[PATCH 3/9] workqueue: require CPU hotplug read exclusion for apply_workqueue_attrs

[Daniel Jordan]

Change the calling convention for apply_workqueue_attrs to require CPU
hotplug read exclusion.

Avoids lockdep complaints about nested calls to get_online_cpus in a
future patch where padata calls apply_workqueue_attrs when changing
other CPU-hotplug-sensitive data structures with the CPU read lock
already held.

Signed-off-by: Daniel Jordan <daniel.m.jor...@oracle.com>
Acked-by: Tejun Heo <t...@kernel.org>
Cc: Herbert Xu <herb...@gondor.apana.org.au>
Cc: Lai Jiangshan <jiangshan...@gmail.com>
Cc: Peter Zijlstra <pet...@infradead.org>
Cc: Steffen Klassert <steffen.klass...@secunet.com>
Cc: linux-crypto@vger.kernel.org
Cc: linux-ker...@vger.kernel.org
---
 kernel/workqueue.c | 19 ++++++++++++++-----
 1 file changed, 14 insertions(+), 5 deletions(-)

diff --git a/kernel/workqueue.c b/kernel/workqueue.c
index f53705ff3ff1..bc2e09a8ea61 100644
--- a/kernel/workqueue.c
+++ b/kernel/workqueue.c
@@ -4030,6 +4030,8 @@ static int apply_workqueue_attrs_locked(struct 
workqueue_struct *wq,
  *
  * Performs GFP_KERNEL allocations.
  *
+ * Assumes caller has CPU hotplug read exclusion, i.e. get_online_cpus().
+ *
  * Return: 0 on success and -errno on failure.
  */
 int apply_workqueue_attrs(struct workqueue_struct *wq,
@@ -4037,9 +4039,11 @@ int apply_workqueue_attrs(struct workqueue_struct *wq,
 {
        int ret;
 
-       apply_wqattrs_lock();
+       lockdep_assert_cpus_held();
+
+       mutex_lock(&wq_pool_mutex);
        ret = apply_workqueue_attrs_locked(wq, attrs);
-       apply_wqattrs_unlock();
+       mutex_unlock(&wq_pool_mutex);
 
        return ret;
 }
@@ -4152,16 +4156,21 @@ static int alloc_and_link_pwqs(struct workqueue_struct 
*wq)
                        mutex_unlock(&wq->mutex);
                }
                return 0;
-       } else if (wq->flags & __WQ_ORDERED) {
+       }
+
+       get_online_cpus();
+       if (wq->flags & __WQ_ORDERED) {
                ret = apply_workqueue_attrs(wq, ordered_wq_attrs[highpri]);
                /* there should only be single pwq for ordering guarantee */
                WARN(!ret && (wq->pwqs.next != &wq->dfl_pwq->pwqs_node ||
                              wq->pwqs.prev != &wq->dfl_pwq->pwqs_node),
                     "ordering guarantee broken for workqueue %s\n", wq->name);
-               return ret;
        } else {
-               return apply_workqueue_attrs(wq, unbound_std_wq_attrs[highpri]);
+               ret = apply_workqueue_attrs(wq, unbound_std_wq_attrs[highpri]);
        }
+       put_online_cpus();
+
+       return ret;
 }
 
 static int wq_clamp_max_active(int max_active, unsigned int flags,
-- 
2.22.0