ARM: smp: Fix cpu_up() racing with sys_reboot.
Nothing stops a process from hotplugging in a CPU concurrently
with a sys_reboot() call. In such a situation we could have
ipi_cpu_stop() mark a cpu as 'offline' and _cpu_up() ignore the
fact that the CPU is not really offline and call the
CPU_UP_PREPARE notifier. When this happens stop_machine code will
complain that the cpu thread already exists and BUG_ON().
CPU0 CPU1
sys_reboot()
kernel_restart()
machine_restart()
machine_shutdown()
smp_send_stop()
... ipi_cpu_stop()
set_cpu_online(1, false)
local_irq_disable()
while(1)
<PREEMPT>
cpu_up()
_cpu_up()
if (!cpu_online(1))
__cpu_notify(CPU_UP_PREPARE...)
cpu_stop_cpu_callback()
BUG_ON(stopper->thread)
This is easily reproducible by hotplugging in and out in a tight
loop while also rebooting.
Since the CPU is not really offline and hasn't gone through the
proper steps to be marked as such, let's mark the CPU as inactive.
This is just as easily testable as online and avoids any possibility
of _cpu_up() trying to bring the CPU back online when it never was
offline to begin with.
Signed-off-by: Stephen Boyd <sboyd@codeaurora.org>
(cherry picked from commit 4a734179d918a4ee42c5fd6d54220eb6dd671ff0)
Change-Id: Id751200d45b58f12bf7d31ae5a7bc2ddd42ef92a
Signed-off-by: Sudhir Sharma <sudsha@codeaurora.org>
diff --git a/arch/arm/kernel/smp.c b/arch/arm/kernel/smp.c
index 7d26726..e46fd92 100644
--- a/arch/arm/kernel/smp.c
+++ b/arch/arm/kernel/smp.c
@@ -507,7 +507,7 @@
raw_spin_unlock(&stop_lock);
}
- set_cpu_online(cpu, false);
+ set_cpu_active(cpu, false);
local_fiq_disable();
local_irq_disable();
@@ -657,10 +657,10 @@
/* Wait up to one second for other CPUs to stop */
timeout = USEC_PER_SEC;
- while (num_online_cpus() > 1 && timeout--)
+ while (num_active_cpus() > 1 && timeout--)
udelay(1);
- if (num_online_cpus() > 1)
+ if (num_active_cpus() > 1)
pr_warning("SMP: failed to stop secondary CPUs\n");
smp_kill_cpus(&mask);