linux-kernel - Re: [PATCH 1/5] zram: handle multiple pages attached bio's bvec

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Message-ID: <20170403231315.GA8903@bbox>
Date:   Tue, 4 Apr 2017 08:13:15 +0900
From:   Minchan Kim <minchan.kim@....com>
To:     Andrew Morton <akpm@...ux-foundation.org>
CC:     Minchan Kim <minchan@...nel.org>, <linux-kernel@...r.kernel.org>,
        Sergey Senozhatsky <sergey.senozhatsky@...il.com>,
        <kernel-team@....com>, Jens Axboe <axboe@...nel.dk>,
        Hannes Reinecke <hare@...e.com>,
        Johannes Thumshirn <jthumshirn@...e.de>
Subject: Re: [PATCH 1/5] zram: handle multiple pages attached bio's bvec

Hi Andrew,

On Mon, Apr 03, 2017 at 03:45:28PM -0700, Andrew Morton wrote:
> On Mon, 3 Apr 2017 14:17:29 +0900 Minchan Kim <minchan@...nel.org> 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 panic.
> > 
> > It can be solved by limiting max_sectors with SECTORS_PER_PAGE like
> > [1] 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.
> > 
> > [1] 0bc315381fe9, zram: set physical queue limits to avoid array out of
> >     bounds accesses
> 
> This isn't a cleanup - it fixes a panic (or is it a BUG or is it an
> oops, or...)

I should have written more carefully.
Johannes reported the problem with fix[1] and Jens already sent it to the
mainline to fix it. However, during the discussion, we can solve the problem
nice way so this is revert of [1] plus solving the problem with other way
which no need to split bio.

Thanks.

> 
> How serious is this bug?  Should the fix be backported into -stable
> kernels?  etc.
> 
> A better description of the bug's behaviour would be appropriate.
> 
> > Cc: Jens Axboe <axboe@...nel.dk>
> > 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>
> > Signed-off-by: Johannes Thumshirn <jthumshirn@...e.de>
> > Signed-off-by: Minchan Kim <minchan@...nel.org>
> 
> This signoff trail is confusing.  It somewhat implies that Johannes
> authored the patch which I don't think is the case?
> 
>