This is a note to let you know that I've just added the patch titled
powerpc: Secondary CPUs must set cpu_callin_map after setting active and online
to the 3.18-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
powerpc-secondary-cpus-must-set-cpu_callin_map-after-setting-active-and-online.patch
and it can be found in the queue-3.18 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
>From 7c5c92ed56d932b2c19c3f8aea86369509407d33 Mon Sep 17 00:00:00 2001
From: Anton Blanchard <anton@xxxxxxxxx>
Date: Tue, 9 Dec 2014 10:58:19 +1100
Subject: powerpc: Secondary CPUs must set cpu_callin_map after setting active and online
From: Anton Blanchard <anton@xxxxxxxxx>
commit 7c5c92ed56d932b2c19c3f8aea86369509407d33 upstream.
I have a busy ppc64le KVM box where guests sometimes hit the infamous
"kernel BUG at kernel/smpboot.c:134!" issue during boot:
BUG_ON(td->cpu != smp_processor_id());
Basically a per CPU hotplug thread scheduled on the wrong CPU. The oops
output confirms it:
CPU: 0
Comm: watchdog/130
The problem is that we aren't ensuring the CPU active and online bits are set
before allowing the master to continue on. The master unparks the secondary
CPUs kthreads and the scheduler looks for a CPU to run on. It calls
select_task_rq and realises the suggested CPU is not in the cpus_allowed
mask. It then ends up in select_fallback_rq, and since the active and
online bits aren't set we choose some other CPU to run on.
Signed-off-by: Anton Blanchard <anton@xxxxxxxxx>
Signed-off-by: Michael Ellerman <mpe@xxxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
arch/powerpc/kernel/smp.c | 9 ++++++++-
1 file changed, 8 insertions(+), 1 deletion(-)
--- a/arch/powerpc/kernel/smp.c
+++ b/arch/powerpc/kernel/smp.c
@@ -700,7 +700,6 @@ void start_secondary(void *unused)
smp_store_cpu_info(cpu);
set_dec(tb_ticks_per_jiffy);
preempt_disable();
- cpu_callin_map[cpu] = 1;
if (smp_ops->setup_cpu)
smp_ops->setup_cpu(cpu);
@@ -739,6 +738,14 @@ void start_secondary(void *unused)
notify_cpu_starting(cpu);
set_cpu_online(cpu, true);
+ /*
+ * CPU must be marked active and online before we signal back to the
+ * master, because the scheduler needs to see the cpu_online and
+ * cpu_active bits set.
+ */
+ smp_wmb();
+ cpu_callin_map[cpu] = 1;
+
local_irq_enable();
cpu_startup_entry(CPUHP_ONLINE);
Patches currently in stable-queue which might be from anton@xxxxxxxxx are
queue-3.18/powerpc-secondary-cpus-must-set-cpu_callin_map-after-setting-active-and-online.patch
queue-3.18/powerpc-fix-bad-null-pointer-check-in-udbg_uart_getc_poll.patch
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