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Currently the nmi_backtrace is serialized against other CPUs because the messages are sent to the NMI buffers. Once these buffers are removed, only the dumped stack will be serialized against other CPUs (via the printk_cpu_lock). Also serialize the nmi_backtrace banner and regs using the printk_cpu_lock so that per-CPU serialization will be preserved even after the NMI buffers are removed. Signed-off-by: John Ogness <john.ogness@linutronix.de> Reviewed-by: Petr Mladek <pmladek@suse.com> Signed-off-by: Petr Mladek <pmladek@suse.com> Link: https://lore.kernel.org/r/20210715193359.25946-2-john.ogness@linutronix.de
122 lines
3.3 KiB
C
122 lines
3.3 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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unsigned long flags;
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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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/*
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* Allow nested NMI backtraces while serializing
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* against other CPUs.
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*/
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printk_cpu_lock_irqsave(flags);
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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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printk_cpu_unlock_irqrestore(flags);
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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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