This flag simplifies debugging of NO_HZ_FULL kernels when processes are running in PR_CPU_ISOLATED_ENABLE mode. Such processes should get no interrupts from the kernel, and if they do, when this boot flag is specified a kernel stack dump on the console is generated.
It's possible to use ftrace to simply detect whether a cpu_isolated core has unexpectedly entered the kernel. But what this boot flag does is allow the kernel to provide better diagnostics, e.g. by reporting in the IPI-generating code what remote core and context is preparing to deliver an interrupt to a cpu_isolated core. It may be worth considering other ways to generate useful debugging output rather than console spew, but for now that is simple and direct. Signed-off-by: Chris Metcalf <[email protected]> --- Documentation/kernel-parameters.txt | 6 ++++++ arch/tile/mm/homecache.c | 5 ++++- include/linux/tick.h | 2 ++ kernel/irq_work.c | 4 +++- kernel/sched/core.c | 18 ++++++++++++++++++ kernel/signal.c | 5 +++++ kernel/smp.c | 4 ++++ kernel/softirq.c | 6 ++++++ 8 files changed, 48 insertions(+), 2 deletions(-) diff --git a/Documentation/kernel-parameters.txt b/Documentation/kernel-parameters.txt index 1d6f0459cd7b..76e8e2ff4a0a 100644 --- a/Documentation/kernel-parameters.txt +++ b/Documentation/kernel-parameters.txt @@ -749,6 +749,12 @@ bytes respectively. Such letter suffixes can also be entirely omitted. /proc/<pid>/coredump_filter. See also Documentation/filesystems/proc.txt. + cpu_isolated_debug [KNL] + In kernels built with CONFIG_NO_HZ_FULL and booted + in nohz_full= mode, this setting will generate console + backtraces when the kernel is about to interrupt a + task that has requested PR_CPU_ISOLATED_ENABLE. + cpuidle.off=1 [CPU_IDLE] disable the cpuidle sub-system diff --git a/arch/tile/mm/homecache.c b/arch/tile/mm/homecache.c index 40ca30a9fee3..f336880e1b01 100644 --- a/arch/tile/mm/homecache.c +++ b/arch/tile/mm/homecache.c @@ -31,6 +31,7 @@ #include <linux/smp.h> #include <linux/module.h> #include <linux/hugetlb.h> +#include <linux/tick.h> #include <asm/page.h> #include <asm/sections.h> @@ -83,8 +84,10 @@ static void hv_flush_update(const struct cpumask *cache_cpumask, * Don't bother to update atomically; losing a count * here is not that critical. */ - for_each_cpu(cpu, &mask) + for_each_cpu(cpu, &mask) { ++per_cpu(irq_stat, cpu).irq_hv_flush_count; + tick_nohz_cpu_isolated_debug(cpu); + } } /* diff --git a/include/linux/tick.h b/include/linux/tick.h index f79f6945f762..ed65551e2315 100644 --- a/include/linux/tick.h +++ b/include/linux/tick.h @@ -159,6 +159,7 @@ extern void __tick_nohz_task_switch(struct task_struct *tsk); extern void tick_nohz_cpu_isolated_enter(void); extern void tick_nohz_cpu_isolated_syscall(int nr); extern void tick_nohz_cpu_isolated_exception(void); +extern void tick_nohz_cpu_isolated_debug(int cpu); #else static inline bool tick_nohz_full_enabled(void) { return false; } static inline bool tick_nohz_full_cpu(int cpu) { return false; } @@ -172,6 +173,7 @@ static inline bool tick_nohz_is_cpu_isolated(void) { return false; } static inline void tick_nohz_cpu_isolated_enter(void) { } static inline void tick_nohz_cpu_isolated_syscall(int nr) { } static inline void tick_nohz_cpu_isolated_exception(void) { } +static inline void tick_nohz_cpu_isolated_debug(int cpu) { } #endif