From mboxrd@z Thu Jan 1 00:00:00 1970 From: Alexey Brodkin Subject: Re: Do we need to disable preemption in flush_tlb_range()? Date: Thu, 15 Mar 2018 09:39:31 +0000 Message-ID: <1521106770.11552.70.camel@synopsys.com> References: <1519917189.13866.6.camel@synopsys.com> <5a5c67c1-9f45-f908-2c8d-0914cd616a18@synopsys.com> <20180315082720.GT4064@hirez.programming.kicks-ass.net> Mime-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: base64 Return-path: In-Reply-To: <20180315082720.GT4064@hirez.programming.kicks-ass.net> Content-Language: en-US Content-ID: <4B6D4518BFFBD64793F3FEC19A670248@internal.synopsys.com> Sender: linux-kernel-owner@vger.kernel.org To: "peterz@infradead.org" Cc: "linux-arch@vger.kernel.org" , "linux-kernel@vger.kernel.org" , "Alexey.Brodkin@synopsys.com" , "Vineet.Gupta1@synopsys.com" , "linux-snps-arc@lists.infradead.org" List-Id: linux-arch.vger.kernel.org SGkgUGV0ZXIsDQoNCk9uIFRodSwgMjAxOC0wMy0xNSBhdCAwOToyNyArMDEwMCwgUGV0ZXIgWmlq bHN0cmEgd3JvdGU6DQo+IE9uIFdlZCwgTWFyIDE0LCAyMDE4IGF0IDAxOjE5OjAxUE0gLTA3MDAs IFZpbmVldCBHdXB0YSB3cm90ZToNCj4gPiArQ0MgUGV0ZXIgc2luY2Ugd2UgaGF2ZSBoaXMgYXR0 ZW50aW9uIDstKQ0KPiANCj4gWWVhaCwgdGltZXpvbmUgY29sbGlzaW9uIHRoZXJlLCBJIHR5cGlj YWxseSBzbGVlcCBhdCAxYW0gOy0pDQo+IA0KPiA+IE9uIDAzLzAxLzIwMTggMDc6MTMgQU0sIEFs ZXhleSBCcm9ka2luIHdyb3RlOg0KPiA+ID4gSGkgVmluZWV0LA0KPiA+ID4gDQo+ID4gPiBKdXN0 IG5vdGljZWQgdGhhdCBpbiBjb21tZW50cyBmb3Igc21wX2NhbGxfZnVuY3Rpb25fbWFueSgpIGl0 IGlzIHNhaWQgdGhhdA0KPiA+ID4gcHJlZW1wdGlvbiBtdXN0IGJlIGRpc2FibGVkIGR1cmluZyBp dHMgZXhlY3V0aW9uLiBBbmQgdGhhdCBmdW5jdGlvbiBnZXRzIGV4ZWN1dGVkDQo+ID4gPiBhbW9u ZyBvdGhlciB3YXlzIGxpa2UgdGhhdDoNCj4gPiA+IC0tLS0tLS0tLS0tLS0tLS0tLS0tLS0tLS0t PjgtLS0tLS0tLS0tLS0tLS0tLS0tLS0tLQ0KPiA+ID4gICAgZmx1c2hfdGxiX3JhbmdlKCkNCj4g PiA+ICAgICAgLT4gb25fZWFjaF9jcHVfbWFzaygpDQo+ID4gPiAgICAgICAgICAgLT4gc21wX2Nh bGxfZnVuY3Rpb25fbWFueSgpDQo+ID4gPiAtLS0tLS0tLS0tLS0tLS0tLS0tLS0tLS0tLT44LS0t LS0tLS0tLS0tLS0tLS0tLS0tLS0NCj4gPiANCj4gPiBJbiBnZW5lcmFsIEkgcHJlZmVyIG5vdCB0 byAtIFBldGVyIHdoYXQgc2F5IHlvdSA/DQo+IA0KPiBUaGUgY29tbWVudCB3aXRoIHNtcF9jYWxs X2Z1bmN0aW9uX21hbnkoKSBpcyBjb3JyZWN0LCBpdCByZWxpZXMgb24NCj4gcHJlZW1wdGlvbiBi ZWluZyBkaXNhYmxlZCBpbiBhIG51bWJlciBvZiB3YXlzLiBJIHdvdWxkIGV4cGVjdA0KPiB0aGlz X2NwdV9wdHIoKSBmb3IgZXhhbXBsZSB0byBjb21wbGFpbiB3aGVuIHVzZWQgd2l0aCBwcmVlbXB0 aW9uDQo+IGVuYWJsZWQgKENPTkZJR19ERUJVR19QUkVFTVBUKS4NCg0KSSBqdXN0IHRyaWVkIENP TkZJR19ERUJVR19QUkVFTVBUIGFuZCB0aGUgb25seSB0aGluZyBJIGdvdCB3YXMgdGhhdDoNCi0t