From 926963160ca4d6267957541a85591b7c426066d6 Mon Sep 17 00:00:00 2001 From: James Hogan Date: Wed, 13 Jul 2016 14:12:46 +0100 Subject: [PATCH] MIPS: SMP: Drop stop_this_cpu() cpu_foreign_map hack Commit cccf34e9411c ("MIPS: c-r4k: Fix cache flushing for MT cores") added the cpu_foreign_map cpumask containing a single VPE from each online core, and recalculated it when secondary CPUs are brought up. stop_this_cpu() was also updated to recalculate cpu_foreign_map, but with an additional hack before marking the CPU as offline to copy cpu_online_mask into cpu_foreign_map and perform an SMP memory barrier. This appears to have been intended to prevent cache management IPIs being missed when the VPE representing the core in cpu_foreign_map is taken offline while other VPEs remain online. Unfortunately there is nothing in this hack to prevent r4k_on_each_cpu() from reading the old cpu_foreign_map, and smp_call_function_many() from reading that new cpu_online_mask with the core's representative VPE marked offline. It then wouldn't send an IPI to any online VPEs of that core. stop_this_cpu() is only actually called in panic and system shutdown / halt / reboot situations, in which case all CPUs are going down and we don't really need to care about cache management, so drop this hack. Note that the __cpu_disable() case for CPU hotplug is handled in the previous commit, and no synchronisation is needed there due to the use of stop_machine() which prevents hotplug from taking place while any CPU has disabled preemption (as r4k_on_each_cpu() does). Signed-off-by: James Hogan Cc: Paul Burton Cc: Leonid Yegoshin Cc: linux-mips@linux-mips.org Patchwork: https://patchwork.linux-mips.org/patch/13796/ Signed-off-by: Ralf Baechle --- arch/mips/kernel/smp.c | 9 +-------- 1 file changed, 1 insertion(+), 8 deletions(-) diff --git a/arch/mips/kernel/smp.c b/arch/mips/kernel/smp.c index a4d4309ecff2..783d5f50ab9d 100644 --- a/arch/mips/kernel/smp.c +++ b/arch/mips/kernel/smp.c @@ -344,16 +344,9 @@ asmlinkage void start_secondary(void) static void stop_this_cpu(void *dummy) { /* - * Remove this CPU. Be a bit slow here and - * set the bits for every online CPU so we don't miss - * any IPI whilst taking this VPE down. + * Remove this CPU: */ - cpumask_copy(&cpu_foreign_map, cpu_online_mask); - - /* Make it visible to every other CPU */ - smp_mb(); - set_cpu_online(smp_processor_id(), false); calculate_cpu_foreign_map(); local_irq_disable(); -- 2.20.1