On Mon, Feb 15, 2016 at 7:49 PM, Marc Zyngier <marc.zyngier@xxxxxxx> wrote: > On 15/02/16 18:41, Rafael J. Wysocki wrote: >> On Mon, Feb 15, 2016 at 6:05 PM, Guenter Roeck <linux@xxxxxxxxxxxx> wrote: >>> Rafael, >> >> Hi, >> >> Thanks for the report! >> >>> I see crashes in various arm qemu tests due to 'cpufreq: governor: Replace >>> timers with utilization update callbacks' with next-20160215. An example >>> crash log and bisect results are attached below. >>> >>> Please let me know if there is anything I can do to help tracking down >>> the problem. >> >> It looks like we've uncovered some nastiness in the arch ARM code (see below). >> >> [cut] >> >>> [ 1.340000] Unable to handle kernel NULL pointer dereference at virtual address 00000000 >>> [ 1.340000] pgd = c0204000 >>> [ 1.340000] [00000000] *pgd=00000000 >>> [ 1.340000] Internal error: Oops: 80000005 [#1] SMP ARM >>> [ 1.340000] Modules linked in: >>> [ 1.340000] CPU: 0 PID: 1 Comm: swapper/0 Not tainted 4.5.0-rc4-next-20160215 #1 >>> [ 1.340000] Hardware name: Generic OMAP3-GP (Flattened Device Tree) >>> [ 1.340000] task: cb060000 ti: cb05a000 task.ti: cb05a000 >>> [ 1.340000] PC is at 0x0 >>> [ 1.340000] LR is at arch_send_call_function_single_ipi+0x34/0x38 >> >> Since this is ARM, arch_send_call_function_single_ipi() looks like this: >> >> void arch_send_call_function_single_ipi(int cpu) >> { >> smp_cross_call(cpumask_of(cpu), IPI_CALL_FUNC_SINGLE); >> } >> >> so I'm not sure how the NULL pointer deref is possible even. >> >> The only thing coming to mind would be that cpumask_of(cpu) triggers >> this, but I'm not sure how exactly that can happen. >> >> I need help from somebody who knows how this low-level stuff works on ARM. > > Given that OMAP3 is a UP system, there is zero chance that it has > registered the magic hook that delivers IPIs (its interrupt controller > is not even capable of doing so). > > I don't really know the context, but IPIs on a UP system seem at best odd. That would explain it, thanks. So it looks like we should always use irq_work_queue() on UP even if CONFIG_SMP is set, shouldn't we? Thanks, Rafael -- To unsubscribe from this list: send the line "unsubscribe linux-next" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html