On Mon, Sep 16, 2019 at 06:53:28AM +0000, KeMeng Shi wrote: > 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 (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 overflow 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. > > Process as follows may trigger the Oops: > 1) A process repeatedly binds 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. > > Signed-off-by: KeMeng Shi <[email protected]> > Reviewed-by: Valentin Schneider <[email protected]> > --- > Changes in v2: > -solve format problems in log > > 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 3c7b90bcbe4e..087f4ac30b60 100644 > --- a/kernel/sched/core.c > +++ b/kernel/sched/core.c > @@ -1656,7 +1656,8 @@ static int __set_cpus_allowed_ptr(struct task_struct *p, > if (cpumask_equal(p->cpus_ptr, 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; > } > @@ -1677,7 +1678,6 @@ 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. */ > -- > 2.19.1 > >
The cpu_active_mask might have changed in between. Your fix looks good to me. Thanks, Pavan -- Qualcomm India Private Limited, on behalf of Qualcomm Innovation Center, Inc. Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum, a Linux Foundation Collaborative Project.
