ARM: 8439/1: Fix backtrace generation when IPI is masked (0768330d) · Commits · 戴 / test

Currently on ARM when <SysRq-L> is triggered from an interrupt handler (e.g. a SysRq issued using UART or kbd) the main CPU will wedge for ten seconds with interrupts masked before issuing a backtrace for every CPU except itself. The new backtrace code introduced by commit ("ARM: add basic support for on-demand backtrace of other CPUs") does not work correctly when run from an interrupt handler because IPI_CPU_BACKTRACE is used to generate the backtrace on all CPUs but cannot preempt the current calling context. This can be fixed by detecting that the calling context cannot be preempted and issuing the backtrace directly in this case. Issuing directly leaves us without any pt_regs to pass to nmi_cpu_backtrace() so we also modify the generic code to call dump_stack() when its argument is NULL. Acked-by:

Hillf Danton <hillf.zj@alibaba-inc.com> Acked-by:

Thomas Gleixner <tglx@linutronix.de> Signed-off-by:

Daniel Thompson <daniel.thompson@linaro.org> Signed-off-by:

Russell King <rmk+kernel@arm.linux.org.uk>

arch/arm/kernel/smp.c

+9 −0

Original line number	Diff line number	Diff line
		@@ -749,6 +749,15 @@ core_initcall(register_cpufreq_notifier);

		static void raise_nmi(cpumask_t *mask)
		{
		/*
		* Generate the backtrace directly if we are running in a calling
		* context that is not preemptible by the backtrace IPI. Note
		* that nmi_cpu_backtrace() automatically removes the current cpu
		* from mask.
		*/
		if (cpumask_test_cpu(smp_processor_id(), mask) && irqs_disabled())
		nmi_cpu_backtrace(NULL);

		smp_cross_call(mask, IPI_CPU_BACKTRACE);
		}

lib/nmi_backtrace.c

+10 −1

Original line number	Diff line number	Diff line
		@@ -43,6 +43,12 @@ static void print_seq_line(struct nmi_seq_buf *s, int start, int end)
		printk("%.*s", (end - start) + 1, buf);
		}

		/*
		* When raise() is called it will be is passed a pointer to the
		* backtrace_mask. Architectures that call nmi_cpu_backtrace()
		* directly from their raise() functions may rely on the mask
		* they are passed being updated as a side effect of this call.
		*/
		void nmi_trigger_all_cpu_backtrace(bool include_self,
		void (raise)(cpumask_t mask))
		{
		@@ -149,7 +155,10 @@ bool nmi_cpu_backtrace(struct pt_regs *regs)
		/* Replace printk to write into the NMI seq */
		this_cpu_write(printk_func, nmi_vprintk);
		pr_warn("NMI backtrace for cpu %d\n", cpu);
		if (regs)
		show_regs(regs);
		else
		dump_stack();
		this_cpu_write(printk_func, printk_func_save);

		cpumask_clear_cpu(cpu, to_cpumask(backtrace_mask));

Admin message