linux-kernel - [PATCH] x86, UV: make kdump avoid stack dumps

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Message-Id: <E1ObLvt-0005UZ-Va@eag09.americas.sgi.com>
Date:	Tue, 20 Jul 2010 18:09:05 -0500
From:	Cliff Wickman <cpw@....com>
To:	linux-kernel@...r.kernel.org
Cc:	mingo@...e.hu, hpa@...or.com
Subject: [PATCH] x86, UV: make kdump avoid stack dumps


This patch is the same as one sent Jun18 2010.  It doesn't seem to 
have been noticed.


UV NMI callback's should not write stack dumps when a kdump is to be written.

When invoking the crash kernel to write a dump, kdump_nmi_shootdown_cpus()
uses NMI's to get all the cpu's to save their register context and halt.

But the NMI interrupt handler runs a callback list.  This patch sets a flag
to prevent any of those callbacks from interfering with the halt of the cpu.

For UV, which currently has the only callback to which this is relevant, the
uv_handle_nmi() callback should not do dumping of stacks.

The 'in_crash_kexec' flag is defined as an extern in kdebug.h firstly
because x2apic_uv_x.c includes it.  Secondly because some future callback
might need the flag to know that it should not enter the debugger.
(Such a scenario was in fact present in the 2.6.32 kernel, SuSE distribution,
 where a call to kdb needed to be avoided.)

Diffed against 2.6.35

Signed-off-by: Cliff Wickman <cpw@....com>
---
 arch/x86/include/asm/kdebug.h      |    1 +
 arch/x86/kernel/apic/x2apic_uv_x.c |    4 ++++
 arch/x86/kernel/crash.c            |    3 +++
 3 files changed, 8 insertions(+)

Index: linux-2.6.35-rc3/arch/x86/kernel/apic/x2apic_uv_x.c
===================================================================
--- linux-2.6.35-rc3.orig/arch/x86/kernel/apic/x2apic_uv_x.c
+++ linux-2.6.35-rc3/arch/x86/kernel/apic/x2apic_uv_x.c
@@ -604,6 +604,10 @@ int uv_handle_nmi(struct notifier_block 
 {
 	if (reason != DIE_NMI_IPI)
 		return NOTIFY_OK;
+
+	if (in_crash_kexec)
+		/* do nothing if entering the crash kernel */
+		return NOTIFY_OK;
 	/*
 	 * Use a lock so only one cpu prints at a time
 	 * to prevent intermixed output.
Index: linux-2.6.35-rc3/arch/x86/kernel/crash.c
===================================================================
--- linux-2.6.35-rc3.orig/arch/x86/kernel/crash.c
+++ linux-2.6.35-rc3/arch/x86/kernel/crash.c
@@ -28,6 +28,8 @@
 #include <asm/reboot.h>
 #include <asm/virtext.h>
 
+int in_crash_kexec;
+
 #if defined(CONFIG_SMP) && defined(CONFIG_X86_LOCAL_APIC)
 
 static void kdump_nmi_callback(int cpu, struct die_args *args)
@@ -61,6 +63,7 @@ static void kdump_nmi_callback(int cpu, 
 
 static void kdump_nmi_shootdown_cpus(void)
 {
+	in_crash_kexec = 1;
 	nmi_shootdown_cpus(kdump_nmi_callback);
 
 	disable_local_APIC();
Index: linux-2.6.35-rc3/arch/x86/include/asm/kdebug.h
===================================================================
--- linux-2.6.35-rc3.orig/arch/x86/include/asm/kdebug.h
+++ linux-2.6.35-rc3/arch/x86/include/asm/kdebug.h
@@ -33,5 +33,6 @@ extern void __show_regs(struct pt_regs *
 extern void show_regs(struct pt_regs *regs);
 extern unsigned long oops_begin(void);
 extern void oops_end(unsigned long, struct pt_regs *, int signr);
+extern int in_crash_kexec;
 
 #endif /* _ASM_X86_KDEBUG_H */
--
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