From: Joerg Roedel <[email protected]>
Currently the code to bring up secondary CPUs only checks
for cpu_online before it proceeds with launching the per-cpu
threads for the freshly booted remote CPU.
But the code to move these threads to the new CPU checks for
cpu_active to do so. If this check fails the threads end up
on the wrong CPU, causing warnings and bugs like:
WARNING: CPU: 0 PID: 1 at ../kernel/workqueue.c:4417
workqueue_cpu_up_callback
and/or:
kernel BUG at ../kernel/smpboot.c:135!
The reason is that the cpu_active bit for the new CPU
becomes visible significantly later than the cpu_online bit.
The reasons could be that the kernel runs in a KVM guest,
where the vCPU thread gets preempted when the cpu_online bit
is set, but with cpu_active still clear.
But this could also happen on bare-metal systems with lots
of CPUs. We have observed this issue on an 88 core x86
system on bare-metal.
To fix this issue, wait before the remote CPU is online
*and* active before launching the per-cpu threads.
Signed-off-by: Joerg Roedel <[email protected]>
---
arch/x86/kernel/smpboot.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/arch/x86/kernel/smpboot.c b/arch/x86/kernel/smpboot.c
index d3010aa..30b7b8b 100644
--- a/arch/x86/kernel/smpboot.c
+++ b/arch/x86/kernel/smpboot.c
@@ -1006,7 +1006,7 @@ 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 (!cpu_online(cpu) || !cpu_active(cpu)) {
cpu_relax();
touch_nmi_watchdog();
}
--
1.9.1
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