From ebc41f20d77f6ad91f1f2d2af5147dc9bb6b5eea Mon Sep 17 00:00:00 2001
From: Hidehiro Kawai <hidehiro.kawai.ez@hitachi.com>
Date: Tue, 22 Mar 2016 14:27:17 -0700
Subject: panic: change nmi_panic from macro to function

Commit 1717f2096b54 ("panic, x86: Fix re-entrance problem due to panic
on NMI") and commit 58c5661f2144 ("panic, x86: Allow CPUs to save
registers even if looping in NMI context") introduced nmi_panic() which
prevents concurrent/recursive execution of panic().  It also saves
registers for the crash dump on x86.

However, there are some cases where NMI handlers still use panic().
This patch set partially replaces them with nmi_panic() in those cases.

Even this patchset is applied, some NMI or similar handlers (e.g.  MCE
handler) continue to use panic().  This is because I can't test them
well and actual problems won't happen.  For example, the possibility
that normal panic and panic on MCE happen simultaneously is very low.

This patch (of 3):

Convert nmi_panic() to a proper function and export it instead of
exporting internal implementation details to modules, for obvious
reasons.

Signed-off-by: Hidehiro Kawai <hidehiro.kawai.ez@hitachi.com>
Acked-by: Borislav Petkov <bp@suse.de>
Acked-by: Michal Nazarewicz <mina86@mina86.com>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Rasmus Villemoes <linux@rasmusvillemoes.dk>
Cc: Nicolas Iooss <nicolas.iooss_linux@m4x.org>
Cc: Javi Merino <javi.merino@arm.com>
Cc: Gobinda Charan Maji <gobinda.cemk07@gmail.com>
Cc: "Steven Rostedt (Red Hat)" <rostedt@goodmis.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Vitaly Kuznetsov <vkuznets@redhat.com>
Cc: HATAYAMA Daisuke <d.hatayama@jp.fujitsu.com>
Cc: Tejun Heo <tj@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
---
 kernel/panic.c | 20 ++++++++++++++++++++
 1 file changed, 20 insertions(+)

(limited to 'kernel/panic.c')

diff --git a/kernel/panic.c b/kernel/panic.c
index fa400852bf6c..535c96510a44 100644
--- a/kernel/panic.c
+++ b/kernel/panic.c
@@ -73,6 +73,26 @@ void __weak nmi_panic_self_stop(struct pt_regs *regs)
 
 atomic_t panic_cpu = ATOMIC_INIT(PANIC_CPU_INVALID);
 
+/*
+ * A variant of panic() called from NMI context. We return if we've already
+ * panicked on this CPU. If another CPU already panicked, loop in
+ * nmi_panic_self_stop() which can provide architecture dependent code such
+ * as saving register state for crash dump.
+ */
+void nmi_panic(struct pt_regs *regs, const char *msg)
+{
+	int old_cpu, cpu;
+
+	cpu = raw_smp_processor_id();
+	old_cpu = atomic_cmpxchg(&panic_cpu, PANIC_CPU_INVALID, cpu);
+
+	if (old_cpu == PANIC_CPU_INVALID)
+		panic("%s", msg);
+	else if (old_cpu != cpu)
+		nmi_panic_self_stop(regs);
+}
+EXPORT_SYMBOL(nmi_panic);
+
 /**
  *	panic - halt the system
  *	@fmt: The text string to print
-- 
cgit