From cc53d4d32e68f15530abbc42e27ed724db07358d Mon Sep 17 00:00:00 2001 From: Stephen Boyd Date: Tue, 21 Aug 2012 20:19:10 -0700 Subject: [PATCH] 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) 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 (cherry picked from commit 4a734179d918a4ee42c5fd6d54220eb6dd671ff0) Change-Id: Id751200d45b58f12bf7d31ae5a7bc2ddd42ef92a Signed-off-by: Sudhir Sharma --- arch/arm/kernel/smp.c | 6 +++--- 1 file changed, 3 insertions(+), 3 deletions(-) diff --git a/arch/arm/kernel/smp.c b/arch/arm/kernel/smp.c index 7d26726a9f8..e46fd92b451 100644 --- a/arch/arm/kernel/smp.c +++ b/arch/arm/kernel/smp.c @@ -507,7 +507,7 @@ static void ipi_cpu_stop(unsigned int cpu) 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 @@ void smp_send_stop(void) /* 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);