linux-kernel - Re: [PATCH v2 1/6] zram: handle multiple pages attached bio's bvec

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Date:   Thu, 13 Apr 2017 09:15:00 +0200
From:   Johannes Thumshirn <jthumshirn@...e.de>
To:     Minchan Kim <minchan@...nel.org>
Cc:     Andrew Morton <akpm@...ux-foundation.org>, kernel-team@....com,
        linux-kernel@...r.kernel.org, Hannes Reinecke <hare@...e.com>,
        Sergey Senozhatsky <sergey.senozhatsky@...il.com>
Subject: Re: [PATCH v2 1/6] zram: handle multiple pages attached bio's bvec

On Thu, Apr 13, 2017 at 11:59:20AM +0900, Minchan Kim wrote:
> Johannes Thumshirn reported system goes the panic when using NVMe over
> Fabrics loopback target with zram.
> 
> The reason is zram expects each bvec in bio contains a single page
> but nvme can attach a huge bulk of pages attached to the bio's bvec
> so that zram's index arithmetic could be wrong so that out-of-bound
> access makes system panic.
> 
> [1] in mainline solved solved the problem by limiting max_sectors with
> SECTORS_PER_PAGE but it makes zram slow because bio should split with
> each pages so this patch makes zram aware of multiple pages in a bvec
> so it could solve without any regression(ie, bio split).
> 
> [1] 0bc315381fe9, zram: set physical queue limits to avoid array out of
>     bounds accesses
> 
> * from v1
>   * Do not exceed page boundary when set up bv.bv_len in make_request
>   * change "remained" variable name with "unwritten"
> 
> Cc: Hannes Reinecke <hare@...e.com>
> Reported-by: Johannes Thumshirn <jthumshirn@...e.de>
> Tested-by: Johannes Thumshirn <jthumshirn@...e.de>
> Reviewed-by: Johannes Thumshirn <jthumshirn@...e.de>
> Reviewed-by: Sergey Senozhatsky <sergey.senozhatsky@...il.com>
> Signed-off-by: Minchan Kim <minchan@...nel.org>
> ---

Hi Minchan,

A quick amendment to your patch you forgot to remove the queue limit
setting which I introduced with commit 0bc315381fe9.

Thanks,
	Johannes

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