[PATCH for-next 1/7] io_uring: add completion locking for iopoll

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

There are pieces of code that may allow iopoll to race filling cqes,
temporarily add spinlocking around posting events.

Cc: stable@vger.kernel.org
Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
---
 io_uring/rw.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/io_uring/rw.c b/io_uring/rw.c
index 1ce065709724..61c326831949 100644
--- a/io_uring/rw.c
+++ b/io_uring/rw.c
@@ -1049,6 +1049,7 @@ int io_do_iopoll(struct io_ring_ctx *ctx, bool force_nonspin)
 	else if (!pos)
 		return 0;
 
+	spin_lock(&ctx->completion_lock);
 	prev = start;
 	wq_list_for_each_resume(pos, prev) {
 		struct io_kiocb *req = container_of(pos, struct io_kiocb, comp_list);
@@ -1063,11 +1064,11 @@ int io_do_iopoll(struct io_ring_ctx *ctx, bool force_nonspin)
 		req->cqe.flags = io_put_kbuf(req, 0);
 		__io_fill_cqe_req(req->ctx, req);
 	}
-
+	io_commit_cqring(ctx);
+	spin_unlock(&ctx->completion_lock);
 	if (unlikely(!nr_events))
 		return 0;
 
-	io_commit_cqring(ctx);
 	io_cqring_ev_posted_iopoll(ctx);
 	pos = start ? start->next : ctx->iopoll_list.first;
 	wq_list_cut(&ctx->iopoll_list, prev, start);
-- 
2.38.1