static inline bool is_housekeeping_cpu(int cpu) diff --git a/kernel/irq_work.c b/kernel/irq_work.c index cbf9fb899d92..7f35c90346de 100644 --- a/kernel/irq_work.c +++ b/kernel/irq_work.c @@ -75,8 +75,10 @@ bool irq_work_queue_on(struct irq_work *work, int cpu) if (!irq_work_claim(work)) return false; - if (llist_add(&work->llnode, &per_cpu(raised_list, cpu))) + if (llist_add(&work->llnode, &per_cpu(raised_list, cpu))) { + tick_nohz_cpu_isolated_debug(cpu); arch_send_call_function_single_ipi(cpu); + } return true; } diff --git a/kernel/sched/core.c b/kernel/sched/core.c index 78b4bad10081..c8388f9206b2 100644 --- a/kernel/sched/core.c +++ b/kernel/sched/core.c @@ -743,6 +743,24 @@ bool sched_can_stop_tick(void) return true; } + +/* Enable debugging of any interrupts of cpu_isolated cores. */ +static int cpu_isolated_debug; +static int __init cpu_isolated_debug_func(char *str) +{ + cpu_isolated_debug = true; + return 1; +} +__setup("cpu_isolated_debug", cpu_isolated_debug_func); + +void tick_nohz_cpu_isolated_debug(int cpu) +{ + if (cpu_isolated_debug && tick_nohz_full_cpu(cpu) && + (cpu_curr(cpu)->cpu_isolated_flags & PR_CPU_ISOLATED_ENABLE)) { + pr_err("Interrupt detected for cpu_isolated cpu %d\n", cpu); + dump_stack(); + } +} #endif /* CONFIG_NO_HZ_FULL */ void sched_avg_update(struct rq *rq) diff --git a/kernel/signal.c b/kernel/signal.c index 836df8dac6cc..90ee460c2586 100644 --- a/kernel/signal.c +++ b/kernel/signal.c @@ -684,6 +684,11 @@ int dequeue_signal(struct task_struct *tsk, sigset_t *mask, siginfo_t *info) */ void signal_wake_up_state(struct task_struct *t, unsigned int state) { +#ifdef CONFIG_NO_HZ_FULL + /* If the task is being killed, don't complain about cpu_isolated. */ + if (state & TASK_WAKEKILL) + t->cpu_isolated_flags = 0; +#endif set_tsk_thread_flag(t, TIF_SIGPENDING); /* * TASK_WAKEKILL also means wake it up in the stopped/traced/killable diff --git a/kernel/smp.c b/kernel/smp.c index 07854477c164..6b7d8e2c8af4 100644 --- a/kernel/smp.c +++ b/kernel/smp.c @@ -14,6 +14,7 @@ #include <linux/smp.h> #include <linux/cpu.h> #include <linux/sched.h> +#include <linux/tick.h> #include "smpboot.h" @@ -178,6 +179,7 @@ static int generic_exec_single(int cpu, struct call_single_data *csd, * locking and barrier primitives. Generic code isn't really * equipped to do the right thing... */ + tick_nohz_cpu_isolated_debug(cpu); if (llist_add(&csd->llist, &per_cpu(call_single_queue, cpu))) arch_send_call_function_single_ipi(cpu); @@ -457,6 +459,8 @@ void smp_call_function_many(const struct cpumask *mask, } /* Send a message to all CPUs in the map */ + for_each_cpu(cpu, cfd->cpumask) + tick_nohz_cpu_isolated_debug(cpu); arch_send_call_function_ipi_mask(cfd->cpumask); if (wait) { diff --git a/kernel/softirq.c b/kernel/softirq.c index 479e4436f787..333872925ff6 100644 --- a/kernel/softirq.c +++ b/kernel/softirq.c @@ -24,6 +24,7 @@ #include <linux/ftrace.h> #include <linux/smp.h> #include <linux/smpboot.h> +#include <linux/context_tracking.h> #include <linux/tick.h> #include <linux/irq.h> @@ -335,6 +336,11 @@ void irq_enter(void) _local_bh_enable(); } + if (context_tracking_cpu_is_enabled() && + context_tracking_in_user() && + !in_interrupt()) + tick_nohz_cpu_isolated_debug(smp_processor_id()); + __irq_enter(); } -- 2.1.2 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
