Re: [PATCH v3] workqueue: Fix WARN_ON_ONCE() triggers in worker_enter_idle()

[Naresh Kamboju]

+ Anders, LKFT

On Wed, 24 May 2023 at 09:23, Zqiang <qiang.zhang1211@xxxxxxxxx> wrote:
>
> Currently, the nr_running can be modified from timer tick, that means
> the timer tick can run in not-irq-protected critical section to modify
> nr_runnig, consider the following scenario:
>
> CPU0
> kworker/0:2 (events)
>    worker_clr_flags(worker, WORKER_PREP | WORKER_REBOUND);
>    ->pool->nr_running++;  (1)
>
>    process_one_work()
>    ->worker->current_func(work);
>      ->schedule()
>        ->wq_worker_sleeping()
>          ->worker->sleeping = 1;
>          ->pool->nr_running--;  (0)
>            ....
>        ->wq_worker_running()
>                ....
>                CPU0 by interrupt:
>                wq_worker_tick()
>                ->worker_set_flags(worker, WORKER_CPU_INTENSIVE);
>                  ->pool->nr_running--;  (-1)
>                  ->worker->flags |= WORKER_CPU_INTENSIVE;
>                ....
>          ->if (!(worker->flags & WORKER_NOT_RUNNING))
>            ->pool->nr_running++;    (will not execute)
>          ->worker->sleeping = 0;
>          ....
>     ->worker_clr_flags(worker, WORKER_CPU_INTENSIVE);
>       ->pool->nr_running++;  (0)
>     ....
>     worker_set_flags(worker, WORKER_PREP);
>     ->pool->nr_running--;   (-1)
>     ....
>     worker_enter_idle()
>     ->WARN_ON_ONCE(pool->nr_workers == pool->nr_idle && pool->nr_running);
>
> if the nr_workers is equal to nr_idle, due to the nr_running is not zero,
> will trigger WARN_ON_ONCE().
>
> [    2.460602] WARNING: CPU: 0 PID: 63 at kernel/workqueue.c:1999 worker_enter_idle+0xb2/0xc0
> [    2.462163] Modules linked in:
> [    2.463401] CPU: 0 PID: 63 Comm: kworker/0:2 Not tainted 6.4.0-rc2-next-20230519 #1
> [    2.463771] Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.14.0-2 04/01/2014
> [    2.465127] Workqueue:  0x0 (events)
> [    2.465678] RIP: 0010:worker_enter_idle+0xb2/0xc0
> ...
> [    2.472614] Call Trace:
> [    2.473152]  <TASK>
> [    2.474182]  worker_thread+0x71/0x430
> [    2.474992]  ? _raw_spin_unlock_irqrestore+0x28/0x50
> [    2.475263]  kthread+0x103/0x120
> [    2.475493]  ? __pfx_worker_thread+0x10/0x10
> [    2.476355]  ? __pfx_kthread+0x10/0x10
> [    2.476635]  ret_from_fork+0x2c/0x50
> [    2.477051]  </TASK>
>
> This commit therefore add the check of worker->sleeping in wq_worker_tick(),
> if the worker->sleeping is not zero, directly return.
>
> Reported-by: Naresh Kamboju <naresh.kamboju@xxxxxxxxxx>
> Closes: https://qa-reports.linaro.org/lkft/linux-next-master/build/next-20230519/testrun/17078554/suite/boot/test/clang-nightly-lkftconfig/log
> Signed-off-by: Zqiang <qiang.zhang1211@xxxxxxxxx>

Reported-by: Linux Kernel Functional Testing <lkft@xxxxxxxxxx>
Tested-by: Anders Roxell <anders.roxell@xxxxxxxxxx>

Since the probability of occurrence of this problem is only 3%,
Anders took this up and applied this on top of Linux next and
tested for 500 boot tests and all looked good.
Thanks, Anders.

- Naresh

> ---
>  kernel/workqueue.c | 15 ++++++++++-----
>  1 file changed, 10 insertions(+), 5 deletions(-)
>
> diff --git a/kernel/workqueue.c b/kernel/workqueue.c
> index 9c5c1cfa478f..a028b851333e 100644
> --- a/kernel/workqueue.c
> +++ b/kernel/workqueue.c
> @@ -1051,7 +1051,7 @@ void wq_worker_running(struct task_struct *task)
>  {
>         struct worker *worker = kthread_data(task);
>
> -       if (!worker->sleeping)
> +       if (!READ_ONCE(worker->sleeping))
>                 return;
>
>         /*
> @@ -1071,7 +1071,7 @@ void wq_worker_running(struct task_struct *task)
>          */
>         worker->current_at = worker->task->se.sum_exec_runtime;
>
> -       worker->sleeping = 0;
> +       WRITE_ONCE(worker->sleeping, 0);
>  }
>
>  /**
> @@ -1097,10 +1097,10 @@ void wq_worker_sleeping(struct task_struct *task)
>         pool = worker->pool;
>
>         /* Return if preempted before wq_worker_running() was reached */
> -       if (worker->sleeping)
> +       if (READ_ONCE(worker->sleeping))
>                 return;
>
> -       worker->sleeping = 1;
> +       WRITE_ONCE(worker->sleeping, 1);
>         raw_spin_lock_irq(&pool->lock);
>
>         /*
> @@ -1143,8 +1143,13 @@ void wq_worker_tick(struct task_struct *task)
>          * If the current worker is concurrency managed and hogged the CPU for
>          * longer than wq_cpu_intensive_thresh_us, it's automatically marked
>          * CPU_INTENSIVE to avoid stalling other concurrency-managed work items.
> +        *
> +        * The worker->sleeping is true means that the worker doing voluntary
> +        * switch and will not hogged the CPU, or the worker is running again
> +        * but the worker->sleeping has not been reset, in the process of executing
> +        * wq_worker_running().
>          */
> -       if ((worker->flags & WORKER_NOT_RUNNING) ||
> +       if ((worker->flags & WORKER_NOT_RUNNING) || READ_ONCE(worker->sleeping) ||
>             worker->task->se.sum_exec_runtime - worker->current_at <
>             wq_cpu_intensive_thresh_us * NSEC_PER_USEC)
>                 return;
> --
> 2.17.1
>