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Subject[PATCH 25/31] workqueue: perform non-reentrancy test when queueing to unbound workqueues too
Date
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>
---
kernel/workqueue.c | 42 +++++++++++++++++++-----------------------
1 file changed, 19 insertions(+), 23 deletions(-)

diff --git a/kernel/workqueue.c b/kernel/workqueue.c
index 0f0da59..4c67967 100644
--- a/kernel/workqueue.c
+++ b/kernel/workqueue.c
@@ -1206,6 +1206,7 @@ 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;
@@ -1225,41 +1226,36 @@ 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);
}

--
1.8.1.2


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