Re: latest -git: WARNING: at arch/x86/kernel/ipi.c:123 send_IPI_mask_bitmask+0xc3/0xe0()

["H. Peter Anvin" <hpa@kernel.org>]

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Vegard Nossum wrote:
> 
> Hm.
> 
> Kernel fails to detect cpu1 at all.
> 
> I am currently unsure of whether it's your patch or not. But it's the
> same config that I've been booting for ages (and I copy it over for
> each new kernel version I check out).
> 
> Processor #0 (Bootup-CPU)
> I/O APIC #2 Version 32 at 0xFEC00000.
> Enabling APIC mode:  Flat.  Using 1 I/O APICs
> Processors: 1
> SMP: Allowing 1 CPUs, 0 hotplug CPUs
> mapped APIC to ffffb000 (fee00000)
> mapped IOAPIC to ffffa000 (fec00000)
> Allocating PCI resources starting at 50000000 (gap: 40000000:bee00000)
> PERCPU: Allocating 1221764 bytes of per cpu data
> NR_CPUS: 7, nr_cpu_ids: 1, nr_node_ids 1
> 
> I really don't get it. Is this something that can be caused by your
> patch _at all_ ?
> 

Could you try this patch?  It should (hopefully) tell us if there is any 
such invocations and what the call trace looks like.

	-hpa

[-- Attachment #2: smp-unplug-fault2.patch --]
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diff --git a/kernel/smp.c b/kernel/smp.c
index 782e2b9..95e1bad 100644
--- a/kernel/smp.c
+++ b/kernel/smp.c
@@ -210,8 +210,10 @@ int smp_call_function_single(int cpu, void (*func) (void *info), void *info,
 {
 	struct call_single_data d;
 	unsigned long flags;
-	/* prevent preemption and reschedule on another processor */
+	/* prevent preemption and reschedule on another processor,
+	   as well as CPU removal */
 	int me = get_cpu();
+	int err = 0;
 
 	/* Can deadlock when called with interrupts disabled */
 	WARN_ON(irqs_disabled());
@@ -220,7 +222,7 @@ int smp_call_function_single(int cpu, void (*func) (void *info), void *info,
 		local_irq_save(flags);
 		func(info);
 		local_irq_restore(flags);
-	} else {
+	} else if ((unsigned)cpu < NR_CPUS && cpu_online(cpu)) {
 		struct call_single_data *data = NULL;
 
 		if (!wait) {
@@ -236,10 +238,13 @@ int smp_call_function_single(int cpu, void (*func) (void *info), void *info,
 		data->func = func;
 		data->info = info;
 		generic_exec_single(cpu, data);
+	} else {
+		BUG();
+		err = -ENXIO;	/* CPU not online */
 	}
 
 	put_cpu();
-	return 0;
+	return err;
 }
 EXPORT_SYMBOL(smp_call_function_single);