> > 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 96f0e00378d4 ("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. Some small > changes to the generic code are required to support this. > > Signed-off-by: Daniel Thompson <daniel.thompson at linaro.org> > --- > arch/arm/kernel/smp.c | 7 +++++++ > lib/nmi_backtrace.c | 5 ++++- > 2 files changed, 11 insertions(+), 1 deletion(-) > > diff --git a/arch/arm/kernel/smp.c b/arch/arm/kernel/smp.c > index 48185a773852..4d8a80328c74 100644 > --- a/arch/arm/kernel/smp.c > +++ b/arch/arm/kernel/smp.c > @@ -748,6 +748,13 @@ 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. > + */ > + if (cpumask_test_cpu(smp_processor_id(), mask) && irqs_disabled()) > + nmi_cpu_backtrace(NULL); > + > smp_cross_call(mask, IPI_CPU_BACKTRACE); > } > > diff --git a/lib/nmi_backtrace.c b/lib/nmi_backtrace.c > index 88d3d32e5923..be0466a80d0b 100644 > --- a/lib/nmi_backtrace.c > +++ b/lib/nmi_backtrace.c > @@ -149,7 +149,10 @@ 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); > - show_regs(regs); > + if (regs) > + show_regs(regs); > + else > + dump_stack();
Better if dump_stack() is added in a separate patch, given that it is not mentioned in commit message. > this_cpu_write(printk_func, printk_func_save); > > cpumask_clear_cpu(cpu, to_cpumask(backtrace_mask)); > -- > 2.4.3 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/