[PATCH 3/4] io-wq: allow lookup of existing io_wq with given id

[Jens Axboe <axboe@kernel.dk>]

If the id and user/creds match, return an existing io_wq if we can safely
grab a reference to it.

Signed-off-by: Jens Axboe <axboe@kernel.dk>
---
 fs/io-wq.c | 42 +++++++++++++++++++++++++++++++++++++++++-
 fs/io-wq.h |  3 +++
 2 files changed, 44 insertions(+), 1 deletion(-)

diff --git a/fs/io-wq.c b/fs/io-wq.c
index 8cb0cff5f15c..a9985856033d 100644
--- a/fs/io-wq.c
+++ b/fs/io-wq.c
@@ -1024,7 +1024,7 @@ void io_wq_flush(struct io_wq *wq)
 	}
 }
 
-struct io_wq *io_wq_create(unsigned bounded, struct io_wq_data *data)
+static struct io_wq *__io_wq_create(unsigned bounded, struct io_wq_data *data)
 {
 	int ret = -ENOMEM, node, id;
 	struct io_wq *wq;
@@ -1107,6 +1107,41 @@ struct io_wq *io_wq_create(unsigned bounded, struct io_wq_data *data)
 	return ERR_PTR(ret);
 }
 
+struct io_wq *io_wq_create(unsigned bounded, struct io_wq_data *data)
+{
+	return __io_wq_create(bounded, data);
+}
+
+/*
+ * Find and return io_wq with given id and grab a reference to it.
+ */
+struct io_wq *io_wq_create_id(unsigned bounded, struct io_wq_data *data,
+			      unsigned int id)
+{
+	struct io_wq *wq, *ret = NULL;
+
+	mutex_lock(&wq_lock);
+	list_for_each_entry(wq, &wq_list, wq_list) {
+		if (id != wq->id)
+			continue;
+		if (data->creds != wq->creds || data->user != wq->user)
+			continue;
+		if (data->get_work != wq->get_work ||
+		    data->put_work != wq->put_work)
+			continue;
+		if (!refcount_inc_not_zero(&wq->use_refs))
+			continue;
+		ret = wq;
+		break;
+	}
+	mutex_unlock(&wq_lock);
+
+	if (!ret)
+		ret = io_wq_create(bounded, data);
+
+	return ret;
+}
+
 static bool io_wq_worker_wake(struct io_worker *worker, void *data)
 {
 	wake_up_process(worker->task);
@@ -1145,3 +1180,8 @@ void io_wq_destroy(struct io_wq *wq)
 		__io_wq_destroy(wq);
 	}
 }
+
+unsigned int io_wq_id(struct io_wq *wq)
+{
+	return wq->id;
+}
diff --git a/fs/io-wq.h b/fs/io-wq.h
index 1cd039af8813..7abe2c56b535 100644
--- a/fs/io-wq.h
+++ b/fs/io-wq.h
@@ -98,7 +98,10 @@ struct io_wq_data {
 };
 
 struct io_wq *io_wq_create(unsigned bounded, struct io_wq_data *data);
+struct io_wq *io_wq_create_id(unsigned bounded, struct io_wq_data *data,
+				unsigned int id);
 void io_wq_destroy(struct io_wq *wq);
+unsigned int io_wq_id(struct io_wq *wq);
 
 void io_wq_enqueue(struct io_wq *wq, struct io_wq_work *work);
 void io_wq_enqueue_hashed(struct io_wq *wq, struct io_wq_work *work, void *val);
-- 
2.25.0