From: Nicholas Piggin <npiggin@xxxxxxxxx> Subject: powerpc/64s: implement arch-specific hardlockup watchdog Implement an arch-speicfic watchdog rather than use the perf-based hardlockup detector. The new watchdog takes the soft-NMI directly, rather than going through perf. Perf interrupts are to be made maskable in future, so that would prevent the perf detector from working in those regions. Additionally, implement a SMP based detector where all CPUs watch one another by pinging a shared cpumask. This is because powerpc Book3S does not have a true periodic local NMI, but some platforms do implement a true NMI IPI. If a CPU is stuck with interrupts hard disabled, the soft-NMI watchdog does not work, but the SMP watchdog will. Even on platforms without a true NMI IPI to get a good trace from the stuck CPU, other CPUs will notice the lockup sufficiently to report it and panic. [npiggin@xxxxxxxxx: honor watchdog disable at boot/hotplug] Link: http://lkml.kernel.org/r/20170621001346.5bb337c9@xxxxxxxxxxxxxxxxxxx [npiggin@xxxxxxxxx: fix false positive warning at CPU unplug] Link: http://lkml.kernel.org/r/20170630080740.20766-1-npiggin@xxxxxxxxx [akpm@xxxxxxxxxxxxxxxxxxxx: coding-style fixes] Link: http://lkml.kernel.org/r/20170616065715.18390-6-npiggin@xxxxxxxxx Signed-off-by: Nicholas Piggin <npiggin@xxxxxxxxx> Reviewed-by: Don Zickus <dzickus@xxxxxxxxxx> Tested-by: Babu Moger <babu.moger@xxxxxxxxxx> [sparc] Cc: Benjamin Herrenschmidt <benh@xxxxxxxxxxxxxxxxxxx> Cc: Paul Mackerras <paulus@xxxxxxxxx> Cc: Michael Ellerman <mpe@xxxxxxxxxxxxxx> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> --- arch/powerpc/Kconfig | 7 arch/powerpc/include/asm/nmi.h | 11 arch/powerpc/include/asm/smp.h | 2 arch/powerpc/kernel/Makefile | 1 arch/powerpc/kernel/exceptions-64s.S | 30 + arch/powerpc/kernel/kvm.c | 7 arch/powerpc/kernel/setup_64.c | 19 - arch/powerpc/kernel/smp.c | 20 + arch/powerpc/kernel/watchdog.c | 386 +++++++++++++++++++++++++ 9 files changed, 458 insertions(+), 25 deletions(-) diff -puN arch/powerpc/Kconfig~powerpc-64s-implement-arch-specific-hardlockup-watchdog arch/powerpc/Kconfig --- a/arch/powerpc/Kconfig~powerpc-64s-implement-arch-specific-hardlockup-watchdog +++ a/arch/powerpc/Kconfig @@ -82,7 +82,7 @@ config NR_IRQS config NMI_IPI bool - depends on SMP && (DEBUGGER || KEXEC_CORE) + depends on SMP && (DEBUGGER || KEXEC_CORE || HARDLOCKUP_DETECTOR) default y config STACKTRACE_SUPPORT @@ -192,12 +192,13 @@ config PPC select HAVE_MEMBLOCK select HAVE_MEMBLOCK_NODE_MAP select HAVE_MOD_ARCH_SPECIFIC - select HAVE_NMI if PERF_EVENTS + select HAVE_NMI if PERF_EVENTS || (PPC64 && PPC_BOOK3S) + select HAVE_HARDLOCKUP_DETECTOR_ARCH if (PPC64 && PPC_BOOK3S) select HAVE_OPROFILE select HAVE_OPTPROBES if PPC64 select HAVE_PERF_EVENTS select HAVE_PERF_EVENTS_NMI if PPC64 - select HAVE_HARDLOCKUP_DETECTOR_PERF if HAVE_PERF_EVENTS_NMI + select HAVE_HARDLOCKUP_DETECTOR_PERF if HAVE_PERF_EVENTS_NMI && !HAVE_HARDLOCKUP_DETECTOR_ARCH select HAVE_PERF_REGS select HAVE_PERF_USER_STACK_DUMP select HAVE_RCU_TABLE_FREE if SMP diff -puN arch/powerpc/include/asm/nmi.h~powerpc-64s-implement-arch-specific-hardlockup-watchdog