From mboxrd@z Thu Jan 1 00:00:00 1970 From: tony@atomide.com (Tony Lindgren) Date: Mon, 15 Feb 2016 11:01:17 -0800 Subject: Crashes in arm qemu emulations due to 'cpufreq: governor: Replace timers with utilization ...' In-Reply-To: References: <20160215170527.GA24453@roeck-us.net> Message-ID: <20160215190116.GX19432@atomide.com> To: linux-arm-kernel@lists.infradead.org List-Id: linux-arm-kernel.lists.infradead.org * Rafael J. Wysocki [160215 10:44]: > On Mon, Feb 15, 2016 at 6:05 PM, Guenter Roeck 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. That's not even an SMP machine? I suspect a bunch of out of the 65 boot failures here are related to this: https://kernelci.org/boot/all/job/next/kernel/next-20160215/ The SMP ones seem to fail with some regulator issues? Regards, Tony