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

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Message-ID: <20170419093826.GB10632@linux-x5ow.site>
Date:   Wed, 19 Apr 2017 11:38:26 +0200
From:   Johannes Thumshirn <jthumshirn@...e.de>
To:     Max Gurtovoy <maxg@...lanox.com>
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 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.


-- 
Johannes Thumshirn                                          Storage
jthumshirn@...e.de                                +49 911 74053 689
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