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Mon, 03 Aug 2020 01:16:27 -0700 (PDT) Date: Mon, 3 Aug 2020 11:16:25 +0300 From: Vladimir Oltean To: Kurt Kanzenbach Cc: Alison Wang , catalin.marinas@arm.com, will@kernel.org, paulmck@kernel.org, mw@semihalf.com, leoyang.li@nxp.com, vladimir.oltean@nxp.com, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, Anna-Maria Gleixner , Thomas Gleixner Subject: Re: [RFC PATCH] arm64: defconfig: Disable fine-grained task level IRQ time accounting Message-ID: <20200803081625.czdfwcpw5emcd4ls@skbuf> References: <20200729033934.22349-1-alison.wang@nxp.com> <877dumbtoi.fsf@kurt> <20200729094943.lsmhsqlnl7rlnl6f@skbuf> <87mu3ho48v.fsf@kurt> <20200730082228.r24zgdeiofvwxijm@skbuf> <873654m9zi.fsf@kurt> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <873654m9zi.fsf@kurt> Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Aug 03, 2020 at 10:04:01AM +0200, Kurt Kanzenbach wrote: > On Thu Jul 30 2020, Vladimir Oltean wrote: > > On Thu, Jul 30, 2020 at 09:23:44AM +0200, Kurt Kanzenbach wrote: > >> On Wed Jul 29 2020, Vladimir Oltean wrote: > >> > For more context, here is my original report of the issue: > >> > https://lkml.org/lkml/2020/6/4/1062 > >> > > >> > Just like you, I could not reproduce the RCU stalls and system hang on a > >> > 5.6-rt kernel, just on mainline and derivatives, using the plain > >> > defconfig. > >> > > >> > The issue is not specific to Layerscape or i.MX8, but rather I was able > >> > to see the same behavior on Marvell Armada 37xx as well as Qualcomm > >> > MSM8976. > >> > > >> > So, while of course I agree that disabling IRQ time accounting for arm64 > >> > isn't a real solution, it isn't by far an exaggerated proposal either. > >> > Nonetheless, the patch is just a RFC and should be treated as such. We > >> > are at a loss when it comes to debugging this any further and we would > >> > appreciate some pointers. > >> > >> Yeah, sure. I'll try to reproduce this issue first. So it triggers with: > >> > >> * arm64 > >> * mainline, not -rt kernel > >> * opened serial console > >> * irq accounting enabled > >> > >> Anything else? > >> > >> Thanks, > >> Kurt > > > > Thanks for giving a helping hand, Kurt. The defconfig should be enough. > > In the interest of full disclosure, the only arm64 device on which we > > didn't reproduce this was the 16-core LX2160A. But we did reproduce on > > that with maxcpus=1 though. And also on msm8976 with all 8 cores booted. > > Just mentioning this in case you're testing on a 16-core system, you > > might want to reduce the number a bit. > > OK. I've reproduced it on a Marvell Armada SoC with v5.6 mainline. See > splats below. Running with irq time accounting enabled, kills the > machine immediately. However, I'm not getting the possible deadlock > warnings in 8250 as you did. So that might be unrelated. > Yes, the console lockdep warnings are unrelated. They are discussed here: https://lore.kernel.org/lkml/CAHQZ30BnfX+gxjPm1DUd5psOTqbyDh4EJE=2=VAMW_VDafctkA@mail.gmail.com/ > Unfortunately I have no idea what to debug here. > > Thanks, > Kurt So, this means we could submit a formal version of this patch? :) Thanks, -Vladimir