From mboxrd@z Thu Jan 1 00:00:00 1970 From: Vineet Gupta Subject: Re: Interesting csd deadlock on ARC Date: Tue, 23 Feb 2016 15:51:23 +0530 Message-ID: <56CC32A3.5020804@synopsys.com> References: <56C6BA82.1060909@synopsys.com> <56CBEC66.2030401@synopsys.com> <20160223095824.GH6356@twins.programming.kicks-ass.net> Mime-Version: 1.0 Content-Type: text/plain; charset="windows-1252" Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <20160223095824.GH6356@twins.programming.kicks-ass.net> Sender: linux-kernel-owner@vger.kernel.org To: Peter Zijlstra Cc: "linux-arch@vger.kernel.org" , Marc Zyngier , Frederic Weisbecker , lkml , Noam Camus , arcml List-Id: linux-arch.vger.kernel.org >> What I actually meant was is it OK for irq_work_queue_on() to be called locally >> (is this a sched bug/optimization(. Further if it is OK to be called, does it need >> to do behave more like irq_work_queue() i.e. call arch_irq_work_raise() or >> arch_send_call_function_single_ipi() is expected to handle sending IPI to self ! > > Right, so I'm not actually sure we started out with this requirement. > But you're not the first to run into this, see: > > lkml.kernel.org/r/CAJZ5v0gLankSuziQq25qTCyNqeOX43yD9jnJu_XXwbdyajfmKg@mail.gmail.com Thx for the link, very helpful. I've posted fix for ARC which uses software interrupt and is thus UP/SMP safe. > Initially I think irq_work_queue_on() was only used remotely, but I > think it makes sense to allow the current cpu, esp. since people seem to > be using it like that. > > Now the distinct difference between arch_irq_work_raise() and > arch_send_call_function_single_ipi() is that arch_irq_work_raise() > should be NMI-safe. Ok - so when I implement interrupt priorities (aka NMI for ARC), this needs to be highest. > > So on x86 it has to be extra careful about the lapic state, whereas the > regular IPI code doesn't. > > I seem to have forgotten the status of NMIs on ARC, but this is > something to make a note of. Not had a chance to go back to it since we last discussed. I've just been swamped with bug fixing like this one :-( Thx, -Vineet From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from us01smtprelay-2.synopsys.com ([198.182.60.111]:44752 "EHLO smtprelay.synopsys.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751198AbcBWKVm (ORCPT ); Tue, 23 Feb 2016 05:21:42 -0500 Subject: Re: Interesting csd deadlock on ARC References: <56C6BA82.1060909@synopsys.com> <56CBEC66.2030401@synopsys.com> <20160223095824.GH6356@twins.programming.kicks-ass.net> From: Vineet Gupta Message-ID: <56CC32A3.5020804@synopsys.com> Date: Tue, 23 Feb 2016 15:51:23 +0530 MIME-Version: 1.0 In-Reply-To: <20160223095824.GH6356@twins.programming.kicks-ass.net> Content-Type: text/plain; charset="windows-1252" Content-Transfer-Encoding: 7bit Sender: linux-arch-owner@vger.kernel.org List-ID: To: Peter Zijlstra Cc: "linux-arch@vger.kernel.org" , Marc Zyngier , Frederic Weisbecker , lkml , Noam Camus , arcml Message-ID: <20160223102123.5B8H4cq5AbCXX3nrNPZO5T0PGf6GTk-KiRE7N5F3TIk@z> >> What I actually meant was is it OK for irq_work_queue_on() to be called locally >> (is this a sched bug/optimization(. Further if it is OK to be called, does it need >> to do behave more like irq_work_queue() i.e. call arch_irq_work_raise() or >> arch_send_call_function_single_ipi() is expected to handle sending IPI to self ! > > Right, so I'm not actually sure we started out with this requirement. > But you're not the first to run into this, see: > > lkml.kernel.org/r/CAJZ5v0gLankSuziQq25qTCyNqeOX43yD9jnJu_XXwbdyajfmKg@mail.gmail.com Thx for the link, very helpful. I've posted fix for ARC which uses software interrupt and is thus UP/SMP safe. > Initially I think irq_work_queue_on() was only used remotely, but I > think it makes sense to allow the current cpu, esp. since people seem to > be using it like that. > > Now the distinct difference between arch_irq_work_raise() and > arch_send_call_function_single_ipi() is that arch_irq_work_raise() > should be NMI-safe. Ok - so when I implement interrupt priorities (aka NMI for ARC), this needs to be highest. > > So on x86 it has to be extra careful about the lapic state, whereas the > regular IPI code doesn't. > > I seem to have forgotten the status of NMIs on ARC, but this is > something to make a note of. Not had a chance to go back to it since we last discussed. I've just been swamped with bug fixing like this one :-( Thx, -Vineet