From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751786AbeAZRbp (ORCPT ); Fri, 26 Jan 2018 12:31:45 -0500 Received: from zeniv.linux.org.uk ([195.92.253.2]:46108 "EHLO ZenIV.linux.org.uk" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751438AbeAZRbc (ORCPT ); Fri, 26 Jan 2018 12:31:32 -0500 Date: Fri, 26 Jan 2018 17:31:30 +0000 From: Al Viro To: Jia-Ju Bai Cc: tim@cyberelk.net, linux-kernel@vger.kernel.org Subject: Re: [PATCH] block: paride: on26: Replace mdelay with msleep in on26_test_port Message-ID: <20180126173130.GZ13338@ZenIV.linux.org.uk> References: <1516981345-8202-1-git-send-email-baijiaju1990@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1516981345-8202-1-git-send-email-baijiaju1990@gmail.com> User-Agent: Mutt/1.9.1 (2017-09-22) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, Jan 26, 2018 at 11:42:25PM +0800, Jia-Ju Bai wrote: > After checking all possible call chains to on26_test_port() here, > my tool finds that this function is never called in atomic context, > namely never in an interrupt handler or holding a spinlock. > And on26_test_port() is only called by pi_probe_unit() that calls > wait_event() through pi_claim(), > so it indicates that on26_test_port() can call functions that can sleep. > Thus mdelay can be replaced with msleep to avoid busy wait. Sigh... Here's how I would've written it: " on26_test_port() is never called from atomic contexts. It has no direct callers and it is reachable only via ->test_port. ->test_port has only one user: drivers/block/paride/paride.c:322: max = pi->proto->test_port(pi); in pi_probe_unit(). That gets called only from pi_init(), called from p{d,cd,f,t,g}_detect(), called from module_init stuff, all of the above without entering atomic contexts along the way. Despite never getting called from atomic contexts, on26_test_port() contains mdelay(100), i.e. busy-loops for 0.1s; that's neither nice nor needed, since msleep() would serve just as well. Found by [reference to tool]"