arch/powerpc/include/asm/nmi.h --- a/arch/powerpc/include/asm/nmi.h~powerpc-64s-implement-arch-specific-hardlockup-watchdog +++ a/arch/powerpc/include/asm/nmi.h @@ -1,4 +1,15 @@ #ifndef _ASM_NMI_H #define _ASM_NMI_H +#ifdef CONFIG_HARDLOCKUP_DETECTOR +extern void arch_touch_nmi_watchdog(void); + +extern void arch_trigger_cpumask_backtrace(const cpumask_t *mask, + bool exclude_self); +#define arch_trigger_cpumask_backtrace arch_trigger_cpumask_backtrace + +#else +static inline void arch_touch_nmi_watchdog(void) {} +#endif + #endif /* _ASM_NMI_H */ diff -puN arch/powerpc/include/asm/smp.h~powerpc-64s-implement-arch-specific-hardlockup-watchdog arch/powerpc/include/asm/smp.h --- a/arch/powerpc/include/asm/smp.h~powerpc-64s-implement-arch-specific-hardlockup-watchdog +++ a/arch/powerpc/include/asm/smp.h @@ -55,6 +55,8 @@ struct smp_ops_t { int (*cpu_bootable)(unsigned int nr); }; +extern void smp_flush_nmi_ipi(u64 delay_us); +extern int smp_send_nmi_ipi(int cpu, void (*fn)(struct pt_regs *), u64 delay_us); extern void smp_send_debugger_break(void); extern void start_secondary_resume(void); extern void smp_generic_give_timebase(void); diff -puN arch/powerpc/kernel/Makefile~powerpc-64s-implement-arch-specific-hardlockup-watchdog arch/powerpc/kernel/Makefile --- a/arch/powerpc/kernel/Makefile~powerpc-64s-implement-arch-specific-hardlockup-watchdog +++ a/arch/powerpc/kernel/Makefile @@ -38,6 +38,7 @@ obj-$(CONFIG_PPC64) += setup_64.o sys_p signal_64.o ptrace32.o \ paca.o nvram_64.o firmware.o obj-$(CONFIG_VDSO32) += vdso32/ +obj-$(CONFIG_HARDLOCKUP_DETECTOR) += watchdog.o obj-$(CONFIG_HAVE_HW_BREAKPOINT) += hw_breakpoint.o obj-$(CONFIG_PPC_BOOK3S_64) += cpu_setup_ppc970.o cpu_setup_pa6t.o obj-$(CONFIG_PPC_BOOK3S_64) += cpu_setup_power.o diff -puN arch/powerpc/kernel/exceptions-64s.S~powerpc-64s-implement-arch-specific-hardlockup-watchdog arch/powerpc/kernel/exceptions-64s.S --- a/arch/powerpc/kernel/exceptions-64s.S~powerpc-64s-implement-arch-specific-hardlockup-watchdog +++ a/arch/powerpc/kernel/exceptions-64s.S @@ -1314,6 +1314,31 @@ EXC_REAL_NONE(0x1800, 0x100) EXC_VIRT_NONE(0x5800, 0x100) #endif +#if defined(CONFIG_HARDLOCKUP_DETECTOR) && defined(CONFIG_HAVE_HARDLOCKUP_DETECTOR_ARCH) + +#define MASKED_DEC_HANDLER_LABEL 3f + +#define MASKED_DEC_HANDLER(_H) \ +3: /* soft-nmi */ \ + std r12,PACA_EXGEN+EX_R12(r13); \ + GET_SCRATCH0(r10); \ + std r10,PACA_EXGEN+EX_R13(r13); \ + EXCEPTION_PROLOG_PSERIES_1(soft_nmi_common, _H) + +EXC_COMMON_BEGIN(soft_nmi_common) + mr r10,r1 + ld r1,PACAEMERGSP(r13) + ld r1,PACA_NMI_EMERG_SP(r13) + subi r1,r1,INT_FRAME_SIZE + EXCEPTION_COMMON_NORET_STACK(PACA_EXGEN, 0x900, + system_reset, soft_nmi_interrupt, + ADD_NVGPRS;ADD_RECONCILE) + b ret_from_except + +#else +#define MASKED_DEC_HANDLER_LABEL 2f /* normal return */ +#define MASKED_DEC_HANDLER(_H) +#endif /* * An interrupt came in while soft-disabled. We set paca->irq_happened, then: @@ -1336,7 +1361,7 @@ masked_##_H##interrupt: \ lis r10,0x7fff; \ ori r10,r10,0xffff; \ mtspr SPRN_DEC,r10; \ - b 2f; \ + b MASKED_DEC_HANDLER_LABEL; \ 1: cmpwi r10,PACA_IRQ_DBELL; \ beq 2f; \ cmpwi