Messages in this thread Patch in this message | | | Date | Wed, 10 Dec 2014 15:08:57 +0100 (CET) | From | Thomas Gleixner <> | Subject | Re: [PATCH] powerpc: secondary CPUs signal to master before setting active and online (fixes kernel BUG at kernel/smpboot.c:134!) |
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On Tue, 9 Dec 2014, Linus Torvalds wrote: > On Mon, Dec 8, 2014 at 3:58 PM, Anton Blanchard <anton@samba.org> wrote: > > Hi Ingo, > > > >> At that point I thought the previous task_cpu() was somewhat ingrained > >> in the scheduler and came up with the patch. If not, we could go on a > >> hunt to see what else needs fixing. > > > > I had another look. The scheduled does indeed make assumptions about the > > previous task_cpu, but we have a hammer to fix it up called > > select_fallback_rq. > > > > I annotated select_fallback_rq, and did hit a case where the CPU was > > not active. ppc64 patch below. > > Anton, I'll assume I will get this through the usual powerpc pull requests? > > > I think x86 have a similar (although harder to hit) issue.
Indeed way harder to hit:
CPU 0 CPU 1
set_cpu_online(1, true) { while (!cpu_online(cpu1)) cpumask_set_cpu(1, to_cpumask(cpu_online_bits)); relax();
wakeup_thread_on_cpu1(); cpumask_set_cpu(1, to_cpumask(cpu_active_bits));
On bare metal probably impossible, but on virt it should be observable. Fix is simple.
Thanks,
tglx
diff --git a/arch/x86/kernel/smpboot.c b/arch/x86/kernel/smpboot.c index 668d8f2a8781..534f3384f03f 100644 --- a/arch/x86/kernel/smpboot.c +++ b/arch/x86/kernel/smpboot.c @@ -222,7 +222,6 @@ static void notrace start_secondary(void *unused) lock_vector_lock(); set_cpu_online(smp_processor_id(), true); unlock_vector_lock(); - per_cpu(cpu_state, smp_processor_id()) = CPU_ONLINE; x86_platform.nmi_init(); /* enable local interrupts */ @@ -234,6 +233,7 @@ static void notrace start_secondary(void *unused) x86_cpuinit.setup_percpu_clockev(); wmb(); + per_cpu(cpu_state, smp_processor_id()) = CPU_ONLINE; cpu_startup_entry(CPUHP_ONLINE); } @@ -932,7 +932,7 @@ int native_cpu_up(unsigned int cpu, struct task_struct *tidle) check_tsc_sync_source(cpu); local_irq_restore(flags); - while (!cpu_online(cpu)) { + while (per_cpu(cpu_state,cpu) != CPU_ONLINE) { cpu_relax(); touch_nmi_watchdog(); }
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