Rescuers are created when a workqueue with WQ_MEM_RECLAIM is allocated. It typically happens during the system boot. systemd switches the root filesystem from initrd to the booted system during boot. It kills processes that block the switch for too long. One of the process might be modprobe that tries to create a workqueue. These problems are hard to reproduce. Also alloc_workqueue() does not pass the error code. Make the debugging easier by printing an error, similar to create_worker().
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| @@ -4391,13 +4391,18 @@ static int init_rescuer(struct workqueue_struct *wq) · 4390 unmodified lines | ||
| 4391 | 4391 | return 0; |
| 4392 | 4392 | |
| 4393 | 4393 | rescuer = alloc_worker(NUMA_NO_NODE); |
| 4394 | − if (!rescuer) | |
| 4394 | + if (!rescuer) { | |
| 4395 | + pr_err("workqueue: Failed to allocate a rescuer for wq \"%s\"\n", | |
| 4396 | + wq->name); | |
| 4395 | 4397 | return -ENOMEM; |
| 4398 | + } | |
| 4396 | 4399 | |
| 4397 | 4400 | rescuer->rescue_wq = wq; |
| 4398 | 4401 | rescuer->task = kthread_create(rescuer_thread, rescuer, "%s", wq->name); |
| 4399 | 4402 | if (IS_ERR(rescuer->task)) { |
| 4400 | 4403 | ret = PTR_ERR(rescuer->task); |
| 4404 | + pr_err("workqueue: Failed to create a rescuer kthread for wq \"%s\": %pe", | |
| 4405 | + wq->name, ERR_PTR(ret)); | |
| 4401 | 4406 | kfree(rescuer); |
| 4402 | 4407 | return ret; |
| 4403 | 4408 | } |