Commit 6667deb6 authored by Maksim Rayskiy's avatar Maksim Rayskiy Committed by Ralf Baechle
Browse files

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 <>

Signed-off-by: default avatarRalf Baechle <>
parent ba9786f3
......@@ -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);
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,
INIT_WORK_ONSTACK(&, do_fork_idle);
idle = cpu_idle_thread[cpu] = c_idle.idle;
if (IS_ERR(idle))
panic(KERN_ERR "Fork failed for CPU %d", cpu);
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