MIPS: Move idle task creation to work queue
To avoid forking usermode thread when creating an idle task, move fork_idle to a work queue. If kernel starts with maxcpus= option which does not bring all available cpus online at boot time, idle tasks for offline cpus are not created. If later offline cpus are hotplugged through sysfs, __cpu_up is called in the context of the user task, and fork_idle copies its non-zero mm pointer. This causes BUG() in per_cpu_trap_init. This also avoids issues with resource limits of the CPU writing to sysfs, containers, maybe others. Signed-off-by: Maksim Rayskiy <mrayskiy@broadcom.com> To: linux-mips@linux-mips.org Patchwork: https://patchwork.linux-mips.org/patch/2070/ Signed-off-by: Ralf Baechle <ralf@linux-mips.org>
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@ -193,6 +193,22 @@ void __devinit smp_prepare_boot_cpu(void)
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*/
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*/
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static struct task_struct *cpu_idle_thread[NR_CPUS];
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static struct task_struct *cpu_idle_thread[NR_CPUS];
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struct create_idle {
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struct work_struct work;
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struct task_struct *idle;
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struct completion done;
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int cpu;
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};
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static void __cpuinit do_fork_idle(struct work_struct *work)
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{
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struct create_idle *c_idle =
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container_of(work, struct create_idle, work);
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c_idle->idle = fork_idle(c_idle->cpu);
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complete(&c_idle->done);
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}
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int __cpuinit __cpu_up(unsigned int cpu)
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int __cpuinit __cpu_up(unsigned int cpu)
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{
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{
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struct task_struct *idle;
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struct task_struct *idle;
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@ -203,8 +219,19 @@ int __cpuinit __cpu_up(unsigned int cpu)
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* Linux can schedule processes on this slave.
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* Linux can schedule processes on this slave.
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*/
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*/
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if (!cpu_idle_thread[cpu]) {
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if (!cpu_idle_thread[cpu]) {
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idle = fork_idle(cpu);
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/*
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cpu_idle_thread[cpu] = idle;
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* Schedule work item to avoid forking user task
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* Ported from arch/x86/kernel/smpboot.c
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*/
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struct create_idle c_idle = {
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.cpu = cpu,
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.done = COMPLETION_INITIALIZER_ONSTACK(c_idle.done),
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};
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INIT_WORK_ONSTACK(&c_idle.work, do_fork_idle);
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schedule_work(&c_idle.work);
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wait_for_completion(&c_idle.done);
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idle = cpu_idle_thread[cpu] = c_idle.idle;
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if (IS_ERR(idle))
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if (IS_ERR(idle))
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panic(KERN_ERR "Fork failed for CPU %d", cpu);
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panic(KERN_ERR "Fork failed for CPU %d", cpu);
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