From mboxrd@z Thu Jan 1 00:00:00 1970 Return-path: Message-ID: <51F2AC53.3070607@wwwdotorg.org> Date: Fri, 26 Jul 2013 11:05:23 -0600 From: Stephen Warren MIME-Version: 1.0 Subject: Re: [PATCH] ARM: kexec: offline non panic CPUs on Kdump panic References: <1374817287-27952-1-git-send-email-vijay.kilari@gmail.com> In-Reply-To: <1374817287-27952-1-git-send-email-vijay.kilari@gmail.com> List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "kexec" Errors-To: kexec-bounces+dwmw2=twosheds.infradead.org@lists.infradead.org To: vijay.kilari@gmail.com Cc: linux@arm.linux.org.uk, Prasun.Kapoor@caviumnetworks.com, will.deacon@arm.com, Vijaya Kumar K , kexec@lists.infradead.org, linux-arm-kernel@lists.infradead.org On 07/25/2013 11:41 PM, vijay.kilari@gmail.com wrote: > From: Vijaya Kumar K > > In case of normal kexec kernel load, all cpu's are offlined > before calling machine_kexec() under kernel_kexec() function. I'm not sure that's true, unless perhaps you have CONFIG_KEXEC_JUMP enabled? > But in case crash panic cpus are relaxed in > machine_crash_nonpanic_core() SMP function but not offlined. > > When crash kernel is loaded with kexec and on panic trigger > machine_kexec() checks for number of cpus online. > If more than one cpu is online machine_kexec() fails to load > with below error > > kexec: error: multiple CPUs still online > > In machine_crash_nonpanic_core() SMP function, offline CPU > before cpu_relax > diff --git a/arch/arm/kernel/machine_kexec.c b/arch/arm/kernel/machine_kexec.c > @@ -73,6 +73,7 @@ void machine_crash_nonpanic_core(void *unused) > crash_save_cpu(®s, smp_processor_id()); > flush_cache_all(); > > + set_cpu_online(smp_processor_id(), false); I'm not familiar with that API, but it looks like it's just setting the *current* CPU offline. That sounds problematic for two reasons: 1) Setting the current CPU offline sounds like a bad idea; after all, code is still running on it. Presumably you want to offline all other CPUs. 2) On a dual-CPU system, I guess this will leave a single CPU marked online, and hence satisfy the test in machine_kexec(). However, on a quad-core system, won't this just reduce the online CPU count from 4 to 3 and hence the test in machine_kexec() will still fail? Can't you call disable_nonboot_cpus() from machine_crash_nonpanic_core() just like machine_shutdown() does? _______________________________________________ kexec mailing list kexec@lists.infradead.org http://lists.infradead.org/mailman/listinfo/kexec