From:   Petr Mladek <pmladek@suse.com>
To:     Tejun Heo <tj@kernel.org>
Cc:     Lai Jiangshan <jiangshanlai@gmail.com>,
        Michal Koutny <mkoutny@suse.com>, linux-kernel@vger.kernel.org,
        Petr Mladek <pmladek@suse.com>
Subject: [PATCH v2 4/5] workqueue: Warn when a rescuer could not be created
Date:   Tue,  7 Mar 2023 13:53:34 +0100
Message-Id: <20230307125335.28805-5-pmladek@suse.com>
In-Reply-To: <20230307125335.28805-1-pmladek@suse.com>
References: <20230307125335.28805-1-pmladek@suse.com>
MIME-Version: 1.0
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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>
---
 kernel/workqueue.c | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/kernel/workqueue.c b/kernel/workqueue.c
index 16439d79d164..cce342defc69 100644
--- a/kernel/workqueue.c
+++ b/kernel/workqueue.c
@@ -4393,13 +4393,18 @@ 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;
 	}
-- 
2.35.3