fuse: {io-uring} Handle teardown of ring entries

On teardown struct file_operations::uring_cmd requests
need to be completed by calling io_uring_cmd_done().
Not completing all ring entries would result in busy io-uring
tasks giving warning messages in intervals and unreleased
struct file.

Additionally the fuse connection and with that the ring can
only get released when all io-uring commands are completed.

Completion is done with ring entries that are
a) in waiting state for new fuse requests - io_uring_cmd_done
is needed

b) already in userspace - io_uring_cmd_done through teardown
is not needed, the request can just get released. If fuse server
is still active and commits such a ring entry, fuse_uring_cmd()
already checks if the connection is active and then complete the
io-uring itself with -ENOTCONN. I.e. special handling is not
needed.

This scheme is basically represented by the ring entry state
FRRS_WAIT and FRRS_USERSPACE.

Entries in state:
- FRRS_INIT: No action needed, do not contribute to
  ring->queue_refs yet
- All other states: Are currently processed by other tasks,
  async teardown is needed and it has to wait for the two
  states above. It could be also solved without an async
  teardown task, but would require additional if conditions
  in hot code paths. Also in my personal opinion the code
  looks cleaner with async teardown.

Signed-off-by: Bernd Schubert <bschubert@ddn.com>
Reviewed-by: Pavel Begunkov <asml.silence@gmail.com> # io_uring
Reviewed-by: Luis Henriques <luis@igalia.com>
Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>

1 files changed, 207 insertions, 0 deletions

diff --git a/fs/fuse/dev_uring.c b/fs/fuse/dev_uring.c
index 1030c1720990..1161b9aa5e11 100644
--- a/fs/fuse/dev_uring.c
+++ b/fs/fuse/dev_uring.c
@@ -35,6 +35,37 @@ static void fuse_uring_req_end(struct fuse_ring_ent *ent, struct fuse_req *req,
 	fuse_request_end(req);
 }
 
+/* Abort all list queued request on the given ring queue */
+static void fuse_uring_abort_end_queue_requests(struct fuse_ring_queue *queue)
+{
+	struct fuse_req *req;
+	LIST_HEAD(req_list);
+
+	spin_lock(&queue->lock);
+	list_for_each_entry(req, &queue->fuse_req_queue, list)
+		clear_bit(FR_PENDING, &req->flags);
+	list_splice_init(&queue->fuse_req_queue, &req_list);
+	spin_unlock(&queue->lock);
+
+	/* must not hold queue lock to avoid order issues with fi->lock */
+	fuse_dev_end_requests(&req_list);
+}
+
+void fuse_uring_abort_end_requests(struct fuse_ring *ring)
+{
+	int qid;
+	struct fuse_ring_queue *queue;
+
+	for (qid = 0; qid < ring->nr_queues; qid++) {
+		queue = READ_ONCE(ring->queues[qid]);
+		if (!queue)
+			continue;
+
+		queue->stopped = true;
+		fuse_uring_abort_end_queue_requests(queue);
+	}
+}
+
 void fuse_uring_destruct(struct fuse_conn *fc)
 {
 	struct fuse_ring *ring = fc->ring;
@@ -94,10 +125,13 @@ static struct fuse_ring *fuse_uring_create(struct fuse_conn *fc)
 		goto out_err;
 	}
 
+	init_waitqueue_head(&ring->stop_waitq);
+
 	fc->ring = ring;
 	ring->nr_queues = nr_queues;
 	ring->fc = fc;
 	ring->max_payload_sz = max_payload_size;
+	atomic_set(&ring->queue_refs, 0);
 
 	spin_unlock(&fc->lock);
 	return ring;
@@ -154,6 +188,175 @@ static struct fuse_ring_queue *fuse_uring_create_queue(struct fuse_ring *ring,
 	return queue;
 }
 
