Messages in this thread | | | Date | Mon, 4 Sep 2017 18:37:48 +0100 | From | Mark Rutland <> | Subject | Re: [PATCH 1/2] bus: arm-ccn: Fix use of smp_processor_id() in preemptible context |
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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.
Thanks, Mark.
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