r10,PACA_IRQ_HMI; \ @@ -1351,7 +1376,8 @@ masked_##_H##interrupt: \ ld r11,PACA_EXGEN+EX_R11(r13); \ GET_SCRATCH0(r13); \ ##_H##rfid; \ - b . + b .; \ + MASKED_DEC_HANDLER(_H) /* * Real mode exceptions actually use this too, but alternate diff -puN arch/powerpc/kernel/kvm.c~powerpc-64s-implement-arch-specific-hardlockup-watchdog arch/powerpc/kernel/kvm.c --- a/arch/powerpc/kernel/kvm.c~powerpc-64s-implement-arch-specific-hardlockup-watchdog +++ a/arch/powerpc/kernel/kvm.c @@ -25,6 +25,7 @@ #include <linux/kvm_para.h> #include <linux/slab.h> #include <linux/of.h> +#include <linux/nmi.h> /* hardlockup_detector_disable() */ #include <asm/reg.h> #include <asm/sections.h> @@ -718,6 +719,12 @@ static __init void kvm_free_tmp(void) static int __init kvm_guest_init(void) { + /* + * The hardlockup detector is likely to get false positives in + * KVM guests, so disable it by default. + */ + hardlockup_detector_disable(); + if (!kvm_para_available()) goto free_tmp; diff -puN arch/powerpc/kernel/setup_64.c~powerpc-64s-implement-arch-specific-hardlockup-watchdog arch/powerpc/kernel/setup_64.c --- a/arch/powerpc/kernel/setup_64.c~powerpc-64s-implement-arch-specific-hardlockup-watchdog +++ a/arch/powerpc/kernel/setup_64.c @@ -751,22 +751,3 @@ unsigned long memory_block_size_bytes(vo struct ppc_pci_io ppc_pci_io; EXPORT_SYMBOL(ppc_pci_io); #endif - -#ifdef CONFIG_HARDLOCKUP_DETECTOR_PERF -u64 hw_nmi_get_sample_period(int watchdog_thresh) -{ - return ppc_proc_freq * watchdog_thresh; -} - -/* - * The hardlockup detector breaks PMU event based branches and is likely - * to get false positives in KVM guests, so disable it by default. - */ -static int __init disable_hardlockup_detector(void) -{ - hardlockup_detector_disable(); - - return 0; -} -early_initcall(disable_hardlockup_detector); -#endif diff -puN arch/powerpc/kernel/smp.c~powerpc-64s-implement-arch-specific-hardlockup-watchdog arch/powerpc/kernel/smp.c --- a/arch/powerpc/kernel/smp.c~powerpc-64s-implement-arch-specific-hardlockup-watchdog +++ a/arch/powerpc/kernel/smp.c @@ -435,13 +435,31 @@ static void do_smp_send_nmi_ipi(int cpu) } } +void smp_flush_nmi_ipi(u64 delay_us) +{ + unsigned long flags; + + nmi_ipi_lock_start(&flags); + while (nmi_ipi_busy_count) { + nmi_ipi_unlock_end(&flags); + udelay(1); + if (delay_us) { + delay_us--; + if (!delay_us) + return; + } + nmi_ipi_lock_start(&flags); + } + nmi_ipi_unlock_end(&flags); +} + /* * - cpu is the target CPU (must not be this CPU), or NMI_IPI_ALL_OTHERS. * - fn is the target callback function. * - delay_us > 0 is the delay before giving up waiting for targets to * enter the handler, == 0 specifies indefinite delay. */ -static int smp_send_nmi_ipi(int cpu, void (*fn)(struct pt_regs *), u64 delay_us) +int smp_send_nmi_ipi(int cpu, void (*fn)(struct pt_regs *), u64 delay_us) { unsigned long flags; int me = raw_smp_processor_id(); diff -puN /dev/null arch/powerpc/kernel/watchdog.c --- /dev/null +++ a/arch/powerpc/kernel/watchdog.c @@ -0,0 +1,386 @@ +/* + * Watchdog support on powerpc systems. + * + * Copyright 2017, IBM Corporation. + * + * This uses code from arch/sparc/kernel/nmi.c and