MIPS: Move idle task creation to work queue (6667deb6) · Commits · 戴 / test

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>

arch/mips/kernel/smp.c

+29 −2

Original line number	Diff line number	Diff line
		@@ -193,6 +193,22 @@ void __devinit smp_prepare_boot_cpu(void)
		*/
		static struct task_struct *cpu_idle_thread[NR_CPUS];

		struct create_idle {
		struct work_struct work;
		struct task_struct *idle;
		struct completion done;
		int cpu;
		};

		static void __cpuinit do_fork_idle(struct work_struct *work)
		{
		struct create_idle *c_idle =
		container_of(work, struct create_idle, work);

		c_idle->idle = fork_idle(c_idle->cpu);
		complete(&c_idle->done);
		}

		int __cpuinit __cpu_up(unsigned int cpu)
		{
		struct task_struct *idle;
		@@ -203,8 +219,19 @@ int __cpuinit __cpu_up(unsigned int cpu)
		* Linux can schedule processes on this slave.
		*/
		if (!cpu_idle_thread[cpu]) {
		idle = fork_idle(cpu);
		cpu_idle_thread[cpu] = idle;
		/*
		* Schedule work item to avoid forking user task
		* Ported from arch/x86/kernel/smpboot.c
		*/
		struct create_idle c_idle = {
		.cpu = cpu,
		.done = COMPLETION_INITIALIZER_ONSTACK(c_idle.done),
		};

		INIT_WORK_ONSTACK(&c_idle.work, do_fork_idle);
		schedule_work(&c_idle.work);
		wait_for_completion(&c_idle.done);
		idle = cpu_idle_thread[cpu] = c_idle.idle;

		if (IS_ERR(idle))
		panic(KERN_ERR "Fork failed for CPU %d", cpu);

Admin message