * triggered by "spin_lock()" with irqs on.
+ */
+ local_irq_save(flags);
+
+ if (test_and_set_bit(0, &backtrace_flag))
+ /*
+ * If there is already a trigger_all_cpu_backtrace() in progress
+ * (backtrace_flag == 1), don't output double cpu dump infos.
+ */
+ goto out_restore_irq;

cpumask_copy(to_cpumask(backtrace_mask), cpu_online_mask);

@@ -564,4 +582,9 @@ void arch_trigger_all_cpu_backtrace(void)
break;
mdelay(1);
}
+
+ clear_bit(0, &backtrace_flag);
+
+out_restore_irq:
+ local_irq_restore(flags);
}
--
1.6.0.4


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