[PATCH 1/1] io_uring: disallow concurrent rsrc quiesce

[Pavel Begunkov <asml.silence@xxxxxxxxx>]

Add a flag for marking a rsrc data quiescing to disallow doing it from
several tasks concurrently.

Cc: Hao Xu <haoxu@xxxxxxxxxxxxxxxxx>
Fixes: 853a012bdbddce869561 ("io_uring: fix io_rsrc_ref_quiesce races")
Signed-off-by: Pavel Begunkov <asml.silence@xxxxxxxxx>
---
 fs/io_uring.c | 21 ++++++++++++++-------
 1 file changed, 14 insertions(+), 7 deletions(-)

diff --git a/fs/io_uring.c b/fs/io_uring.c
index f3af499b12a9..ff8f50d3cf44 100644
--- a/fs/io_uring.c
+++ b/fs/io_uring.c
@@ -236,6 +236,7 @@ struct fixed_rsrc_data {
 	struct fixed_rsrc_ref_node	*node;
 	struct percpu_ref		refs;
 	struct completion		done;
+	bool				quiesce;
 };
 
 struct io_buffer {
@@ -7335,10 +7336,15 @@ static int io_rsrc_ref_quiesce(struct fixed_rsrc_data *data,
 	struct fixed_rsrc_ref_node *backup_node;
 	int ret;
 
+	if (data->quiesce)
+		return -ENXIO;
+
+	data->quiesce = true;
 	do {
 		backup_node = alloc_fixed_rsrc_ref_node(ctx);
+		ret = -ENOMEM;
 		if (!backup_node)
-			return -ENOMEM;
+			break;
 		backup_node->rsrc_data = data;
 		backup_node->rsrc_put = rsrc_put;
 
@@ -7352,16 +7358,17 @@ static int io_rsrc_ref_quiesce(struct fixed_rsrc_data *data,
 
 		percpu_ref_resurrect(&data->refs);
 		io_sqe_rsrc_set_node(ctx, data, backup_node);
+		backup_node = NULL;
 		reinit_completion(&data->done);
 		mutex_unlock(&ctx->uring_lock);
 		ret = io_run_task_work_sig();
 		mutex_lock(&ctx->uring_lock);
-		if (ret < 0)
-			return ret;
-	} while (1);
+	} while (ret >= 0);
+	data->quiesce = false;
 
-	destroy_fixed_rsrc_ref_node(backup_node);
-	return 0;
+	if (backup_node)
+		destroy_fixed_rsrc_ref_node(backup_node);
+	return ret;
 }
 
 static struct fixed_rsrc_data *alloc_fixed_rsrc_data(struct io_ring_ctx *ctx)
@@ -7400,7 +7407,7 @@ static int io_sqe_files_unregister(struct io_ring_ctx *ctx)
 	 * Since we possibly drop uring lock later in this function to
 	 * run task work.
 	 */
-	if (!data || percpu_ref_is_dying(&data->refs))
+	if (!data)
 		return -ENXIO;
 	ret = io_rsrc_ref_quiesce(data, ctx, io_ring_file_put);
 	if (ret)
-- 
2.24.0