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. Turn this into a get_cpu()/put_cpu() that extends over the CPU hotplug registration, making sure that we don't race against a CPU down operation. Signed-off-by: Marc Zyngier <[email protected]> --- drivers/bus/arm-ccn.c | 4 +++- 1 file changed, 3 insertions(+), 1 deletion(-) diff --git a/drivers/bus/arm-ccn.c b/drivers/bus/arm-ccn.c index e8c6946fed9d..8614d7fa457e 100644 --- a/drivers/bus/arm-ccn.c +++ b/drivers/bus/arm-ccn.c @@ -1297,7 +1297,7 @@ 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); /* Also make sure that the overflow interrupt is handled by this CPU */ if (ccn->irq) { @@ -1314,10 +1314,12 @@ static int arm_ccn_pmu_init(struct arm_ccn *ccn) cpuhp_state_add_instance_nocalls(CPUHP_AP_PERF_ARM_CCN_ONLINE, &ccn->dt.node); + put_cpu(); return 0; error_pmu_register: error_set_affinity: + put_cpu(); ida_simple_remove(&arm_ccn_pmu_ida, ccn->dt.id); for (i = 0; i < ccn->num_xps; i++) writel(0, ccn->xp[i].base + CCN_XP_DT_CONTROL); -- 2.11.0
