Messages in this thread | | | Subject | Re: [PATCH 1/2] bus: arm-ccn: Fix use of smp_processor_id() in preemptible context | From | Marc Zyngier <> | Date | Mon, 4 Sep 2017 18:59:40 +0100 |
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On 04/09/17 18:37, Mark Rutland wrote: > On Mon, Sep 04, 2017 at 06:30:40PM +0100, Marc Zyngier wrote: >> Booting a DEBUG_PREEMPT enabled kernel on a CCN-based system >> results in the following splat: >> >> [...] >> arm-ccn e8000000.ccn: No access to interrupts, using timer. >> BUG: using smp_processor_id() in preemptible [00000000] code: swapper/0/1 >> caller is debug_smp_processor_id+0x1c/0x28 >> CPU: 1 PID: 1 Comm: swapper/0 Not tainted 4.13.0 #6111 >> Hardware name: AMD Seattle/Seattle, BIOS 17:08:23 Jun 26 2017 >> Call trace: >> [<ffff000008089e78>] dump_backtrace+0x0/0x278 >> [<ffff00000808a22c>] show_stack+0x24/0x30 >> [<ffff000008bc3bc4>] dump_stack+0x8c/0xb0 >> [<ffff00000852b534>] check_preemption_disabled+0xfc/0x100 >> [<ffff00000852b554>] debug_smp_processor_id+0x1c/0x28 >> [<ffff000008551bd8>] arm_ccn_probe+0x358/0x4f0 >> [...] >> >> as we use smp_processor_id() in the wrong context. Turning this >> into a get_cpu()/put_cpu() does the trick. >> >> Signed-off-by: Marc Zyngier <marc.zyngier@arm.com> >> --- >> drivers/bus/arm-ccn.c | 3 ++- >> 1 file changed, 2 insertions(+), 1 deletion(-) >> >> diff --git a/drivers/bus/arm-ccn.c b/drivers/bus/arm-ccn.c >> index e8c6946fed9d..8502f1767024 100644 >> --- a/drivers/bus/arm-ccn.c >> +++ b/drivers/bus/arm-ccn.c >> @@ -1297,7 +1297,8 @@ static int arm_ccn_pmu_init(struct arm_ccn *ccn) >> } >> >> /* Pick one CPU which we will use to collect data from CCN... */ >> - cpumask_set_cpu(smp_processor_id(), &ccn->dt.cpu); >> + cpumask_set_cpu(get_cpu(), &ccn->dt.cpu); >> + put_cpu(); > > I think this isn't quite right, and we need to keep a CPU online until > we've registerd the hotplug callbacks. Otherwise, we could race with a > concurrent hotplug, and not migrate events appropriately. Right, I see. I'll respin that.
Thanks,
M. -- Jazz is not dead. It just smells funny...
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