Re: [PATCH v2 3/3] kfence: test: try to avoid test_gfpzero trigger rcu_stall

[Marco Elver <elver@google.com>]

On Wed, 9 Mar 2022 at 09:19, 'Peng Liu' via kasan-dev
<kasan-dev@googlegroups.com> wrote:
>
> When CONFIG_KFENCE_NUM_OBJECTS is set to a big number, kfence
> kunit-test-case test_gfpzero will eat up nearly all the CPU's
> resources and rcu_stall is reported as the following log which
> is cut from a physical server.
>
>   rcu: INFO: rcu_sched self-detected stall on CPU
>   rcu:  68-....: (14422 ticks this GP) idle=6ce/1/0x4000000000000002
>   softirq=592/592 fqs=7500 (t=15004 jiffies g=10677 q=20019)
>   Task dump for CPU 68:
>   task:kunit_try_catch state:R  running task
>   stack:    0 pid: 9728 ppid:     2 flags:0x0000020a
>   Call trace:
>    dump_backtrace+0x0/0x1e4
>    show_stack+0x20/0x2c
>    sched_show_task+0x148/0x170
>    ...
>    rcu_sched_clock_irq+0x70/0x180
>    update_process_times+0x68/0xb0
>    tick_sched_handle+0x38/0x74
>    ...
>    gic_handle_irq+0x78/0x2c0
>    el1_irq+0xb8/0x140
>    kfree+0xd8/0x53c
>    test_alloc+0x264/0x310 [kfence_test]
>    test_gfpzero+0xf4/0x840 [kfence_test]
>    kunit_try_run_case+0x48/0x20c
>    kunit_generic_run_threadfn_adapter+0x28/0x34
>    kthread+0x108/0x13c
>    ret_from_fork+0x10/0x18
>
> To avoid rcu_stall and unacceptable latency, a schedule point is
> added to test_gfpzero.
>
> Signed-off-by: Peng Liu <liupeng256@huawei.com>

Reviewed-by: Marco Elver <elver@google.com>


> ---
>  mm/kfence/kfence_test.c | 1 +
>  1 file changed, 1 insertion(+)
>
> diff --git a/mm/kfence/kfence_test.c b/mm/kfence/kfence_test.c
> index caed6b4eba94..1b50f70a4c0f 100644
> --- a/mm/kfence/kfence_test.c
> +++ b/mm/kfence/kfence_test.c
> @@ -627,6 +627,7 @@ static void test_gfpzero(struct kunit *test)
>                         kunit_warn(test, "giving up ... cannot get same object back\n");
>                         return;
>                 }
> +               cond_resched();
>         }
>
>         for (i = 0; i < size; i++)
> --
> 2.18.0.huawei.25
>
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