From: Maksim Rayskiy <mrayskiy@xxxxxxxxxxxx>
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.
To avoid this, release mm for idle task and reset the pointer after
fork_idle().
Signed-off-by: Maksim Rayskiy <mrayskiy@xxxxxxxxxxxx>
---
arch/mips/kernel/smp.c | 5 +++++
1 files changed, 5 insertions(+), 0 deletions(-)
diff --git a/arch/mips/kernel/smp.c b/arch/mips/kernel/smp.c
index 383aeb9..4593916 100644
--- a/arch/mips/kernel/smp.c
+++ b/arch/mips/kernel/smp.c
@@ -208,6 +208,11 @@ int __cpuinit __cpu_up(unsigned int cpu)
if (IS_ERR(idle))
panic(KERN_ERR "Fork failed for CPU %d", cpu);
+
+ if (idle->mm) {
+ mmput(idle->mm);
+ idle->mm = NULL;
+ }
} else {
idle = cpu_idle_thread[cpu];
init_idle(idle, cpu);
--
1.7.3.2
