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Date: Mon, 09 Aug 2010 16:11:22 -0500 From: Cliff Wickman <cpw@....com> To: linux-kernel@...r.kernel.org Cc: mingo@...e.hu, hpa@...or.com Subject: [PATCH v2] x86, UV: make kdump avoid stack dumps This replaces Version 1 of this patch, which broke the build when CONFIG_KEXEC and CONFIG_CRASH_DUMP were configured off. In that case the storage for the 'in_crash_kexec' flag was never built. This v2 was submitted on 7/22, but apparently never seen (probably too close in date and name to v1, sent on 7/20). This version defines that flag as 0 if CONFIG_KEXEC is not set. The patch is tested with all combinations of those two options. 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 | 6 ++++++ arch/x86/kernel/apic/x2apic_uv_x.c | 4 ++++ arch/x86/kernel/crash.c | 3 +++ 3 files changed, 13 insertions(+) Index: 100722.linux-tip/arch/x86/kernel/apic/x2apic_uv_x.c =================================================================== --- 100722.linux-tip.orig/arch/x86/kernel/apic/x2apic_uv_x.c +++ 100722.linux-tip/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: 100722.linux-tip/arch/x86/kernel/crash.c =================================================================== --- 100722.linux-tip.orig/arch/x86/kernel/crash.c +++ 100722.linux-tip/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: 100722.linux-tip/arch/x86/include/asm/kdebug.h =================================================================== --- 100722.linux-tip.orig/arch/x86/include/asm/kdebug.h +++ 100722.linux-tip/arch/x86/include/asm/kdebug.h @@ -33,5 +33,11 @@ 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); +#ifdef CONFIG_KEXEC +extern int in_crash_kexec; +#else +/* no crash dump is ever in progress if no crash kernel can be kexec'd */ +#define in_crash_kexec 0 +#endif #endif /* _ASM_X86_KDEBUG_H */ -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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