Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755249Ab0A0OUA (ORCPT ); Wed, 27 Jan 2010 09:20:00 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1755230Ab0A0OT7 (ORCPT ); Wed, 27 Jan 2010 09:19:59 -0500 Received: from mail-pz0-f189.google.com ([209.85.222.189]:52459 "EHLO mail-pz0-f189.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754017Ab0A0OT6 (ORCPT ); Wed, 27 Jan 2010 09:19:58 -0500 DomainKey-Signature: a=rsa-sha1; c=nofws; d=gmail.com; s=gamma; h=message-id:date:from:user-agent:mime-version:to:cc:subject :references:in-reply-to:content-type:content-transfer-encoding; b=LRG5OU/w+ljy45gJ2TkOtSroHYqSfKWfsZkxF36kUo0/k7AK85wGcVyus+RbLIM+yz ZxpBsL8DJ5odphr4FvPVmyMliYUZtygRjf6tZ3T3/Oy1PowDcHwMdVirVlXd6BpGEvpq PnIHjL+ElbH88QadQezYh6TZBFch8iflOYYiQ= Message-ID: <4B604B86.9040307@gmail.com> Date: Wed, 27 Jan 2010 22:19:50 +0800 From: Liuwenyi User-Agent: Mozilla/5.0 (X11; U; Linux i686; en-US; rv:1.9.1.7) Gecko/20100120 Fedora/3.0.1-1.fc12 Thunderbird/3.0.1 MIME-Version: 1.0 To: "Yan, Zheng " CC: chris.mason@oracle.com, jbacik@redhat.com, jens.axboe@oracle.com, linux-btrfs , linux-kernel@vger.kernel.org, strongzgy@gmail.com Subject: Re: [PATCH]btrfs: avoid comparing with NULL pointer References: <4B5FDCD1.8060806@gmail.com> <3d0408631001270000w49fc9100yb1e3b59df2e032e9@mail.gmail.com> In-Reply-To: <3d0408631001270000w49fc9100yb1e3b59df2e032e9@mail.gmail.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1879 Lines: 62 于 2010年01月27日 16:00, Yan, Zheng 写道: > 2010/1/27 Liuwenyi: > >> In this patch, I adjust the seqence of if-conditions. >> It will assess the page->private situation. >> First, we make sure the page->private is not null. >> And then, we can do some with this page->private. >> >> --- >> Signed-off-by: Liuwenyi >> Cc: Chris Mason >> Cc: Yan Zheng >> Cc: Josef Bacik >> Cc: Jens Axboe >> Cc: linux-btrfs@vger.kernel.org >> Cc: linux-kernel@vger.kernel.org >> >> --- >> fs/btrfs/disk-io.c | 4 ++-- >> 1 files changed, 2 insertions(+), 2 deletions(-) >> >> diff --git a/fs/btrfs/disk-io.c b/fs/btrfs/disk-io.c >> index 009e3bd..a300dca 100644 >> --- a/fs/btrfs/disk-io.c >> +++ b/fs/btrfs/disk-io.c >> @@ -1407,11 +1407,11 @@ static int bio_ready_for_csum(struct bio *bio) >> >> bio_for_each_segment(bvec, bio, i) { >> page = bvec->bv_page; >> - if (page->private == EXTENT_PAGE_PRIVATE) { >> + if (!page->private) { >> length += bvec->bv_len; >> continue; >> } >> - if (!page->private) { >> + if (page->private == EXTENT_PAGE_PRIVATE) { >> length += bvec->bv_len; >> continue; >> } >> -- >> > Why do you want to do this? The code is perfect safe even > page->private is NULL. Furthermore, your patch is malformed. > > Yan, Zheng > Yes, I agree with you, this code is safe. But I think we should check whether the pointer is available first. It is unnecessary judge the "(page->private == EXTENT_PAGE_PRIVATE)" while page->private is null. --- Best Regards, Liuwenyi 2010-1-27 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/