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From:   Zqiang <qiang.zhang1211@gmail.com>
To:     tj@kernel.org, jiangshanlai@gmail.com, naresh.kamboju@linaro.org,
        qiang.zhang1211@gmail.com
Cc:     linux-kernel@vger.kernel.org
Subject: [PATCH] workqueue: Fix warning triggered when nr_running is checked in worker_enter_idle()
Date:   Tue, 23 May 2023 11:19:33 +0800
Message-Id: <20230523031933.13421-1-qiang.zhang1211@gmail.com>
Precedence: bulk

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()
         ->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_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 irq protection in wq_worker_running() to
block timer tick modify nr_running.

Reported-by: Naresh Kamboju <naresh.kamboju@linaro.org>
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@gmail.com>
---
 kernel/workqueue.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/kernel/workqueue.c b/kernel/workqueue.c
index 9c5c1cfa478f..f8d739fef311 100644
--- a/kernel/workqueue.c
+++ b/kernel/workqueue.c
@@ -1060,10 +1060,9 @@ void wq_worker_running(struct task_struct *task)
 	 * and leave with an unexpected pool->nr_running == 1 on the newly unbound
 	 * pool. Protect against such race.
 	 */
-	preempt_disable();
+	local_irq_disable();
 	if (!(worker->flags & WORKER_NOT_RUNNING))
 		worker->pool->nr_running++;
-	preempt_enable();
 
 	/*
 	 * CPU intensive auto-detection cares about how long a work item hogged
@@ -1072,6 +1071,7 @@ void wq_worker_running(struct task_struct *task)
 	worker->current_at = worker->task->se.sum_exec_runtime;
 
 	worker->sleeping = 0;
+	local_irq_enable();
 }
 
 /**
-- 
2.17.1