+ Anders, LKFT

On Wed, 24 May 2023 at 09:23, Zqiang qiang.zhang1211@gmail.com 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@linaro.org Closes: https://qa-reports.linaro.org/lkft/linux-next-master/build/next-20230519/tes... Signed-off-by: Zqiang qiang.zhang1211@gmail.com

Reported-by: Linux Kernel Functional Testing lkft@linaro.org Tested-by: Anders Roxell anders.roxell@linaro.org

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