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 X-Spam-Level: X-Spam-Status: No, score=-7.0 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_PASS autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 8A108C43381 for ; Fri, 1 Mar 2019 17:43:25 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 5FA5E20848 for ; Fri, 1 Mar 2019 17:43:25 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2388481AbfCARnX convert rfc822-to-8bit (ORCPT ); Fri, 1 Mar 2019 12:43:23 -0500 Received: from bhuna.collabora.co.uk ([46.235.227.227]:60676 "EHLO bhuna.collabora.co.uk" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727418AbfCARnX (ORCPT ); Fri, 1 Mar 2019 12:43:23 -0500 Received: from localhost (unknown [IPv6:2a01:e0a:2c:6930:5cf4:84a1:2763:fe0d]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) (Authenticated sender: bbrezillon) by bhuna.collabora.co.uk (Postfix) with ESMTPSA id 5CE33272BD9; Fri, 1 Mar 2019 17:43:20 +0000 (GMT) Date: Fri, 1 Mar 2019 18:43:17 +0100 From: Boris Brezillon To: "Tokunori Ikegami" Cc: "'Vignesh Raghavendra'" , "'liujian \(CE\)'" , , , , , , , , , Subject: Re: [PATCH v3] cfi: fix deadloop in cfi_cmdset_0002.c do_write_buffer Message-ID: <20190301184317.6bad546f@collabora.com> In-Reply-To: <000501d4d050$38eca160$aac5e420$@gmail.com> References: <1551189648-58073-1-git-send-email-liujian56@huawei.com> <016001d4cf71$865e7b60$931b7220$@gmail.com> <4F88C5DDA1E80143B232E89585ACE27D0264F137@DGGEMM528-MBX.china.huawei.com> <20190228164228.734ede80@collabora.com> <005a01d4d03e$39b0e0f0$ad12a2d0$@yahoo.co.jp> <4b3bc01a-3632-5dde-f683-94744ee7179d@ti.com> <000501d4d050$38eca160$aac5e420$@gmail.com> Organization: Collabora X-Mailer: Claws Mail 3.17.3 (GTK+ 2.24.32; x86_64-redhat-linux-gnu) MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8BIT Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Sat, 2 Mar 2019 01:59:41 +0900 "Tokunori Ikegami" wrote: > > [...] > > >>>>> In function do_write_buffer(), in the for loop, there is a > > >>>>> case chip_ready() returns 1 while chip_good() returns 0, so > > >>>>> it never break the loop. > > >>>>> To fix this, chip_good() is enough and it should timeout if > > >>>>> it stay bad for a while. > > >>>>> > > >>>>> Fixes: dfeae1073583("mtd: cfi_cmdset_0002: Change write > > >>>>> buffer to check correct value") > > >>>>> Signed-off-by: Yi Huaijie > > >>>>> Signed-off-by: Liu Jian > > >>>>> Reviewed-by: Tokunori Ikegami > > >>>>> --- > > >>>>> v2->v3: > > >>>>> Follow Vignesh's advice: > > >>>>> add one more check for check_good() even when time_after() > > >>>>> returns > > >> true. > > >>>>> > > >>>>> drivers/mtd/chips/cfi_cmdset_0002.c | 2 +- > > >>>>> 1 file changed, 1 insertion(+), 1 deletion(-) > > >>>>> > > >>>>> diff --git a/drivers/mtd/chips/cfi_cmdset_0002.c > > >>>>> b/drivers/mtd/chips/cfi_cmdset_0002.c > > >>>>> index 72428b6..3da2376 100644 > > >>>>> --- a/drivers/mtd/chips/cfi_cmdset_0002.c > > >>>>> +++ b/drivers/mtd/chips/cfi_cmdset_0002.c > > >>>>> @@ -1876,7 +1876,7 @@ static int __xipram > > >>>>> do_write_buffer(struct map_info *map, struct flchip *chip, > > >>>>> continue; > > >>>>> } > > >>>>> > > >>>>> - if (time_after(jiffies, timeo) > > >>>>> && !chip_ready(map, adr)) > > >>>>> + if (time_after(jiffies, timeo) > > >>>>> && !chip_good(map, adr, datum)) > > >>>> > > >>>> Just another idea to understand easily. > > >>>> > > >>>> unsigned long now = jiffies; > > >>>> > > >>>> if (chip_good(map, adr, datum)) { > > >>>> xip_enable(map, chip, adr); > > >>>> goto op_done; > > >>>> } > > >>>> > > >>>> if (time_after(now, timeo) { > > >>>> break; > > >>>> } > > >>>> > > >>> > > >>> Thank you~. It is more easier to understand！ > > >>> If there are no other comments, I will send new patch again ): > > >> > > >> Except this version no longer does what Vignesh suggested. See > > >> how you no longer test if chip_good() is true if time_after() > > >> returns true. So, imagine the thread entering this function is > > >> preempted just after the first chip_good() test, and resumed a > > >> few ms later. time_after() will return true, but chip_good() > > >> might also return true, and you ignore it. > > > > > > I think that the following 3 versions will be worked for > > > time_after() > > as a same result and follow the Vignesh-san suggestion. > > > > > > > As Boris explained above version 3 does not really follow my > > suggestion... Please see below > > > > > 1. Original Vignesh-san suggestion > > > > > > if (chip_good(map, adr, datum)) { > > > xip_enable(map, chip, adr); > > > goto op_done; > > > } > > > > > > if (time_after(jiffies, timeo)) { > > > /* Test chip_good() if TRUE incorrectly again so > > > write > > failure by time_after() can be avoided. */ > > > if (chip_good(map, adr, datum)) { > > > xip_enable(map, chip, adr); > > > goto op_done; > > > } > > > break; > > > } > > > > > > > > > Right, here we check chip_good() once _even when time_after() is > > true_ to avoid _spurious_ timeout > > > > > 2. Liujian-san v3 patch > > > > > > /* Test chip_good() if FALSE correctly so write failure > > > by > > time_after() can be avoided. */ > > > if (time_after(jiffies, timeo) && !chip_good(map, adr)) > > > break; > > > > > > if (chip_good(map, adr, datum)) { > > > xip_enable(map, chip, adr); > > > goto op_done; > > > } > > > > > > > This is a better version of 1 > > > > > 3. My idea > > > > > > /* Save current jiffies value before chip_good() to avoid > > > write > > failure by time_after() without testing chip_good() again. */ > > > unsigned long now = jiffies; > > > > > > if (chip_good(map, adr, datum)) { > > > xip_enable(map, chip, adr); > > > goto op_done; > > > } > > > > > > > What if thread gets pre-empted at this point and is re-scheduled > > exactly after timeo jiffies have elapsed? Below check would be true > > and exit loop > > I think that the jiffies value now is save before chip_good() so > below check would be false and not exit loop. True, I overlooked that part, and so Vignesh did. This proves one thing: code is not easier to follow with your version. IMO, if we want to make things clear, we should add a comment to Liujian's explaining why the extra test after time_after(jiffies, timeo) is needed.