workqueue: perform non-reentrancy test when queueing to unbound workqueues too

Because per-cpu workqueues have multiple pwqs (pool_workqueues) to
serve the CPUs, to guarantee that a single work item isn't queued on
one pwq while still executing another, __queue_work() takes a look at
the previous pool the target work item was on and if it's still
executing there, queue the work item on that pool.

To support changing workqueue_attrs on the fly, unbound workqueues too
will have multiple pwqs and thus need non-reentrancy test when
queueing.  This patch modifies __queue_work() such that the reentrancy
test is performed regardless of the workqueue type.

per_cpu_ptr(wq->cpu_pwqs, cpu) used to be used to determine the
matching pwq for the last pool.  This can't be used for unbound
workqueues and is replaced with worker->current_pwq which also happens
to be simpler.

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

1 files changed, 19 insertions, 23 deletions

diff --git a/kernel/workqueue.c b/kernel/workqueue.c
index e933979678e5..16fb6747276a 100644
--- a/kernel/workqueue.c
+++ b/kernel/workqueue.c
@@ -1209,6 +1209,7 @@ static void __queue_work(int cpu, struct workqueue_struct *wq,
                          struct work_struct *work)
 {
         struct pool_workqueue *pwq;
+        struct worker_pool *last_pool;
         struct list_head *worklist;
         unsigned int work_flags;
         unsigned int req_cpu = cpu;
@@ -1228,41 +1229,36 @@ static void __queue_work(int cpu, struct workqueue_struct *wq,
             WARN_ON_ONCE(!is_chained_work(wq)))
                 return;
 
-        /* determine the pwq to use */
+        /* pwq which will be used unless @work is executing elsewhere */
         if (!(wq->flags & WQ_UNBOUND)) {
-                struct worker_pool *last_pool;
-
                 if (cpu == WORK_CPU_UNBOUND)
                         cpu = raw_smp_processor_id();
-
-                /*
-                 * It's multi cpu.  If @work was previously on a different
-                 * cpu, it might still be running there, in which case the
-                 * work needs to be queued on that cpu to guarantee
-                 * non-reentrancy.
-                 */
                 pwq = per_cpu_ptr(wq->cpu_pwqs, cpu);
-                last_pool = get_work_pool(work);
+        } else {
+                pwq = first_pwq(wq);
+        }
 
-                if (last_pool && last_pool != pwq->pool) {
-                        struct worker *worker;
+        /*
+         * If @work was previously on a different pool, it might still be
+         * running there, in which case the work needs to be queued on that
+         * pool to guarantee non-reentrancy.
+         */
+        last_pool = get_work_pool(work);
+        if (last_pool && last_pool != pwq->pool) {
+                struct worker *worker;
 
-                        spin_lock(&last_pool->lock);
+                spin_lock(&last_pool->lock);
 
-                        worker = find_worker_executing_work(last_pool, work);
+                worker = find_worker_executing_work(last_pool, work);
 
-                        if (worker && worker->current_pwq->wq == wq) {
-                                pwq = per_cpu_ptr(wq->cpu_pwqs, last_pool->cpu);
-                        } else {
-                                /* meh... not running there, queue here */
-                                spin_unlock(&last_pool->lock);
-                                spin_lock(&pwq->pool->lock);
-                        }
+                if (worker && worker->current_pwq->wq == wq) {
+                        pwq = worker->current_pwq;
                 } else {
+                        /* meh... not running there, queue here */
+                        spin_unlock(&last_pool->lock);
                         spin_lock(&pwq->pool->lock);
                 }
         } else {
-                pwq = first_pwq(wq);
                 spin_lock(&pwq->pool->lock);
         }