+static void fuse_uring_stop_fuse_req_end(struct fuse_req *req)
+{
+	clear_bit(FR_SENT, &req->flags);
+	req->out.h.error = -ECONNABORTED;
+	fuse_request_end(req);
+}
+
+/*
+ * Release a request/entry on connection tear down
+ */
+static void fuse_uring_entry_teardown(struct fuse_ring_ent *ent)
+{
+	struct fuse_req *req;
+	struct io_uring_cmd *cmd;
+
+	struct fuse_ring_queue *queue = ent->queue;
+
+	spin_lock(&queue->lock);
+	cmd = ent->cmd;
+	ent->cmd = NULL;
+	req = ent->fuse_req;
+	ent->fuse_req = NULL;
+	if (req) {
+		/* remove entry from queue->fpq->processing */
+		list_del_init(&req->list);
+	}
+	spin_unlock(&queue->lock);
+
+	if (cmd)
+		io_uring_cmd_done(cmd, -ENOTCONN, 0, IO_URING_F_UNLOCKED);
+
+	if (req)
+		fuse_uring_stop_fuse_req_end(req);
+
+	list_del_init(&ent->list);
+	kfree(ent);
+}
+
+static void fuse_uring_stop_list_entries(struct list_head *head,
+					 struct fuse_ring_queue *queue,
+					 enum fuse_ring_req_state exp_state)
+{
+	struct fuse_ring *ring = queue->ring;
+	struct fuse_ring_ent *ent, *next;
+	ssize_t queue_refs = SSIZE_MAX;
+	LIST_HEAD(to_teardown);
+
+	spin_lock(&queue->lock);
+	list_for_each_entry_safe(ent, next, head, list) {
+		if (ent->state != exp_state) {
+			pr_warn("entry teardown qid=%d state=%d expected=%d",
+				queue->qid, ent->state, exp_state);
+			continue;
+		}
+
+		list_move(&ent->list, &to_teardown);
+	}
+	spin_unlock(&queue->lock);
+
+	/* no queue lock to avoid lock order issues */
+	list_for_each_entry_safe(ent, next, &to_teardown, list) {
+		fuse_uring_entry_teardown(ent);
+		queue_refs = atomic_dec_return(&ring->queue_refs);
+		WARN_ON_ONCE(queue_refs < 0);
+	}
+}
+
+static void fuse_uring_teardown_entries(struct fuse_ring_queue *queue)
+{
+	fuse_uring_stop_list_entries(&queue->ent_in_userspace, queue,
+				     FRRS_USERSPACE);
+	fuse_uring_stop_list_entries(&queue->ent_avail_queue, queue,
+				     FRRS_AVAILABLE);
+}
+
+/*
+ * Log state debug info
+ */
+static void fuse_uring_log_ent_state(struct fuse_ring *ring)
+{
+	int qid;
+	struct fuse_ring_ent *ent;
+
+	for (qid = 0; qid < ring->nr_queues; qid++) {
+		struct fuse_ring_queue *queue = ring->queues[qid];
+
+		if (!queue)
+			continue;
+
+		spin_lock(&queue->lock);
+		/*
+		 * Log entries from the intermediate queue, the other queues
+		 * should be empty
+		 */
+		list_for_each_entry(ent, &queue->ent_w_req_queue, list) {
+			pr_info(" ent-req-queue ring=%p qid=%d ent=%p state=%d\n",
+				ring, qid, ent, ent->state);
+		}
+		list_for_each_entry(ent, &queue->ent_commit_queue, list) {
+			pr_info(" ent-commit-queue ring=%p qid=%d ent=%p state=%d\n",
+				ring, qid, ent, ent->state);
+		}
+		spin_unlock(&queue->lock);
+	}
+	ring->stop_debug_log = 1;
+}
+
+static void fuse_uring_async_stop_queues(struct work_struct *work)
+{
+	int qid;
+	struct fuse_ring *ring =
+		container_of(work, struct fuse_ring, async_teardown_work.work);
+
+	/* XXX code dup */
+	for (qid = 0; qid < ring->nr_queues; qid++) {
+		struct fuse_ring_queue *queue = READ_ONCE(ring->queues[qid]);
+
+		if (!queue)
+			continue;
+
+		fuse_uring_teardown_entries(queue);
+	}
+
+	/*
+	 * Some ring entries might be in the middle of IO operations,
+	 * i.e. in process to get handled by file_operations::uring_cmd
+	 * or on the way to userspace - we could handle that with conditions in
+	 * run time code, but easier/cleaner to have an async tear down handler
+	 * If there are still queue references left
+	 */
+	if (atomic_read(&ring->queue_refs) > 0) {
+		if (time_after(jiffies,
+			       ring->teardown_time + FUSE_URING_TEARDOWN_TIMEOUT))
+			fuse_uring_log_ent_state(ring);
+
+		schedule_delayed_work(&ring->async_teardown_work,
+				      FUSE_URING_TEARDOWN_INTERVAL);
+	} else {
+		wake_up_all(&ring->stop_waitq);
+	}
+}
+
+/*
+ * Stop the ring queues
+ */
+void fuse_uring_stop_queues(struct fuse_ring *ring)
+{
+	int qid;
+
+	for (qid = 0; qid < ring->nr_queues; qid++) {
+		struct fuse_ring_queue *queue = READ_ONCE(ring->queues[qid]);
+
+		if (!queue)
+			continue;
+
+		fuse_uring_teardown_entries(queue);
+	}
+
+	if (atomic_read(&ring->queue_refs) > 0) {
+		ring->teardown_time = jiffies;
+		INIT_DELAYED_WORK(&ring->async_teardown_work,
+				  fuse_uring_async_stop_queues);
+		schedule_delayed_work(&ring->async_teardown_work,
+				      FUSE_URING_TEARDOWN_INTERVAL);
+	} else {
+		wake_up_all(&ring->stop_waitq);
+	}
+}
+
 /*
  * Checks for errors and stores it into the request
  */
@@ -525,6 +728,9 @@ static int fuse_uring_commit_fetch(struct io_uring_cmd *cmd, int issue_flags,
 		return err;
 	fpq = &queue->fpq;
 
+	if (!READ_ONCE(fc->connected) || READ_ONCE(queue->stopped))
+		return err;
+
 	spin_lock(&queue->lock);
 	/* Find a request based on the unique ID of the fuse request
 	 * This should get revised, as it needs a hash calculation and list
@@ -652,6 +858,7 @@ fuse_uring_create_ring_ent(struct io_uring_cmd *cmd,
 	ent->headers = iov[0].iov_base;
 	ent->payload = iov[1].iov_base;
 
+	atomic_inc(&ring->queue_refs);
 	return ent;
 }