Messages in this thread Patch in this message | | | From | Valentin Schneider <> | Subject | Re: [PATCH] sched: fix migration to invalid cpu in __set_cpus_allowed_ptr | Date | Thu, 12 Sep 2019 23:09:20 +0100 |
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On 12/09/2019 02:55, shikemeng wrote: > From 089dbf0216628ac6ae98742ab90725ca9c2bf201 Mon Sep 17 00:00:00 2001 > From: <shikemeng@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 >
The above should probably be trimmed from the log.
> 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.
Right, cpumask_any_and() returns >= nr_cpu_ids when there isn't any valid CPU bit set.
> Cpumask_test_cpu of dest_cpu afterwards is overflow and may passes if corresponding bit > is coincidentally set.
Ouch. I was going to say the cpu_active_mask check from is_cpu_allowed() should've stopped the whole thing there, but AFAICT there's no safeguard against > nr_cpu_ids bit accesses. I see CONFIG_DEBUG_PER_CPU_MAPS should fire a warning for such accesses, but we don't enable it by default.
Would it make sense to do something like
return test_bit(...) && cpu < nr_cpu_ids;
for cpumask_test_cpu()? We still get the warn with the right config, but we prevent sneaky mistakes like this one. And it seems it's not the only one according to:
-- virtual patch virtual report
@nocheck@ expression E; identifier any_func =~ "^cpumask_any"; position pos; @@
E@pos = any_func(...); ... when != E >= nr_cpu_ids when != E < nr_cpu_ids
@script:python depends on nocheck && report@ p << nocheck.pos; @@ coccilib.report.print_report(p[0], "Missing cpumask_any_*() return value check!") ---
Some of those seem benign since they are on e.g. cpu_online_mask, some other are somewhat dubious (e.g. deadline.c::dl_task_can_attach()).
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
- This doesn't respect the 75 char per line limit - Change IDs don't belong here (we're not using Gerrit) - You're missing a Signed-off-by.
You'll find all the guidelines you need for formatting patches in Documentation/process/submitting-patches.rst.
> --- > 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 >
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