LS0tLS0tLS0tLS0tLS0tLS0tLS0tLS0tPjgtLS0tLS0tLS0tLS0tLS0tLS0tLS0tLQ0KQVJDIHBl cmYgICAgICAgIDogOCBjb3VudGVycyAoMzIgYml0cyksIDMyIGNvbmRpdGlvbnMsIFtvdmVyZmxv dyBJUlEgc3VwcG9ydF0NCkJVRzogdXNpbmcgc21wX3Byb2Nlc3Nvcl9pZCgpIGluIHByZWVtcHRp YmxlIFswMDAwMDAwMF0gY29kZTogc3dhcHBlci8wLzENCmNhbGxlciBpcyBhcmNfcG11X2Rldmlj ZV9wcm9iZSsweDI0ZS8weDI5Yw0KQ1BVOiAwIFBJRDogMSBDb21tOiBzd2FwcGVyLzAgTm90IHRh aW50ZWQgNC4xNC4xNCsgIzY3DQoNClN0YWNrIFRyYWNlOg0KICBhcmNfdW53aW5kX2NvcmUuY29u c3Rwcm9wLjErMHhkMC8weGY0DQogIGR1bXBfc3RhY2srMHg2NC8weDdjDQogIGRlYnVnX3NtcF9w cm9jZXNzb3JfaWQrMHhiOC8weGJjDQogIGFyY19wbXVfZGV2aWNlX3Byb2JlKzB4MjRlLzB4Mjlj DQogIHBsYXRmb3JtX2Rydl9wcm9iZSsweDI2LzB4NWMNCiAgcmVhbGx5X3Byb2JlKzB4Mjg4LzB4 MzM4DQogIF9fZHJpdmVyX2F0dGFjaCsweGM0LzB4YzgNCiAgYnVzX2Zvcl9lYWNoX2RldisweDM4 LzB4NzANCiAgYnVzX2FkZF9kcml2ZXIrMHgxMmEvMHgxOGMNCiAgZHJpdmVyX3JlZ2lzdGVyKzB4 NTAvMHhlYw0KICBkb19vbmVfaW5pdGNhbGwrMHgzMi8weDEwOA0KICBrZXJuZWxfaW5pdF9mcmVl YWJsZSsweGZlLzB4MTg4DQotLS0tLS0tLS0tLS0tLS0tLS0tLS0tLS0tLT44LS0tLS0tLS0tLS0t LS0tLS0tLS0tLS0NCg0KVGhhdCBoYXBwZW5zIGJlY2F1c2UgaW4gUE1VIHByb2JlIHJvdXRpbmUg d2Ugd2FudCB0bw0KY29uZmlndXJlIElSUSBoYW5kbGVycyBvbiBhbGwgb3RoZXIgY29yZXM6DQot LS0tLS0tLS0tLS0tLS0tLS0tLS0tLS0tLT44LS0tLS0tLS0tLS0tLS0tLS0tLS0tLS0NCiAgYXJj X3BtdV9kZXZpY2VfcHJvYmUoKSAtPg0KICAgIG9uX2VhY2hfY3B1KGFyY19jcHVfcG11X2lycV9p bml0LCAmaXJxLCAxKTogcHJlZW1wdF9kaXNhYmxlKCkgLT4NCiAgICAgIGVuYWJsZV9wZXJjcHVf aXJxKGlycSwgSVJRX1RZUEVfTk9ORSkgLT4NCiAgICAgICAgc21wX3Byb2Nlc3Nvcl9pZCgpIHdp dGggZGlzYWJsZWQgcHJlZW1wdGlvbi4NCi0tLS0tLS0tLS0tLS0tLS0tLS0tLS0tLS0tPjgtLS0t LS0tLS0tLS0tLS0tLS0tLS0tLQ0KDQpXaGljaCBwb3NlcyBhbm90aGVyIHByZWVtcHRpb24gcmVs YXRlZCBxdWVzdGlvbiAtIGhvdyBkbyBJUlEgc2V0dXAgb24NCmFsbCBjb3JlcyBwcm9wZXJseT8g OikNCg0KLUFsZXhleQ== From mboxrd@z Thu Jan 1 00:00:00 1970 From: Alexey.Brodkin@synopsys.com (Alexey Brodkin) Date: Thu, 15 Mar 2018 09:39:31 +0000 Subject: Do we need to disable preemption in flush_tlb_range()? In-Reply-To: <20180315082720.GT4064@hirez.programming.kicks-ass.net> References: <1519917189.13866.6.camel@synopsys.com> <5a5c67c1-9f45-f908-2c8d-0914cd616a18@synopsys.com> <20180315082720.GT4064@hirez.programming.kicks-ass.net> List-ID: Message-ID: <1521106770.11552.70.camel@synopsys.com> To: linux-snps-arc@lists.infradead.org Hi Peter, On Thu, 2018-03-15@09:27 +0100, Peter Zijlstra wrote: > On Wed, Mar 14, 2018@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