io_uring: fix short read retries for non-reg files

ANBZ: torvalds#190

commit 9a17334 upstream.

Sockets and other non-regular files may actually expect short reads to
happen, don't retry reads for them. Because non-reg files don't set
FMODE_BUF_RASYNC and so it won't do second/retry do_read, we can filter
out those cases after first do_read() attempt with ret>0.

Cc: [email protected] # 5.9+
Suggested-by: Jens Axboe <[email protected]>
Signed-off-by: Pavel Begunkov <[email protected]>
Signed-off-by: Jens Axboe <[email protected]>
Signed-off-by: Joseph Qi <[email protected]>
Reviewed-by: Xiaoguang Wang <[email protected]>
Reviewed-by: Hao Xu <[email protected]>
Tested-by: Hao Xu <[email protected]>

fs/io_uring.c

@@ -3109,7 +3109,7 @@ static int io_read(struct io_kiocb *req, bool force_nonblock)
 
 	/* read it all, or we did blocking attempt. no retry. */
 	if (!iov_iter_count(iter) || !force_nonblock ||
-	    (req->file->f_flags & O_NONBLOCK))
+	    (req->file->f_flags & O_NONBLOCK) || !(req->flags & REQ_F_ISREG))
 		goto done;
 
 	io_size -= ret;