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Currently, the nmi_cpu_backtrace() declines to produce backtraces for idle CPUs. This is a good choice in the common case in which problems are caused only by non-idle CPUs. However, there are occasionally situations in which idle CPUs are helping to cause problems. This commit therefore adds an nmi_backtrace.backtrace_idle kernel boot parameter that causes nmi_cpu_backtrace() to dump stacks even of idle CPUs. Signed-off-by: Paul E. McKenney <paulmck@kernel.org> Cc: Jonathan Corbet <corbet@lwn.net> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: Andrew Morton <akpm@linux-foundation.org> Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org> Cc: <linux-doc@vger.kernel.org>
114 lines
3.1 KiB
C
114 lines
3.1 KiB
C
// SPDX-License-Identifier: GPL-2.0
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/*
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* NMI backtrace support
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*
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* Gratuitously copied from arch/x86/kernel/apic/hw_nmi.c by Russell King,
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* with the following header:
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*
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* HW NMI watchdog support
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*
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* started by Don Zickus, Copyright (C) 2010 Red Hat, Inc.
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*
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* Arch specific calls to support NMI watchdog
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*
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* Bits copied from original nmi.c file
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*/
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#include <linux/cpumask.h>
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#include <linux/delay.h>
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#include <linux/kprobes.h>
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#include <linux/nmi.h>
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#include <linux/cpu.h>
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#include <linux/sched/debug.h>
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#ifdef arch_trigger_cpumask_backtrace
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/* For reliability, we're prepared to waste bits here. */
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static DECLARE_BITMAP(backtrace_mask, NR_CPUS) __read_mostly;
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/* "in progress" flag of arch_trigger_cpumask_backtrace */
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static unsigned long backtrace_flag;
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/*
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* When raise() is called it will be passed a pointer to the
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* backtrace_mask. Architectures that call nmi_cpu_backtrace()
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* directly from their raise() functions may rely on the mask
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* they are passed being updated as a side effect of this call.
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*/
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void nmi_trigger_cpumask_backtrace(const cpumask_t *mask,
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bool exclude_self,
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void (*raise)(cpumask_t *mask))
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{
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int i, this_cpu = get_cpu();
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if (test_and_set_bit(0, &backtrace_flag)) {
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/*
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* If there is already a trigger_all_cpu_backtrace() in progress
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* (backtrace_flag == 1), don't output double cpu dump infos.
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*/
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put_cpu();
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return;
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}
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cpumask_copy(to_cpumask(backtrace_mask), mask);
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if (exclude_self)
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cpumask_clear_cpu(this_cpu, to_cpumask(backtrace_mask));
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/*
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* Don't try to send an NMI to this cpu; it may work on some
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* architectures, but on others it may not, and we'll get
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* information at least as useful just by doing a dump_stack() here.
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* Note that nmi_cpu_backtrace(NULL) will clear the cpu bit.
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*/
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if (cpumask_test_cpu(this_cpu, to_cpumask(backtrace_mask)))
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nmi_cpu_backtrace(NULL);
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if (!cpumask_empty(to_cpumask(backtrace_mask))) {
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pr_info("Sending NMI from CPU %d to CPUs %*pbl:\n",
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this_cpu, nr_cpumask_bits, to_cpumask(backtrace_mask));
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raise(to_cpumask(backtrace_mask));
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}
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/* Wait for up to 10 seconds for all CPUs to do the backtrace */
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for (i = 0; i < 10 * 1000; i++) {
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if (cpumask_empty(to_cpumask(backtrace_mask)))
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break;
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mdelay(1);
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touch_softlockup_watchdog();
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}
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/*
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* Force flush any remote buffers that might be stuck in IRQ context
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* and therefore could not run their irq_work.
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*/
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printk_safe_flush();
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clear_bit_unlock(0, &backtrace_flag);
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put_cpu();
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}
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// Dump stacks even for idle CPUs.
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static bool backtrace_idle;
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module_param(backtrace_idle, bool, 0644);
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bool nmi_cpu_backtrace(struct pt_regs *regs)
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{
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int cpu = smp_processor_id();
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if (cpumask_test_cpu(cpu, to_cpumask(backtrace_mask))) {
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if (!READ_ONCE(backtrace_idle) && regs && cpu_in_idle(instruction_pointer(regs))) {
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pr_warn("NMI backtrace for cpu %d skipped: idling at %pS\n",
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cpu, (void *)instruction_pointer(regs));
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} else {
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pr_warn("NMI backtrace for cpu %d\n", cpu);
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if (regs)
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show_regs(regs);
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else
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dump_stack();
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}
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cpumask_clear_cpu(cpu, to_cpumask(backtrace_mask));
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return true;
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}
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return false;
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}
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NOKPROBE_SYMBOL(nmi_cpu_backtrace);
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#endif
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