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Commit 6667deb6 authored by Maksim Rayskiy's avatar Maksim Rayskiy Committed by Ralf Baechle
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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: default avatarMaksim Rayskiy <mrayskiy@broadcom.com>
To: linux-mips@linux-mips.org
Patchwork: https://patchwork.linux-mips.org/patch/2070/


Signed-off-by: default avatarRalf Baechle <ralf@linux-mips.org>
parent ba9786f3

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);