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Date: Mon, 20 May 2024 12:30:18 -1000
From: Tejun Heo <tj@...nel.org>
To: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: Jan Engelhardt <jengelh@...i.de>, Craig Small <csmall@....com.au>,
Yafang Shao <laoar.shao@...il.com>, linux-kernel@...r.kernel.org,
Lai Jiangshan <jiangshanlai@...il.com>
Subject: [PATCH workqueue/for-6.10-fixes] workqueue: Refactor worker ID
formatting and make wq_worker_comm() use full ID string
Currently, worker ID formatting is open coded in create_worker(),
init_rescuer() and worker_thread() (for %WORKER_DIE case). The formatted ID
is saved into task->comm and wq_worker_comm() uses it as the base name to
append extra information to when generating the name to be shown as.
However, TASK_COMM_LEN is only 16 leading to badly truncated names for
rescuers. For example, the rescuer for the inet_frag_wq workqueue becomes:
$ ps -ef | grep '[k]worker/R-inet'
root 483 2 0 Apr26 ? 00:00:00 [kworker/R-inet_]
Even for non-rescue workers, it's easy to run over 15 characters on
moderately large machines.
Fit it by consolidating worker ID formatting into a new helper
format_worker_id() and calling it from wq_worker_comm() to obtain the
untruncated worker ID.
$ ps -ef | grep '[k]worker/R-inet'
root 60 2 0 12:10 ? 00:00:00 [kworker/R-inet_frag_wq]
Signed-off-by: Tejun Heo <tj@...nel.org>
Reported-by: Jan Engelhardt <jengelh@...i.de>
Suggested-by: Linus Torvalds <torvalds@...ux-foundation.org>
---
(cc'ing LKML and Lai)
On Mon, May 20, 2024 at 10:17:00AM -0700, Linus Torvalds wrote:
> Oh well. I suspect this would be trivial to fix. I think the
> get_kthread_comm() should use the full name, and only *then* attach
> the extra worker pool information if it exists..
>
> Tejun?
Yeah, looks like even the unbound worker IDs are getting truncated on larger
machines. This patch should fix it. I'll apply it to wq/for-6.10-fixes soon.
> Also, independently of the WQ worker issue, I do think we could
> possibly expand TASK_COMM_LEN a bit more. 16 bytes is too short for
> user-level names too, and while it's seldom used for 'ps', it's
> visible in things like oops messages etc where it gets truncated.
That'd be great. ISTR this being discussed a while ago. Am I imagining that
we were going to raise this to 32?
Thanks.
kernel/workqueue.c | 51 ++++++++++++++++++++++++++++++++++-----------------
1 file changed, 34 insertions(+), 17 deletions(-)
--- a/kernel/workqueue.c
+++ b/kernel/workqueue.c
@@ -125,6 +125,7 @@ enum wq_internal_consts {
HIGHPRI_NICE_LEVEL = MIN_NICE,
WQ_NAME_LEN = 32,
+ WORKER_ID_LEN = 10 + WQ_NAME_LEN, /* "kworker/R-" + WQ_NAME_LEN */
};
/*
@@ -2742,6 +2743,26 @@ static void worker_detach_from_pool(stru
complete(detach_completion);
}
+static int format_worker_id(char *buf, size_t size, struct worker *worker,
+ struct worker_pool *pool)
+{
+ if (worker->rescue_wq)
+ return scnprintf(buf, size, "kworker/R-%s",
+ worker->rescue_wq->name);
+
+ if (pool) {
+ if (pool->cpu >= 0)
+ return scnprintf(buf, size, "kworker/%d:%d%s",
+ pool->cpu, worker->id,
+ pool->attrs->nice < 0 ? "H" : "");
+ else
+ return scnprintf(buf, size, "kworker/u%d:%d",
+ pool->id, worker->id);
+ } else {
+ return scnprintf(buf, size, "kworker/dying");
+ }
+}
+
/**
* create_worker - create a new workqueue worker
* @pool: pool the new worker will belong to
@@ -2758,7 +2779,6 @@ static struct worker *create_worker(stru
{
struct worker *worker;
int id;
- char id_buf[23];
/* ID is needed to determine kthread name */
id = ida_alloc(&pool->worker_ida, GFP_KERNEL);
@@ -2777,17 +2797,14 @@ static struct worker *create_worker(stru
worker->id = id;
if (!(pool->flags & POOL_BH)) {
- if (pool->cpu >= 0)
- snprintf(id_buf, sizeof(id_buf), "%d:%d%s", pool->cpu, id,
- pool->attrs->nice < 0 ? "H" : "");
- else
- snprintf(id_buf, sizeof(id_buf), "u%d:%d", pool->id, id);
+ char id_buf[WORKER_ID_LEN];
+ format_worker_id(id_buf, sizeof(id_buf), worker, pool);
worker->task = kthread_create_on_node(worker_thread, worker,
- pool->node, "kworker/%s", id_buf);
+ pool->node, "%s", id_buf);
if (IS_ERR(worker->task)) {
if (PTR_ERR(worker->task) == -EINTR) {
- pr_err("workqueue: Interrupted when creating a worker thread \"kworker/%s\"\n",
+ pr_err("workqueue: Interrupted when creating a worker thread \"%s\"\n",
id_buf);
} else {
pr_err_once("workqueue: Failed to create a worker thread: %pe",
@@ -3350,7 +3367,6 @@ woke_up:
raw_spin_unlock_irq(&pool->lock);
set_pf_worker(false);
- set_task_comm(worker->task, "kworker/dying");
ida_free(&pool->worker_ida, worker->id);
worker_detach_from_pool(worker);
WARN_ON_ONCE(!list_empty(&worker->entry));
@@ -5542,6 +5558,7 @@ static int wq_clamp_max_active(int max_a
static int init_rescuer(struct workqueue_struct *wq)
{
struct worker *rescuer;
+ char id_buf[WORKER_ID_LEN];
int ret;
if (!(wq->flags & WQ_MEM_RECLAIM))
@@ -5555,7 +5572,9 @@ static int init_rescuer(struct workqueue
}
rescuer->rescue_wq = wq;
- rescuer->task = kthread_create(rescuer_thread, rescuer, "kworker/R-%s", wq->name);
+ format_worker_id(id_buf, sizeof(id_buf), rescuer, NULL);
+
+ rescuer->task = kthread_create(rescuer_thread, rescuer, "%s", id_buf);
if (IS_ERR(rescuer->task)) {
ret = PTR_ERR(rescuer->task);
pr_err("workqueue: Failed to create a rescuer kthread for wq \"%s\": %pe",
@@ -6384,19 +6403,15 @@ void show_freezable_workqueues(void)
/* used to show worker information through /proc/PID/{comm,stat,status} */
void wq_worker_comm(char *buf, size_t size, struct task_struct *task)
{
- int off;
-
- /* always show the actual comm */
- off = strscpy(buf, task->comm, size);
- if (off < 0)
- return;
-
/* stabilize PF_WQ_WORKER and worker pool association */
mutex_lock(&wq_pool_attach_mutex);
if (task->flags & PF_WQ_WORKER) {
struct worker *worker = kthread_data(task);
struct worker_pool *pool = worker->pool;
+ int off;
+
+ off = format_worker_id(buf, size, worker, pool);
if (pool) {
raw_spin_lock_irq(&pool->lock);
@@ -6415,6 +6430,8 @@ void wq_worker_comm(char *buf, size_t si
}
raw_spin_unlock_irq(&pool->lock);
}
+ } else {
+ strscpy(buf, task->comm, size);
}
mutex_unlock(&wq_pool_attach_mutex);
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