workqueue: Warn when a rescuer could not be created

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().

Signed-off-by: Petr Mladek <pmladek@suse.com>
Signed-off-by: Tejun Heo <tj@kernel.org>

diff --git a/kernel/workqueue.c b/kernel/workqueue.c
index 5f0ecaaaf99776fc33ad21661d9bc7d09d6d5116..fb1eb7a3f49b28b26c12ba2c0bf5b2507c98595e 100644 (file)
--- a/kernel/workqueue.c
+++ b/kernel/workqueue.c
@@ -4391,13 +4391,18 @@ static int init_rescuer(struct workqueue_struct *wq)
                return 0;
 
        rescuer = alloc_worker(NUMA_NO_NODE);
-       if (!rescuer)
+       if (!rescuer) {
+               pr_err("workqueue: Failed to allocate a rescuer for wq \"%s\"\n",
+                      wq->name);
                return -ENOMEM;
+       }
 
        rescuer->rescue_wq = wq;
        rescuer->task = kthread_create(rescuer_thread, rescuer, "%s", wq->name);
        if (IS_ERR(rescuer->task)) {
                ret = PTR_ERR(rescuer->task);
+               pr_err("workqueue: Failed to create a rescuer kthread for wq \"%s\": %pe",
+                      wq->name, ERR_PTR(ret));
                kfree(rescuer);
                return ret;
        }