kernel/watchdog.c + */ +#include <linux/kernel.h> +#include <linux/param.h> +#include <linux/init.h> +#include <linux/percpu.h> +#include <linux/cpu.h> +#include <linux/nmi.h> +#include <linux/module.h> +#include <linux/export.h> +#include <linux/kprobes.h> +#include <linux/hardirq.h> +#include <linux/reboot.h> +#include <linux/slab.h> +#include <linux/kdebug.h> +#include <linux/sched/debug.h> +#include <linux/delay.h> +#include <linux/smp.h> + +#include <asm/paca.h> + +/* + * The watchdog has a simple timer that runs on each CPU, once per timer + * period. This is the heartbeat. + * + * Then there are checks to see if the heartbeat has not triggered on a CPU + * for the panic timeout period. Currently the watchdog only supports an + * SMP check, so the heartbeat only turns on when we have 2 or more CPUs. + * + * This is not an NMI watchdog, but Linux uses that name for a generic + * watchdog in some cases, so NMI gets used in some places. + */ + +static cpumask_t wd_cpus_enabled __read_mostly; + +static u64 wd_panic_timeout_tb __read_mostly; /* timebase ticks until panic */ +static u64 wd_smp_panic_timeout_tb __read_mostly; /* panic other CPUs */ + +static u64 wd_timer_period_ms __read_mostly; /* interval between heartbeat */ + +static DEFINE_PER_CPU(struct timer_list, wd_timer); +static DEFINE_PER_CPU(u64, wd_timer_tb); + +/* + * These are for the SMP checker. CPUs clear their pending bit in their + * heartbeat. If the bitmask becomes empty, the time is noted and the + * bitmask is refilled. + * + * All CPUs clear their bit in the pending mask every timer period. + * Once all have cleared, the time is noted and the bits are reset. + * If the time since all clear was greater than the panic timeout, + * we can panic with the list of stuck CPUs. + * + * This will work best with NMI IPIs for crash code so the stuck CPUs + * can be pulled out to get their backtraces. + */ +static unsigned long __wd_smp_lock; +static cpumask_t wd_smp_cpus_pending; +static cpumask_t wd_smp_cpus_stuck; +static u64 wd_smp_last_reset_tb; + +static inline void wd_smp_lock(unsigned long *flags) +{ + /* + * Avoid locking layers if possible. + * This may be called from low level interrupt handlers at some + * point in future. + */ + local_irq_save(*flags); + while (unlikely(test_and_set_bit_lock(0, &__wd_smp_lock))) + cpu_relax(); +} + +static inline void wd_smp_unlock(unsigned long *flags) +{ + clear_bit_unlock(0, &__wd_smp_lock); + local_irq_restore(*flags); +} + +static void wd_lockup_ipi(struct pt_regs *regs) +{ + pr_emerg("Watchdog CPU:%d Hard LOCKUP\n", raw_smp_processor_id()); + print_modules(); + print_irqtrace_events(current); + if (regs) + show_regs(regs); + else + dump_stack(); + + if (hardlockup_panic) + nmi_panic(regs, "Hard LOCKUP"); +} + +static void set_cpu_stuck(int cpu, u64 tb) +{ + cpumask_set_cpu(cpu, &wd_smp_cpus_stuck); + cpumask_clear_cpu(cpu, &wd_smp_cpus_pending); + if (cpumask_empty(&wd_smp_cpus_pending)) { + wd_smp_last_reset_tb = tb; + cpumask_andnot(&wd_smp_cpus_pending, + &wd_cpus_enabled, + &wd_smp_cpus_stuck); + } +} + +static void watchdog_smp_panic(int cpu, u64 tb) +{ + unsigned