[tip:x86/urgent] x86: Fix trigger_all_cpu_backtrace() implementation

From: tip-bot for Michel Lespinasse
Date: Thu Jun 20 2013 - 10:48:57 EST

Commit-ID: b52e0a7c4e4100f8683af508664e60e1603070f9
Gitweb: http://git.kernel.org/tip/b52e0a7c4e4100f8683af508664e60e1603070f9
Author: Michel Lespinasse <walken@xxxxxxxxxx>
AuthorDate: Thu, 6 Jun 2013 04:41:15 -0700
Committer: Ingo Molnar <mingo@xxxxxxxxxx>
CommitDate: Thu, 20 Jun 2013 14:00:21 +0200

x86: Fix trigger_all_cpu_backtrace() implementation

The following change fixes the x86 implementation of
trigger_all_cpu_backtrace(), which was previously (accidentally,
as far as I can tell) disabled to always return false as on
architectures that do not implement this function.

trigger_all_cpu_backtrace(), as defined in include/linux/nmi.h,
should call arch_trigger_all_cpu_backtrace() if available, or
return false if the underlying arch doesn't implement this

x86 did provide a suitable arch_trigger_all_cpu_backtrace()
implementation, but it wasn't actually being used because it was
declared in asm/nmi.h, which linux/nmi.h doesn't include. Also,
linux/nmi.h couldn't easily be fixed by including asm/nmi.h,
because that file is not available on all architectures.

I am proposing to fix this by moving the x86 definition of
arch_trigger_all_cpu_backtrace() to asm/irq.h.

Tested via: echo l > /proc/sysrq-trigger

Before the change, this uses a fallback implementation which
shows backtraces on active CPUs (using
smp_call_function_interrupt() )

After the change, this shows NMI backtraces on all CPUs

Signed-off-by: Michel Lespinasse <walken@xxxxxxxxxx>
Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Link: http://lkml.kernel.org/r/1370518875-1346-1-git-send-email-walken@xxxxxxxxxx
Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx>
arch/x86/include/asm/irq.h | 5 +++++
arch/x86/include/asm/nmi.h | 4 +---
arch/x86/kernel/apic/hw_nmi.c | 1 +
3 files changed, 7 insertions(+), 3 deletions(-)

diff --git a/arch/x86/include/asm/irq.h b/arch/x86/include/asm/irq.h
index ba870bb..57873be 100644
--- a/arch/x86/include/asm/irq.h
+++ b/arch/x86/include/asm/irq.h
@@ -41,4 +41,9 @@ extern int vector_used_by_percpu_irq(unsigned int vector);

extern void init_ISA_irqs(void);

+void arch_trigger_all_cpu_backtrace(void);
+#define arch_trigger_all_cpu_backtrace arch_trigger_all_cpu_backtrace
#endif /* _ASM_X86_IRQ_H */
diff --git a/arch/x86/include/asm/nmi.h b/arch/x86/include/asm/nmi.h
index c0fa356..86f9301 100644
--- a/arch/x86/include/asm/nmi.h
+++ b/arch/x86/include/asm/nmi.h
@@ -18,9 +18,7 @@ extern int proc_nmi_enabled(struct ctl_table *, int ,
void __user *, size_t *, loff_t *);
extern int unknown_nmi_panic;

-void arch_trigger_all_cpu_backtrace(void);
-#define arch_trigger_all_cpu_backtrace arch_trigger_all_cpu_backtrace
+#endif /* CONFIG_X86_LOCAL_APIC */

#define NMI_FLAG_FIRST 1

diff --git a/arch/x86/kernel/apic/hw_nmi.c b/arch/x86/kernel/apic/hw_nmi.c
index 31cb9ae..a698d71 100644
--- a/arch/x86/kernel/apic/hw_nmi.c
+++ b/arch/x86/kernel/apic/hw_nmi.c
@@ -9,6 +9,7 @@
#include <asm/apic.h>
+#include <asm/nmi.h>

#include <linux/cpumask.h>
#include <linux/kdebug.h>
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