kernel/workqueue.c | 6 +++++- 1 file changed, 5 insertions(+), 1 deletion(-)
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);
}
}
--
2.32.0On 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.
> }
>
On Tue, Apr 23, 2024 at 12:55:22PM +0800, Wenchao Hao wrote: > 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. Hi Wenchao, A worker description is always updated under the per-pool workqueue lock. You can indeed use the rescuer's own description to store its associated workqueue name - good idea. We know the caller of set_worker_desc() will never touch a rescuer. For this unique rescuer case, if I understand correctly, you can read a rescuer's description outside the per-pool workqueue lock; albeit, you need to prevent a race with destroy_workqueue() to avoid a use-after-free. Kind regards, -- Aaron Tomlin
On 4/24/24 3:12 PM, Aaron Tomlin wrote:
> On Tue, Apr 23, 2024 at 12:55:22PM +0800, Wenchao Hao wrote:
>> 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.
>
> Hi Wenchao,
>
> A worker description is always updated under the per-pool workqueue lock.
> You can indeed use the rescuer's own description to store its associated
> workqueue name - good idea. We know the caller of set_worker_desc() will
> never touch a rescuer. For this unique rescuer case, if I understand
> correctly, you can read a rescuer's description outside the per-pool
> workqueue lock; albeit, you need to prevent a race with destroy_workqueue()
> to avoid a use-after-free.
>
Hi Aaron, thanks a lot for your reply.
I think destroy_workqueue() may not race with wq_worker_comm(),
wq_pool_attach_mutex is used to avoid race, below is my analysis.
(Welcome to point out if my understand is incorrect)
t1 which call destroy_workqueue() rescuer->task
destroy_workqueue()
kthread_stop(rescuer->task)
rescuer_thread()
if (should_stop) {
__set_current_state(TASK_RUNNING);
set_pf_worker(false);
mutex_lock(&wq_pool_attach_mutex);
current->flags &= ~PF_WQ_WORKER;
mutex_unlock(&wq_pool_attach_mutex);
return 0;
}
kfree(rescuer)
wq_worker_comm() would acquire wq_pool_attach_mutex then check if task->flags
is set PF_WQ_WORKER.
If PF_WQ_WORKER is not set, wq_worker_comm() would not access this task's worker
any more;
If PF_WQ_WORKER is set, the wq_pool_attach_mutex is held durning access of task's
worker.
What confuse me mostly is why the origin logic only append worker's desc when
worker is attached to a work pool.
Thinks.
>
> Kind regards,
>
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