Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) client-ip=23.128.96.18;
Received-SPF: Pass (protection.outlook.com: domain of nvidia.com designates
 216.228.112.35 as permitted sender) receiver=protection.outlook.com;
 client-ip=216.228.112.35; helo=mail.nvidia.com;
Subject: Re: [PATCH rdma-next v4 2/3] lib/scatterlist: Fix wrong update of
 orig_nents
To:     Jason Gunthorpe <jgg@nvidia.com>
CC:     <dledford@redhat.com>, <hch@infradead.org>, <leonro@nvidia.com>,
        <aelior@marvell.com>, <daniel@ffwll.ch>, <airlied@linux.ie>,
        <dennis.dalessandro@cornelisnetworks.com>,
        <dri-devel@lists.freedesktop.org>,
        <intel-gfx@lists.freedesktop.org>, <jani.nikula@linux.intel.com>,
        <joonas.lahtinen@linux.intel.com>, <linux-kernel@vger.kernel.org>,
        <linux-rdma@vger.kernel.org>, <maarten.lankhorst@linux.intel.com>,
        <mripard@kernel.org>, <mkalderon@marvell.com>,
        <mike.marciniszyn@cornelisnetworks.com>,
        <mustafa.ismail@intel.com>, <rodrigo.vivi@intel.com>,
        <sroland@vmware.com>, <shiraz.saleem@intel.com>,
        <tzimmermann@suse.de>, <linux-graphics-maintainer@vmware.com>,
        <liweihang@huawei.com>, <liangwenpeng@huawei.com>,
        <yishaih@nvidia.com>, <zackr@vmware.com>, <zyjzyj2000@gmail.com>
References: <20210824142531.3877007-1-maorg@nvidia.com>
 <20210824142531.3877007-3-maorg@nvidia.com>
 <20210824191248.GY1721383@nvidia.com>
From:   Maor Gottlieb <maorg@nvidia.com>
Message-ID: <4f4a712a-71d4-ebac-48f2-766bfda61f1e@nvidia.com>
Date:   Wed, 25 Aug 2021 07:59:27 +0300
User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:78.0) Gecko/20100101
 Thunderbird/78.13.0
MIME-Version: 1.0
In-Reply-To: <20210824191248.GY1721383@nvidia.com>
Content-Type: text/plain; charset="utf-8"; format=flowed
Content-Transfer-Encoding: 7bit
Content-Language: en-US
X-MS-Exchange-CrossTenant-OriginalArrivalTime: 25 Aug 2021 04:59:39.8920
 (UTC)
X-MS-Exchange-CrossTenant-Network-Message-Id: f39f0131-c144-4fd0-b0b4-08d96785251d
X-MS-Exchange-CrossTenant-Id: 43083d15-7273-40c1-b7db-39efd9ccc17a
X-MS-Exchange-CrossTenant-OriginalAttributedTenantConnectingIp: TenantId=43083d15-7273-40c1-b7db-39efd9ccc17a;Ip=[216.228.112.35];Helo=[mail.nvidia.com]
X-MS-Exchange-CrossTenant-AuthSource: BN8NAM11FT020.eop-nam11.prod.protection.outlook.com
X-MS-Exchange-CrossTenant-AuthAs: Anonymous
X-MS-Exchange-CrossTenant-FromEntityHeader: HybridOnPrem
X-MS-Exchange-Transport-CrossTenantHeadersStamped: MN2PR12MB4238
Precedence: bulk
List-ID: <linux-kernel.vger.kernel.org>
X-Mailing-List: linux-kernel@vger.kernel.org


On 8/24/2021 10:12 PM, Jason Gunthorpe wrote:
> On Tue, Aug 24, 2021 at 05:25:30PM +0300, Maor Gottlieb wrote:
>> @@ -514,11 +531,13 @@ struct scatterlist *sg_alloc_append_table_from_pages(struct sg_table *sgt,
>>   		offset = 0;
>>   		cur_page = j;
>>   	}
>> -	sgt->nents += added_nents;
>> +	sgt_append->sgt.nents += added_nents;
>> +	sgt_append->sgt.orig_nents = sgt_append->sgt.nents;
>> +	sgt_append->prv = s;
> Why is nents being touched here?
>
> Shouldn't it just be
>
>      sgt_append->sgt.orig_nents += added_nents;
>      sgt_append->prv = s;
>
> ?

In general yes, but all the sg_alloc_* functions update both orig_nents 
and nents (to same value). May be drivers that pass nents instead of 
orig_nents to dma_map_sg* (like umem did before this patch set). So I 
prefer to set it here as well, also not to break 
sg_alloc_table_from_pages_segment which use the same path. This kind of 
change could be done very carefully next cycle for all sg_alloc_*.

>
> Let me know I can fix it
>
> Jason