long flags; + int c; + + wd_smp_lock(&flags); + /* Double check some things under lock */ + if ((s64)(tb - wd_smp_last_reset_tb) < (s64)wd_smp_panic_timeout_tb) + goto out; + if (cpumask_test_cpu(cpu, &wd_smp_cpus_pending)) + goto out; + if (cpumask_weight(&wd_smp_cpus_pending) == 0) + goto out; + + pr_emerg("Watchdog CPU:%d detected Hard LOCKUP other CPUS:%*pbl\n", + cpu, cpumask_pr_args(&wd_smp_cpus_pending)); + + /* + * Try to trigger the stuck CPUs. + */ + for_each_cpu(c, &wd_smp_cpus_pending) { + if (c == cpu) + continue; + smp_send_nmi_ipi(c, wd_lockup_ipi, 1000000); + } + smp_flush_nmi_ipi(1000000); + + /* Take the stuck CPU out of the watch group */ + for_each_cpu(c, &wd_smp_cpus_pending) + set_cpu_stuck(c, tb); + +out: + wd_smp_unlock(&flags); + + printk_safe_flush(); + /* + * printk_safe_flush() seems to require another print + * before anything actually goes out to console. + */ + if (sysctl_hardlockup_all_cpu_backtrace) + trigger_allbutself_cpu_backtrace(); + + if (hardlockup_panic) + nmi_panic(NULL, "Hard LOCKUP"); +} + +static void wd_smp_clear_cpu_pending(int cpu, u64 tb) +{ + if (!cpumask_test_cpu(cpu, &wd_smp_cpus_pending)) { + if (unlikely(cpumask_test_cpu(cpu, &wd_smp_cpus_stuck))) { + unsigned long flags; + + pr_emerg("Watchdog CPU:%d became unstuck\n", cpu); + wd_smp_lock(&flags); + cpumask_clear_cpu(cpu, &wd_smp_cpus_stuck); + wd_smp_unlock(&flags); + } + return; + } + cpumask_clear_cpu(cpu, &wd_smp_cpus_pending); + if (cpumask_empty(&wd_smp_cpus_pending)) { + unsigned long flags; + + wd_smp_lock(&flags); + if (cpumask_empty(&wd_smp_cpus_pending)) { + wd_smp_last_reset_tb = tb; + cpumask_andnot(&wd_smp_cpus_pending, + &wd_cpus_enabled, + &wd_smp_cpus_stuck); + } + wd_smp_unlock(&flags); + } +} + +static void watchdog_timer_interrupt(int cpu) +{ + u64 tb = get_tb(); + + per_cpu(wd_timer_tb, cpu) = tb; + + wd_smp_clear_cpu_pending(cpu, tb); + + if ((s64)(tb - wd_smp_last_reset_tb) >= (s64)wd_smp_panic_timeout_tb) + watchdog_smp_panic(cpu, tb); +} + +void soft_nmi_interrupt(struct pt_regs *regs) +{ + unsigned long flags; + int cpu = raw_smp_processor_id(); + u64 tb; + + if (!cpumask_test_cpu(cpu, &wd_cpus_enabled)) + return; + + nmi_enter(); + tb = get_tb(); + if (tb - per_cpu(wd_timer_tb, cpu) >= wd_panic_timeout_tb) { + per_cpu(wd_timer_tb, cpu) = tb; + + wd_smp_lock(&flags); + if (cpumask_test_cpu(cpu, &wd_smp_cpus_stuck)) { + wd_smp_unlock(&flags); + goto out; + } + set_cpu_stuck(cpu, tb); + + pr_emerg("Watchdog CPU:%d Hard LOCKUP\n", cpu); + print_modules(); + print_irqtrace_events(current); + if (regs) + show_regs(regs); + else + dump_stack(); + + wd_smp_unlock(&flags); + + if (sysctl_hardlockup_all_cpu_backtrace) + trigger_allbutself_cpu_backtrace(); + + if (hardlockup_panic) + nmi_panic(regs, "Hard LOCKUP"); + } + if (wd_panic_timeout_tb < 0x7fffffff) + mtspr(SPRN_DEC, wd_panic_timeout_tb); + +out: + nmi_exit(); +} + +static void wd_timer_reset(unsigned int cpu, struct timer_list *t) +{ + t->expires = jiffies + msecs_to_jiffies(wd_timer_period_ms); + if (wd_timer_period_ms > 1000) + t->expires = __round_jiffies_up(t->expires, cpu); + add_timer_on(t, cpu); +} + +static