Messages in this thread | | | Date | Thu, 10 May 2012 13:01:44 -0400 (EDT) | From | Igor Mammedov <> | Subject | Re: [PATCH] sched_groups are expected to be circular linked list, make it so right after allocation |
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----- Original Message ----- > From: "Peter Zijlstra" <peterz@infradead.org> > To: "Igor Mammedov" <imammedo@redhat.com> > Cc: "Jiang Liu" <liuj97@gmail.com>, linux-kernel@vger.kernel.org, mingo@kernel.org, pjt@google.com, > tglx@linutronix.de, "seto hidetoshi" <seto.hidetoshi@jp.fujitsu.com> > Sent: Thursday, May 10, 2012 3:45:44 PM > Subject: Re: [PATCH] sched_groups are expected to be circular linked list, make it so right after allocation > > On Thu, 2012-05-10 at 15:26 +0200, Igor Mammedov wrote: > > [ 141.699854] sched: Bonkers domain doesn't include its own cpu: 3 > > 0-1,3 > > [ 141.725038] sched: Bonkers domain doesn't include its own cpu: 3 > > 0-1 > > Whee!! so cpu_mask (active_mask) does include 3, but the tl->mask() > doesn't. > > > [ 141.775040] sched: Topology is hosed for CPU-3!! > > [ 141.775596] sched: domain: NODE 0-1 > > [ 141.776004] sched: group: 0-1 > > > This seems to suggest its the node topology being wrecked. > > which with your code-base would be > cpu_node_mask()->sched_domain_node_span().. > > Did you specify any node topology on the qemu command line? If not, > it > should all reduce to cpumask_of_node(0). > > identify_secondary_cpu()->identify_cpu()->numa_add_cpu() should set > that > bit. which is well before the CPU_ONLINE->cpuset_update_active_cpus() > sched domain rebuild. > > > Most puzzling. Can you dig a little deeper as to why these masks > might > be wrong? Also, can you reproduce on actual hardware? The reason I probably not
> never > use kvm or other virt for debugging is that I always end up spending > time chasing virt bugs, and I hate virt..
qemu started with -smp 4,sockets=4,cores=1,threads=1
I can answer it right away. It happens when one of cpus failed to come online on time and boot cpu decided to abandon attempt and exit do_boot_cpu with error. While exiting with error it clears some masks:
if (boot_error) { /* Try to put things back the way they were before ... */ numa_remove_cpu(cpu); /* was set by numa_add_cpu */
/* was set by do_boot_cpu() */ cpumask_clear_cpu(cpu, cpu_callout_mask);
/* was set by cpu_init() */ cpumask_clear_cpu(cpu, cpu_initialized_mask);
set_cpu_present(cpu, false); per_cpu(x86_cpu_to_apicid, cpu) = BAD_APICID; }
However cpu that has been blissfully forgotten, continues to boot and sets cpu_active_mask. So causing all sorts of havoc in places that use this mask. Then when next cpu is being onlined/offlined it eventually calls CPU_[ONLINE|DOWN]->cpuset_update_active_cpus() result is OOPS.
That is why I've posted https://lkml.org/lkml/2012/5/9/125 that prevent all of this from happening by 'gracefully' aborting boot process on failed cpu with necessary cleanup.
Checked Ingo's git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip.git:master races, that patches 1, 2, 4 are fixing, are still there. If it is preferable for this patches to go into -tip, then I'll rebase them on top of it and repost. ???
Please review them if you think it has a sense to fix races in mainline, before cpu-hotplug overhaul of this part is complete.
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