>From 089dbf0216628ac6ae98742ab90725ca9c2bf201 Mon Sep 17 00:00:00 2001 From: <shikem...@huawei.com> Date: Tue, 10 Sep 2019 09:44:58 -0400 Subject: [PATCH] sched: fix migration to invalid cpu in __set_cpus_allowed_ptr
reason: migration to invalid cpu in __set_cpus_allowed_ptr archive path: patches/euleros/sched Oops occur when running qemu on arm64: Unable to handle kernel paging request at virtual address ffff000008effe40 Internal error: Oops: 96000007 [#1] SMP Process migration/0 (pid: 12, stack limit = 0x00000000084e3736) pstate: 20000085 (nzCv daIf -PAN -UAO) pc : __ll_sc___cmpxchg_case_acq_4+0x4/0x20 lr : move_queued_task.isra.21+0x124/0x298 ... Call trace: __ll_sc___cmpxchg_case_acq_4+0x4/0x20 __migrate_task+0xc8/0xe0 migration_cpu_stop+0x170/0x180 cpu_stopper_thread+0xec/0x178 smpboot_thread_fn+0x1ac/0x1e8 kthread+0x134/0x138 ret_from_fork+0x10/0x18 __set_cpus_allowed_ptr will choose an active dest_cpu in affinity mask to migrage the process if process is not currently running on any one of the CPUs specified in affinity mask.__set_cpus_allowed_ptr will choose an invalid dest_cpu(>= nr_cpu_ids, 1024 in my virtual machine) if CPUS in affinity mask are deactived by cpu_down after cpumask_intersects check.Cpumask_test_cpu of dest_cpu afterwards is overflow and may passes if corresponding bit is coincidentally set.As a consequence, kernel will access a invalid rq address associate with the invalid cpu in migration_cpu_stop->__migrate_task->move_queued_task and the Oops occurs. Process as follows may trigger the Oops: 1) A process repeatedly bind itself to cpu0 and cpu1 in turn by calling sched_setaffinity 2) A shell script repeatedly "echo 0 > /sys/devices/system/cpu/cpu1/online" and "echo 1 > /sys/devices/system/cpu/cpu1/online" in turn 3) Oops appears if the invalid cpu is set in memory after tested cpumask. Change-Id: I9c2f95aecd3da568991b7408397215f26c990e40 --- kernel/sched/core.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) diff --git a/kernel/sched/core.c b/kernel/sched/core.c index 4b63fef..5181ea9 100644 --- a/kernel/sched/core.c +++ b/kernel/sched/core.c @@ -1112,7 +1112,8 @@ static int __set_cpus_allowed_ptr(struct task_struct *p, if (cpumask_equal(&p->cpus_allowed, new_mask)) goto out; - if (!cpumask_intersects(new_mask, cpu_valid_mask)) { + dest_cpu = cpumask_any_and(cpu_valid_mask, new_mask); + if (dest_cpu >= nr_cpu_ids) { ret = -EINVAL; goto out; } @@ -1133,7 +1134,6 @@ static int __set_cpus_allowed_ptr(struct task_struct *p, if (cpumask_test_cpu(task_cpu(p), new_mask)) goto out; - dest_cpu = cpumask_any_and(cpu_valid_mask, new_mask); if (task_running(rq, p) || p->state == TASK_WAKING) { struct migration_arg arg = { p, dest_cpu }; /* Need help from migration thread: drop lock and wait. */ -- 1.8.5.6