From: KeMeng Shi shikemeng@huawei.com
[ Upstream commit 714e501e16cd473538b609b3e351b2cc9f7f09ed ]
An oops can be triggered in the scheduler 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 (dest_cpu >= nr_cpu_ids, 1024 in my virtual machine) if CPUS in an affinity mask are deactived by cpu_down after cpumask_intersects check. cpumask_test_cpu() of dest_cpu afterwards is overflown and may pass if corresponding bit is coincidentally set. As a consequence, kernel will access an invalid rq address associate with the invalid CPU in migration_cpu_stop->__migrate_task->move_queued_task and the Oops occurs.
The reproduce the crash:
1) A process repeatedly binds itself to cpu0 and cpu1 in turn by calling sched_setaffinity.
2) A shell script repeatedly does "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.
Signed-off-by: KeMeng Shi shikemeng@huawei.com Signed-off-by: Peter Zijlstra (Intel) peterz@infradead.org Reviewed-by: Valentin Schneider valentin.schneider@arm.com Cc: Linus Torvalds torvalds@linux-foundation.org Cc: Peter Zijlstra peterz@infradead.org Cc: Thomas Gleixner tglx@linutronix.de Link: https://lkml.kernel.org/r/1568616808-16808-1-git-send-email-shikemeng@huawei... Signed-off-by: Ingo Molnar mingo@kernel.org Signed-off-by: Sasha Levin sashal@kernel.org --- 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 f4e050681ba1c..78ecdfae25b69 100644 --- a/kernel/sched/core.c +++ b/kernel/sched/core.c @@ -1077,7 +1077,8 @@ 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; } @@ -1098,7 +1099,6 @@ 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. */