Re: [RFC PATCH] workqueue: Fix rescuer task's name truncated

[Wenchao Hao <haowenchao2@huawei.com>]

On 2024/4/24 2:21, Wenchao Hao wrote:
> Task comm of task is limitted to 16, prefix "kworker/R-" is added for
> rescuer worker's task, which cause most task name is truncated as
> following:
> 
> root   81  0.0  0.0  0  0 ?   I<   11:18   0:00 [kworker/R-xprti]
> root   82  0.0  0.0  0  0 ?   I<   11:18   0:00 [kworker/R-cfg80]
> root   85  0.0  0.0  0  0 ?   I<   11:18   0:00 [kworker/R-nfsio]
> root   86  0.0  0.0  0  0 ?   I<   11:18   0:00 [kworker/R-xfsal]
> root   87  0.0  0.0  0  0 ?   I<   11:18   0:00 [kworker/R-xfs_m]
> root   88  0.0  0.0  0  0 ?   I<   11:18   0:00 [kworker/R-acpi_]
> root   93  0.0  0.0  0  0 ?   I<   11:18   0:00 [kworker/R-iscsi]
> root   95  0.0  0.0  0  0 ?   I<   11:18   0:00 [kworker/R-scsi_]
> root   97  0.0  0.0  0  0 ?   I<   11:18   0:00 [kworker/R-scsi_]
> root   99  0.0  0.0  0  0 ?   I<   11:18   0:00 [kworker/R-scsi_]
> 
> I want to fix this issue by split rescuer name to 2 part like other
> kworker, the normal part is "kworker/R" which is set to task_struct's comm,
> another part is wq->name which is added to kworker's desc. These 2 parts
> would be merged in wq_worker_comm().
> 
> Fixes: b6a46f7263bd ("workqueue: Rename rescuer kworker")
> 
> Signed-off-by: Wenchao Hao <haowenchao2@huawei.com>
> ---
>   kernel/workqueue.c | 6 +++++-
>   1 file changed, 5 insertions(+), 1 deletion(-)
> 
> diff --git a/kernel/workqueue.c b/kernel/workqueue.c
> index 0066c8f6c154..0ce9e8597a4d 100644
> --- a/kernel/workqueue.c
> +++ b/kernel/workqueue.c
> @@ -5430,7 +5430,7 @@ static int init_rescuer(struct workqueue_struct *wq)
>   	}
>   
>   	rescuer->rescue_wq = wq;
> -	rescuer->task = kthread_create(rescuer_thread, rescuer, "kworker/R-%s", wq->name);
> +	rescuer->task = kthread_create(rescuer_thread, rescuer, "kworker/R");
>   	if (IS_ERR(rescuer->task)) {
>   		ret = PTR_ERR(rescuer->task);
>   		pr_err("workqueue: Failed to create a rescuer kthread for wq \"%s\": %pe",
> @@ -5439,6 +5439,8 @@ static int init_rescuer(struct workqueue_struct *wq)
>   		return ret;
>   	}
>   
> +	snprintf(rescuer->desc, sizeof(rescuer->desc), "%s", wq->name);
> +
>   	wq->rescuer = rescuer;
>   	if (wq->flags & WQ_UNBOUND)
>   		kthread_bind_mask(rescuer->task, wq_unbound_cpumask);
> @@ -6289,6 +6291,8 @@ void wq_worker_comm(char *buf, size_t size, struct task_struct *task)
>   						  worker->desc);
>   			}
>   			raw_spin_unlock_irq(&pool->lock);
> +		} else if (worker->desc[0] != '\0') {
> +			scnprintf(buf + off, size - off, "-%s", worker->desc);
>   		}


Hi Tejun and all:

I added another logic in wq_worker_comm() to append worker's desc when
worker is not attached to a work pool. I don't know why the origin
logic only append worker's desc when worker is attached to a work pool,
so I am not sure if it's safe to using worker here directly.

>   	}
>