From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 945BFC433F5 for ; Thu, 19 May 2022 23:12:22 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S245746AbiESXMT (ORCPT ); Thu, 19 May 2022 19:12:19 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:51608 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1343504AbiESXMO (ORCPT ); Thu, 19 May 2022 19:12:14 -0400 Received: from dfw.source.kernel.org (dfw.source.kernel.org [IPv6:2604:1380:4641:c500::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 984D31053F2 for ; Thu, 19 May 2022 16:12:10 -0700 (PDT) Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by dfw.source.kernel.org (Postfix) with ESMTPS id 3235761888 for ; Thu, 19 May 2022 23:12:10 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id EF2B1C36AF5; Thu, 19 May 2022 23:12:08 +0000 (UTC) Authentication-Results: smtp.kernel.org; dkim=pass (1024-bit key) header.d=zx2c4.com header.i=@zx2c4.com header.b="DE7K6Whm" DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=zx2c4.com; s=20210105; t=1653001927; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=VdrDpD0tLfl85nsklXAWL6SMKzi5GMiDFp0ijEM7df8=; b=DE7K6Whmj3mBtJ0YWsVxGXufXavxq55vjTRKit4nDgbWdOVTFZtYOIr+yC7V3jU+ZEJ54/ oYKkFYQYTT7W4bkWmDhGn+AflydbJCeKZwpNCedylXCEWx6Z7SALPMnaJ6USi5NV39VZE0 fbvhTGkar+8qHQdsaEBhHUQ5nY/wXyE= Received: by mail.zx2c4.com (ZX2C4 Mail Server) with ESMTPSA id f3cafe43 (TLSv1.3:AEAD-AES256-GCM-SHA384:256:NO); Thu, 19 May 2022 23:12:06 +0000 (UTC) Date: Fri, 20 May 2022 01:12:04 +0200 From: "Jason A. Donenfeld" To: Jens Axboe Cc: tytso@mit.edu, hch@lst.de, linux-kernel@vger.kernel.org Subject: Re: [PATCH 1/2] random: convert to using fops->read_iter() Message-ID: References: <20220519193133.194138-1-axboe@kernel.dk> <20220519193133.194138-2-axboe@kernel.dk> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <20220519193133.194138-2-axboe@kernel.dk> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi Jens, On Thu, May 19, 2022 at 01:31:32PM -0600, Jens Axboe wrote: > for (;;) { > chacha20_block(chacha_state, output); > if (unlikely(chacha_state[12] == 0)) > ++chacha_state[13]; > > block_len = min_t(size_t, len, CHACHA_BLOCK_SIZE); > - left = copy_to_user(ubuf, output, block_len); > - if (left) { > - ret += block_len - left; > + block_len = copy_to_iter(output, block_len, to); > + if (!block_len) > break; > - } > > - ubuf += block_len; > ret += block_len; > len -= block_len; > - if (!len) > - break; > > BUILD_BUG_ON(PAGE_SIZE % CHACHA_BLOCK_SIZE != 0); > if (ret % PAGE_SIZE == 0) { > if (signal_pending(current)) > break; > cond_resched(); > } > } This isn't quite the same, is it? Before, it would immediately break out of the loop on any short copy. Now, it will only break out on a zero copy, which means it's possible that ret % PAGE_SIZE == 0, and there'll be an unnecessary cond_resched() before copy_to_iter() runs again and then breaks. Jason