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[209.85.220.65]) by mx.google.com with SMTPS id j127sor3370422ybj.150.2019.03.04.10.57.01 for (Google Transport Security); Mon, 04 Mar 2019 10:57:01 -0800 (PST) Received-SPF: pass (google.com: domain of dennisszhou@gmail.com designates 209.85.220.65 as permitted sender) client-ip=209.85.220.65; Authentication-Results: mx.google.com; spf=pass (google.com: domain of dennisszhou@gmail.com designates 209.85.220.65 as permitted sender) smtp.mailfrom=dennisszhou@gmail.com; dmarc=fail (p=NONE sp=NONE dis=NONE) header.from=kernel.org X-Google-Smtp-Source: APXvYqztRwnWv3pEawsYV9qGAllROIkrxq4e/0Xg9sZbcOXkL9oitOsG1/kCKgLP8oeAMJulyQT5bg== X-Received: by 2002:a25:949:: with SMTP id u9mr15934919ybm.98.1551725821353; Mon, 04 Mar 2019 10:57:01 -0800 (PST) Received: from dennisz-mbp.dhcp.thefacebook.com ([2620:10d:c091:200::1:8d76]) by smtp.gmail.com with ESMTPSA id d85sm3189818ywd.96.2019.03.04.10.56.59 (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Mon, 04 Mar 2019 10:57:00 -0800 (PST) Date: Mon, 4 Mar 2019 13:56:57 -0500 From: "dennis@kernel.org" To: Peng Fan Cc: "tj@kernel.org" , "cl@linux.com" , "linux-mm@kvack.org" , "linux-kernel@vger.kernel.org" , "van.freenix@gmail.com" Subject: Re: [PATCH 2/2] percpu: pcpu_next_md_free_region: inclusive check for PCPU_BITMAP_BLOCK_BITS Message-ID: <20190304185657.GA17970@dennisz-mbp.dhcp.thefacebook.com> References: <20190304104541.25745-1-peng.fan@nxp.com> <20190304104541.25745-2-peng.fan@nxp.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190304104541.25745-2-peng.fan@nxp.com> User-Agent: Mutt/1.10.1 (2018-07-13) X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: Hi Peng, On Mon, Mar 04, 2019 at 10:33:55AM +0000, Peng Fan wrote: > If the block [contig_hint_start, contig_hint_start + contig_hint) > matches block->right_free area, need use "<=", not "<". > > Signed-off-by: Peng Fan > --- > > V1: > Based on https://patchwork.kernel.org/cover/10832459/ applied linux-next > boot test on qemu aarch64 > > mm/percpu.c | 3 ++- > 1 file changed, 2 insertions(+), 1 deletion(-) > > diff --git a/mm/percpu.c b/mm/percpu.c > index 5ee90fc34ea3..0f91f1d883c6 100644 > --- a/mm/percpu.c > +++ b/mm/percpu.c > @@ -390,7 +390,8 @@ static void pcpu_next_md_free_region(struct pcpu_chunk *chunk, int *bit_off, > */ > *bits = block->contig_hint; > if (*bits && block->contig_hint_start >= block_off && > - *bits + block->contig_hint_start < PCPU_BITMAP_BLOCK_BITS) { > + *bits + block->contig_hint_start <= > + PCPU_BITMAP_BLOCK_BITS) { > *bit_off = pcpu_block_off_to_off(i, > block->contig_hint_start); > return; > -- > 2.16.4 > This is wrong. This iterator is for updating contig hints and not for finding fit. Have you tried reproducing and proving the issue you are seeing? In general, making changes to percpu carries a lot of risk. I really only want to be taking code that is provably solving a problem and not supported by just code inspection. Boot testing for a change like this is really not enough as we need to be sure changes like these are correct. Thanks, Dennis