workqueue: introduce numa_pwq_tbl_install()

Factor out pool_workqueue linking and installation into numa_pwq_tbl[]
from apply_workqueue_attrs() into numa_pwq_tbl_install().  link_pwq()
is made safe to call multiple times.  numa_pwq_tbl_install() links the
pwq, installs it into numa_pwq_tbl[] at the specified node and returns
the old entry.

@last_pwq is removed from link_pwq() as the return value of the new
function can be used instead.

This is to prepare for NUMA affinity support for unbound workqueues.

Signed-off-by: Tejun Heo <tj@kernel.org>
Reviewed-by: Lai Jiangshan <laijs@cn.fujitsu.com>

1 files changed, 26 insertions, 9 deletions

diff --git a/kernel/workqueue.c b/kernel/workqueue.c
index 07ec57459457..3825c14304e1 100644
--- a/kernel/workqueue.c
+++ b/kernel/workqueue.c
@@ -3639,24 +3639,26 @@ static void init_pwq(struct pool_workqueue *pwq, struct workqueue_struct *wq,
         pwq->flush_color = -1;
         pwq->refcnt = 1;
         INIT_LIST_HEAD(&pwq->delayed_works);
+        INIT_LIST_HEAD(&pwq->pwqs_node);
         INIT_LIST_HEAD(&pwq->mayday_node);
         INIT_WORK(&pwq->unbound_release_work, pwq_unbound_release_workfn);
 }
 
 /* sync @pwq with the current state of its associated wq and link it */
-static void link_pwq(struct pool_workqueue *pwq,
-                     struct pool_workqueue **p_last_pwq)
+static void link_pwq(struct pool_workqueue *pwq)
 {
         struct workqueue_struct *wq = pwq->wq;
 
         lockdep_assert_held(&wq->mutex);
 
+        /* may be called multiple times, ignore if already linked */
+        if (!list_empty(&pwq->pwqs_node))
+                return;
+
         /*
          * Set the matching work_color.  This is synchronized with
          * wq->mutex to avoid confusing flush_workqueue().
          */
-        if (p_last_pwq)
-                *p_last_pwq = first_pwq(wq);
         pwq->work_color = wq->work_color;
 
         /* sync max_active to the current setting */
@@ -3689,6 +3691,23 @@ static struct pool_workqueue *alloc_unbound_pwq(struct workqueue_struct *wq,
         return pwq;
 }
 
+/* install @pwq into @wq's numa_pwq_tbl[] for @node and return the old pwq */
+static struct pool_workqueue *numa_pwq_tbl_install(struct workqueue_struct *wq,
+                                                   int node,
+                                                   struct pool_workqueue *pwq)
+{
+        struct pool_workqueue *old_pwq;
+
+        lockdep_assert_held(&wq->mutex);
+
+        /* link_pwq() can handle duplicate calls */
+        link_pwq(pwq);
+
+        old_pwq = rcu_access_pointer(wq->numa_pwq_tbl[node]);
+        rcu_assign_pointer(wq->numa_pwq_tbl[node], pwq);
+        return old_pwq;
+}
+
 /**
  * apply_workqueue_attrs - apply new workqueue_attrs to an unbound workqueue
  * @wq: the target workqueue
@@ -3707,7 +3726,7 @@ int apply_workqueue_attrs(struct workqueue_struct *wq,
                           const struct workqueue_attrs *attrs)
 {
         struct workqueue_attrs *new_attrs;
-        struct pool_workqueue *pwq, *last_pwq;
+        struct pool_workqueue *pwq, *last_pwq = NULL;
         int node, ret;
 
         /* only unbound workqueues can change attributes */
@@ -3734,11 +3753,9 @@ int apply_workqueue_attrs(struct workqueue_struct *wq,
 
         mutex_lock(&wq->mutex);
 
-        link_pwq(pwq, &last_pwq);
-
         copy_workqueue_attrs(wq->unbound_attrs, new_attrs);
         for_each_node(node)
-                rcu_assign_pointer(wq->numa_pwq_tbl[node], pwq);
+                last_pwq = numa_pwq_tbl_install(wq, node, pwq);
 
         mutex_unlock(&wq->mutex);
 
@@ -3778,7 +3795,7 @@ static int alloc_and_link_pwqs(struct workqueue_struct *wq)
                         init_pwq(pwq, wq, &cpu_pools[highpri]);
 
                         mutex_lock(&wq->mutex);
-                        link_pwq(pwq, NULL);
+                        link_pwq(pwq);
                         mutex_unlock(&wq->mutex);
                 }
                 return 0;