linux-kernel - Re: [PATCH] nvmet: convert from kmap to nvmet_copy_from

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Message-ID: <6dfa2fbf-78e6-2c7b-f6e3-c765fe5015c2@mellanox.com>
Date:   Wed, 19 Apr 2017 12:44:50 +0300
From:   Max Gurtovoy <maxg@...lanox.com>
To:     Johannes Thumshirn <jthumshirn@...e.de>
CC:     Logan Gunthorpe <logang@...tatee.com>,
        <linux-nvme@...ts.infradead.org>, <linux-kernel@...r.kernel.org>,
        Christoph Hellwig <hch@....de>,
        Sagi Grimberg <sagi@...mberg.me>
Subject: Re: [PATCH] nvmet: convert from kmap to nvmet_copy_from_sgl



On 4/19/2017 12:38 PM, Johannes Thumshirn wrote:
> On Wed, Apr 19, 2017 at 12:33:09PM +0300, Max Gurtovoy wrote:
>> Hi Logan,
>>
>> On 4/19/2017 2:32 AM, Logan Gunthorpe wrote:
>>> This is safer as it doesn't rely on the data being stored in
>>> a single page in an sgl.
>>>
>>> It also aids our effort to start phasing out users of sg_page. See [1].
>>>
>>> For this we kmalloc some memory, copy to it and free at the end. Note:
>>> we can't allocate this memory on the stack as the kbuild test robot
>>> reports some frame size overflows on i386.
>>>
>>> [1] https://lwn.net/Articles/720053/
>>>
>>> Signed-off-by: Logan Gunthorpe <logang@...tatee.com>
>>> Cc: Christoph Hellwig <hch@....de>
>>> Cc: Sagi Grimberg <sagi@...mberg.me>
>>> ---
>>> drivers/nvme/target/fabrics-cmd.c | 32 +++++++++++++++++++++++++-------
>>> 1 file changed, 25 insertions(+), 7 deletions(-)
>>>
>>> diff --git a/drivers/nvme/target/fabrics-cmd.c b/drivers/nvme/target/fabrics-cmd.c
>>> index 8bd022af..2e0ab10 100644
>>> --- a/drivers/nvme/target/fabrics-cmd.c
>>> +++ b/drivers/nvme/target/fabrics-cmd.c
>>> @@ -122,7 +122,15 @@ static void nvmet_execute_admin_connect(struct nvmet_req *req)
>>> 	struct nvmet_ctrl *ctrl = NULL;
>>> 	u16 status = 0;
>>>
>>> -	d = kmap(sg_page(req->sg)) + req->sg->offset;
>>> +	d = kmalloc(sizeof(*d), GFP_KERNEL);
>>
>> I'd prefer removing the dynamic allocation and use d on the stack to
>> simplify the code.
>> Any thoughts ?
>
> Hi Max,
>
> Pasting from above:
>
>>> we can't allocate this memory on the stack as the kbuild test robot
>>> reports some frame size overflows on i386.

Thanks Johannes, I missed that comment.

Looks good,

Reviewed-by: Max Gurtovoy <maxg@...lanox.com>

>
>