From: Tiejun Chen Subject: cpu_down: move migrate_enable() back Date: Thu, 7 Nov 2013 10:06:07 +0800 Origin: https://www.kernel.org/pub/linux/kernel/projects/rt/4.4/patches-4.4.1-rt6.tar.xz Commit 08c1ab68, "hotplug-use-migrate-disable.patch", intends to use migrate_enable()/migrate_disable() to replace that combination of preempt_enable() and preempt_disable(), but actually in !CONFIG_PREEMPT_RT_FULL case, migrate_enable()/migrate_disable() are still equal to preempt_enable()/preempt_disable(). So that followed cpu_hotplug_begin()/cpu_unplug_begin(cpu) would go schedule() to trigger schedule_debug() like this: _cpu_down() | + migrate_disable() = preempt_disable() | + cpu_hotplug_begin() or cpu_unplug_begin() | + schedule() | + __schedule() | + preempt_disable(); | + __schedule_bug() is true! So we should move migrate_enable() as the original scheme. Signed-off-by: Tiejun Chen --- kernel/cpu.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) --- a/kernel/cpu.c +++ b/kernel/cpu.c @@ -657,6 +657,7 @@ static int _cpu_down(unsigned int cpu, i err = -EBUSY; goto restore_cpus; } + migrate_enable(); cpu_hotplug_begin(); err = cpu_unplug_begin(cpu); @@ -741,7 +742,6 @@ static int _cpu_down(unsigned int cpu, i out_release: cpu_unplug_done(cpu); out_cancel: - migrate_enable(); cpu_hotplug_done(); if (!err) cpu_notify_nofail(CPU_POST_DEAD | mod, hcpu);