io_uring: account fixed file references correctly in batch

to #26323588

commit 10fef4bebf979bb705feed087611293d5864adfe upstream.

We can't assume that the whole batch has fixed files in it. If it's a
mix, or none at all, then we can end up doing a ref put that either
messes up accounting, or causes an oops if we have no fixed files at
all.

Also ensure we free requests properly between inflight accounted and
normal requests.

Fixes: 82c721577011 ("io_uring: extend batch freeing to cover more cases")
Reported-by: NDmitrii Dolgov <9erthalion6@gmail.com>
Reported-by: NPavel Begunkov <asml.silence@gmail.com>
Tested-by: NDmitrii Dolgov <9erthalion6@gmail.com>
Signed-off-by: NJens Axboe <axboe@kernel.dk>
Signed-off-by: NJoseph Qi <joseph.qi@linux.alibaba.com>
Acked-by: NXiaoguang Wang <xiaoguang.wang@linux.alibaba.com>

fs/io_uring.c

@@ -1207,21 +1207,24 @@ struct req_batch {
 
 static void io_free_req_many(struct io_ring_ctx *ctx, struct req_batch *rb)
 {
+	int fixed_refs = rb->to_free;
+
 	if (!rb->to_free)
 		return;
 	if (rb->need_iter) {
 		int i, inflight = 0;
 		unsigned long flags;
 
+		fixed_refs = 0;
 		for (i = 0; i < rb->to_free; i++) {
 			struct io_kiocb *req = rb->reqs[i];
 
-			if (req->flags & REQ_F_FIXED_FILE)
+			if (req->flags & REQ_F_FIXED_FILE) {
 				req->file = NULL;
+				fixed_refs++;
+			}
 			if (req->flags & REQ_F_INFLIGHT)
 				inflight++;
-			else
-				rb->reqs[i] = NULL;
 			__io_req_aux_free(req);
 		}
 		if (!inflight)
@@ -1231,7 +1234,7 @@ static void io_free_req_many(struct io_ring_ctx *ctx, struct req_batch *rb)
 		for (i = 0; i < rb->to_free; i++) {
 			struct io_kiocb *req = rb->reqs[i];
 
-			if (req) {
+			if (req->flags & REQ_F_INFLIGHT) {
 				list_del(&req->inflight_entry);
 				if (!--inflight)
 					break;
@@ -1244,8 +1247,9 @@ static void io_free_req_many(struct io_ring_ctx *ctx, struct req_batch *rb)
 	}
 do_free:
 	kmem_cache_free_bulk(req_cachep, rb->to_free, rb->reqs);
+	if (fixed_refs)
+		percpu_ref_put_many(&ctx->file_data->refs, fixed_refs);
 	percpu_ref_put_many(&ctx->refs, rb->to_free);
-	percpu_ref_put_many(&ctx->file_data->refs, rb->to_free);
 	rb->to_free = rb->need_iter = 0;
 }