+CC some more folks for intc/irq insights - please see question at the bottom ! On 03/15/2018 02:39 AM, Alexey Brodkin wrote: > Hi Peter, > > On Thu, 2018-03-15 at 09:27 +0100, Peter Zijlstra wrote: >> On Wed, Mar 14, 2018 at 01:19:01PM -0700, Vineet Gupta wrote: >>> +CC Peter since we have his attention ;-) >> >> Yeah, timezone collision there, I typically sleep at 1am ;-) >> >>> On 03/01/2018 07:13 AM, Alexey Brodkin wrote: >>>> Hi Vineet, >>>> >>>> Just noticed that in comments for smp_call_function_many() it is said that >>>> preemption must be disabled during its execution. And that function gets executed >>>> among other ways like that: >>>> -------------------------->8----------------------- >>>> flush_tlb_range() >>>> -> on_each_cpu_mask() >>>> -> smp_call_function_many() >>>> -------------------------->8----------------------- >>> >>> In general I prefer not to - Peter what say you ? >> >> The comment with smp_call_function_many() is correct, it relies on >> preemption being disabled in a number of ways. I would expect >> this_cpu_ptr() for example to complain when used with preemption >> enabled (CONFIG_DEBUG_PREEMPT). > > I just tried CONFIG_DEBUG_PREEMPT and the only thing I got was that: > -------------------------->8----------------------- > ARC perf : 8 counters (32 bits), 32 conditions, [overflow IRQ support] > BUG: using smp_processor_id() in preemptible [00000000] code: swapper/0/1 > caller is arc_pmu_device_probe+0x24e/0x29c > CPU: 0 PID: 1 Comm: swapper/0 Not tainted 4.14.14+ #67 > > Stack Trace: > arc_unwind_core.constprop.1+0xd0/0xf4 > dump_stack+0x64/0x7c > debug_smp_processor_id+0xb8/0xbc > arc_pmu_device_probe+0x24e/0x29c > platform_drv_probe+0x26/0x5c > really_probe+0x288/0x338 > __driver_attach+0xc4/0xc8 > bus_for_each_dev+0x38/0x70 > bus_add_driver+0x12a/0x18c > driver_register+0x50/0xec > do_one_initcall+0x32/0x108 > kernel_init_freeable+0xfe/0x188 > -------------------------->8----------------------- > > That happens because in PMU probe routine we want to > configure IRQ handlers on all other cores: > -------------------------->8----------------------- > arc_pmu_device_probe() -> > on_each_cpu(arc_cpu_pmu_irq_init, &irq, 1): preempt_disable() -> > enable_percpu_irq(irq, IRQ_TYPE_NONE) -> > smp_processor_id() with disabled preemption. > -------------------------->8----------------------- > > Which poses another preemption related question - how do IRQ setup on > all cores properly? :) > > -Alexey >
