[PATCH 1/2] io_uring: wait potential ->release() on resurrect

[Pavel Begunkov <asml.silence@gmail.com>]

There is a short window where percpu_refs are already turned zero, but
we try to do resurrect(). Play nicer and wait for all users to leave RCU
section.

Cc: <stable@vger.kernel.org> # 5.5+
Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
---
 fs/io_uring.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/fs/io_uring.c b/fs/io_uring.c
index f3af499b12a9..ce5fccf00367 100644
--- a/fs/io_uring.c
+++ b/fs/io_uring.c
@@ -7351,6 +7351,7 @@ static int io_rsrc_ref_quiesce(struct fixed_rsrc_data *data,
 			break;
 
 		percpu_ref_resurrect(&data->refs);
+		synchronize_rcu();
 		io_sqe_rsrc_set_node(ctx, data, backup_node);
 		reinit_completion(&data->done);
 		mutex_unlock(&ctx->uring_lock);
@@ -10089,6 +10090,7 @@ static int __io_uring_register(struct io_ring_ctx *ctx, unsigned opcode,
 
 		if (ret) {
 			percpu_ref_resurrect(&ctx->refs);
+			synchronize_rcu();
 			goto out_quiesce;
 		}
 	}
-- 
2.24.0