workqueue: Show the latest workqueue name in /proc/PID/{comm,stat,status}

There can be a lot of workqueue workers and they all show up with the
cryptic kworker/* names making it difficult to understand which is
doing what and how they came to be.

  # ps -ef | grep kworker
  root           4       2  0 Feb25 ?        00:00:00 [kworker/0:0H]
  root           6       2  0 Feb25 ?        00:00:00 [kworker/u112:0]
  root          19       2  0 Feb25 ?        00:00:00 [kworker/1:0H]
  root          25       2  0 Feb25 ?        00:00:00 [kworker/2:0H]
  root          31       2  0 Feb25 ?        00:00:00 [kworker/3:0H]
  ...

This patch makes workqueue workers report the latest workqueue it was
executing for through /proc/PID/{comm,stat,status}.  The extra
information is appended to the kthread name with intervening '+' if
currently executing, otherwise '-'.

  # cat /proc/25/comm
  kworker/2:0-events_power_efficient
  # cat /proc/25/stat
  25 (kworker/2:0-events_power_efficient) I 2 0 0 0 -1 69238880 0 0...
  # grep Name /proc/25/status
  Name:   kworker/2:0-events_power_efficient

Unfortunately, ps(1) truncates comm to 15 characters,

  # ps 25
    PID TTY      STAT   TIME COMMAND
     25 ?        I      0:00 [kworker/2:0-eve]

making it a lot less useful; however, this should be an easy fix from
ps(1) side.

Signed-off-by: Tejun Heo <tj@kernel.org>
Suggested-by: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Craig Small <csmall@enc.com.au>

diff --git a/fs/proc/array.c b/fs/proc/array.c
index f29221e9579255269cd8b5801d3d5dc10ca55ff2..bb1d3619ca12dec0762c9546103ca8937c9aeb3c 100644 (file)
--- a/fs/proc/array.c
+++ b/fs/proc/array.c
@@ -99,10 +99,13 @@ void proc_task_name(struct seq_file *m, struct task_struct *p, bool escape)
 {
        char *buf;
        size_t size;
-       char tcomm[sizeof(p->comm)];
+       char tcomm[64];
        int ret;
 
-       get_task_comm(tcomm, p);
+       if (p->flags & PF_WQ_WORKER)
+               wq_worker_comm(tcomm, sizeof(tcomm), p);
+       else
+               __get_task_comm(tcomm, sizeof(tcomm), p);
 
        size = seq_get_buf(m, &buf);
        if (escape) {

diff --git a/include/linux/workqueue.h b/include/linux/workqueue.h
index 39a0e215022a458e21ed57af697ba8e544510bfc..60d673e15632126a038b1efe12108abe122fc235 100644 (file)
--- a/include/linux/workqueue.h
+++ b/include/linux/workqueue.h
@@ -494,6 +494,7 @@ extern unsigned int work_busy(struct work_struct *work);
 extern __printf(1, 2) void set_worker_desc(const char *fmt, ...);
 extern void print_worker_info(const char *log_lvl, struct task_struct *task);
 extern void show_workqueue_state(void);
+extern void wq_worker_comm(char *buf, size_t size, struct task_struct *task);
 
 /**
  * queue_work - queue work on a workqueue

diff --git a/kernel/workqueue.c b/kernel/workqueue.c
index 3fbe0076492c4bb1117d414f6d4ab9980a20c578..b4a39a15c931caae2dfbafbb72b852a01ee04e60 100644 (file)
--- a/kernel/workqueue.c
+++ b/kernel/workqueue.c
@@ -4577,6 +4577,45 @@ void show_workqueue_state(void)
        rcu_read_unlock_sched();
 }
 
+/* used to show worker information through /proc/PID/{comm,stat,status} */
+void wq_worker_comm(char *buf, size_t size, struct task_struct *task)
+{
+       struct worker *worker;
+       struct worker_pool *pool;
+       int off;
+
+       /* always show the actual comm */
+       off = strscpy(buf, task->comm, size);
+       if (off < 0)
+               return;
+
+       /* stabilize worker pool association */
+       mutex_lock(&wq_pool_attach_mutex);
+
+       worker = kthread_data(task);
+       pool = worker->pool;
+
+       if (pool) {
+               spin_lock_irq(&pool->lock);
+               /*
+                * ->desc tracks information (wq name or set_worker_desc())
+                * for the latest execution.  If current, prepend '+',
+                * otherwise '-'.
+                */
+               if (worker->desc[0] != '\0') {
+                       if (worker->current_work)
+                               scnprintf(buf + off, size - off, "+%s",
+                                         worker->desc);
+                       else
+                               scnprintf(buf + off, size - off, "-%s",
+                                         worker->desc);
+               }
+               spin_unlock_irq(&pool->lock);
+       }
+
+       mutex_unlock(&wq_pool_attach_mutex);
+}
+
 /*
  * CPU hotplug.
  *