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Subject[PATCH wq/for-5.4-fixes] workqueue: more destroy_workqueue() fixes
From c29eb85386880750130a01aabf288408a6614d65 Mon Sep 17 00:00:00 2001
From: Tejun Heo <tj@kernel.org>
Date: Mon, 23 Sep 2019 11:08:58 -0700
Subject: [PATCH] workqueue: more destroy_workqueue() fixes

destroy_workqueue() warnings still, at a lower frequency, trigger
spuriously. The problem seems to be in-flight operations which
haven't reached put_pwq() yet.

* Make sanity check grab all the related locks so that it's
synchronized against operations which puts pwq at the end.

* Always print out the offending pwq.

Signed-off-by: Tejun Heo <tj@kernel.org>
Cc: "Williams, Gerald S" <gerald.s.williams@intel.com>
---
Applying to wq/for-5.4-fixes to plug the remaining holes during
destruction sanity checks.

Thanks.

kernel/workqueue.c | 45 +++++++++++++++++++++++++++++++--------------
1 file changed, 31 insertions(+), 14 deletions(-)

diff --git a/kernel/workqueue.c b/kernel/workqueue.c
index 7f7aa45dac37..4a3c30177b94 100644
--- a/kernel/workqueue.c
+++ b/kernel/workqueue.c
@@ -355,6 +355,7 @@ EXPORT_SYMBOL_GPL(system_freezable_power_efficient_wq);

static int worker_thread(void *__worker);
static void workqueue_sysfs_unregister(struct workqueue_struct *wq);
+static void show_pwq(struct pool_workqueue *pwq);

#define CREATE_TRACE_POINTS
#include <trace/events/workqueue.h>
@@ -4314,6 +4315,22 @@ struct workqueue_struct *alloc_workqueue(const char *fmt,
}
EXPORT_SYMBOL_GPL(alloc_workqueue);

+static bool pwq_busy(struct pool_workqueue *pwq)
+{
+ int i;
+
+ for (i = 0; i < WORK_NR_COLORS; i++)
+ if (pwq->nr_in_flight[i])
+ return true;
+
+ if ((pwq != pwq->wq->dfl_pwq) && (pwq->refcnt > 1))
+ return true;
+ if (pwq->nr_active || !list_empty(&pwq->delayed_works))
+ return true;
+
+ return false;
+}
+
/**
* destroy_workqueue - safely terminate a workqueue
* @wq: target workqueue
@@ -4348,28 +4365,28 @@ void destroy_workqueue(struct workqueue_struct *wq)
kfree(rescuer);
}

- /* sanity checks */
+ /*
+ * Sanity checks - grab all the locks so that we wait for all
+ * in-flight operations which may do put_pwq().
+ */
+ mutex_lock(&wq_pool_mutex);
mutex_lock(&wq->mutex);
for_each_pwq(pwq, wq) {
- int i;
-
- for (i = 0; i < WORK_NR_COLORS; i++) {
- if (WARN_ON(pwq->nr_in_flight[i])) {
- mutex_unlock(&wq->mutex);
- show_workqueue_state();
- return;
- }
- }
-
- if (WARN_ON((pwq != wq->dfl_pwq) && (pwq->refcnt > 1)) ||
- WARN_ON(pwq->nr_active) ||
- WARN_ON(!list_empty(&pwq->delayed_works))) {
+ spin_lock_irq(&pwq->pool->lock);
+ if (WARN_ON(pwq_busy(pwq))) {
+ pr_warning("%s: %s has the following busy pwq (refcnt=%d)\n",
+ __func__, wq->name, pwq->refcnt);
+ show_pwq(pwq);
+ spin_unlock_irq(&pwq->pool->lock);
mutex_unlock(&wq->mutex);
+ mutex_unlock(&wq_pool_mutex);
show_workqueue_state();
return;
}
+ spin_unlock_irq(&pwq->pool->lock);
}
mutex_unlock(&wq->mutex);
+ mutex_unlock(&wq_pool_mutex);

/*
* wq list is used to freeze wq, remove from list after
--
2.17.1
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