io_uring: ensure fput() called correspondingly when direct install fails

io_fixed_fd_install() may fail for short of free fixed file bitmap,
in this case, need to call fput() correspondingly.
Signed-off-by: Xiaoguang Wang <xiaoguang.wang@linux.alibaba.com>
Link: https://lore.kernel.org/r/20220527025400.51048-1-xiaoguang.wang@linux.alibaba.comSigned-off-by: Jens Axboe <axboe@kernel.dk>

fs/io_uring.c

@@ -5438,6 +5438,10 @@ static int io_file_bitmap_get(struct io_ring_ctx *ctx)
 	return -ENFILE;
 }
 
+/*
+ * Note when io_fixed_fd_install() returns error value, it will ensure
+ * fput() is called correspondingly.
+ */
 static int io_fixed_fd_install(struct io_kiocb *req, unsigned int issue_flags,
 			       struct file *file, unsigned int file_slot)
 {
@@ -5450,6 +5454,7 @@ static int io_fixed_fd_install(struct io_kiocb *req, unsigned int issue_flags,
 		ret = io_file_bitmap_get(ctx);
 		if (unlikely(ret < 0)) {
 			io_ring_submit_unlock(ctx, issue_flags);
+			fput(file);
 			return ret;
 		}