void wd_timer_fn(unsigned long data) +{ + struct timer_list *t = this_cpu_ptr(&wd_timer); + int cpu = smp_processor_id(); + + watchdog_timer_interrupt(cpu); + + wd_timer_reset(cpu, t); +} + +void arch_touch_nmi_watchdog(void) +{ + int cpu = smp_processor_id(); + + watchdog_timer_interrupt(cpu); +} +EXPORT_SYMBOL(arch_touch_nmi_watchdog); + +static void start_watchdog_timer_on(unsigned int cpu) +{ + struct timer_list *t = per_cpu_ptr(&wd_timer, cpu); + + per_cpu(wd_timer_tb, cpu) = get_tb(); + + setup_pinned_timer(t, wd_timer_fn, 0); + wd_timer_reset(cpu, t); +} + +static void stop_watchdog_timer_on(unsigned int cpu) +{ + struct timer_list *t = per_cpu_ptr(&wd_timer, cpu); + + del_timer_sync(t); +} + +static int start_wd_on_cpu(unsigned int cpu) +{ + if (cpumask_test_cpu(cpu, &wd_cpus_enabled)) { + WARN_ON(1); + return 0; + } + + if (!(watchdog_enabled & NMI_WATCHDOG_ENABLED)) + return 0; + + if (watchdog_suspended) + return 0; + + if (!cpumask_test_cpu(cpu, &watchdog_cpumask)) + return 0; + + cpumask_set_cpu(cpu, &wd_cpus_enabled); + if (cpumask_weight(&wd_cpus_enabled) == 1) { + cpumask_set_cpu(cpu, &wd_smp_cpus_pending); + wd_smp_last_reset_tb = get_tb(); + } + smp_wmb(); + start_watchdog_timer_on(cpu); + + return 0; +} + +static int stop_wd_on_cpu(unsigned int cpu) +{ + if (!cpumask_test_cpu(cpu, &wd_cpus_enabled)) + return 0; /* Can happen in CPU unplug case */ + + stop_watchdog_timer_on(cpu); + + cpumask_clear_cpu(cpu, &wd_cpus_enabled); + wd_smp_clear_cpu_pending(cpu, get_tb()); + + return 0; +} + +static void watchdog_calc_timeouts(void) +{ + wd_panic_timeout_tb = watchdog_thresh * ppc_tb_freq; + + /* Have the SMP detector trigger a bit later */ + wd_smp_panic_timeout_tb = wd_panic_timeout_tb * 3 / 2; + + /* 2/5 is the factor that the perf based detector uses */ + wd_timer_period_ms = watchdog_thresh * 1000 * 2 / 5; +} + +void watchdog_nmi_reconfigure(void) +{ + int cpu; + + watchdog_calc_timeouts(); + + for_each_cpu(cpu, &wd_cpus_enabled) + stop_wd_on_cpu(cpu); + + for_each_cpu_and(cpu, cpu_online_mask, &watchdog_cpumask) + start_wd_on_cpu(cpu); +} + +/* + * This runs after lockup_detector_init() which sets up watchdog_cpumask. + */ +static int __init powerpc_watchdog_init(void) +{ + int err; + + watchdog_calc_timeouts(); + + err = cpuhp_setup_state(CPUHP_AP_ONLINE_DYN, "powerpc/watchdog:online", + start_wd_on_cpu, stop_wd_on_cpu); + if (err < 0) + pr_warn("Watchdog could not be initialized"); + + return 0; +} +arch_initcall(powerpc_watchdog_init); + +static void handle_backtrace_ipi(struct pt_regs *regs) +{ + nmi_cpu_backtrace(regs); +} + +static void raise_backtrace_ipi(cpumask_t *mask) +{ + unsigned int cpu; + + for_each_cpu(cpu, mask) { + if (cpu == smp_processor_id()) + handle_backtrace_ipi(NULL); + else + smp_send_nmi_ipi(cpu, handle_backtrace_ipi, 1000000); + } +} + +void arch_trigger_cpumask_backtrace(const cpumask_t *mask, bool exclude_self) +{ + nmi_trigger_cpumask_backtrace(mask, exclude_self, raise_backtrace_ipi); +} _ -- To unsubscribe from this list: send the line "unsubscribe mm-commits" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
