linux-kernel - Re: [PATCH V1] lib/scatterlist: Fix to calculate the last

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Message-ID: <Y8V27yFgM60+KS1a@nvidia.com>
Date:   Mon, 16 Jan 2023 12:10:23 -0400
From:   Jason Gunthorpe <jgg@...dia.com>
To:     Yishai Hadas <yishaih@...dia.com>
Cc:     linux-kernel@...r.kernel.org, linux-block@...r.kernel.org,
        linux-mm@...ck.org, axboe@...nel.dk, logang@...tatee.com,
        akpm@...ux-foundation.org, willy@...radead.org, hch@....de,
        alex.williamson@...hat.com, leonro@...dia.com, maorg@...dia.com
Subject: Re: [PATCH V1] lib/scatterlist: Fix to calculate the last_pg properly

On Wed, Jan 11, 2023 at 12:10:54PM +0200, Yishai Hadas wrote:
> The last_pg is wrong, it is actually the first page of the last
> scatterlist element. To get the last page of the last scatterlist
> element we have to add prv->length. So it is checking mergability
> against the wrong page, Further, a SG element is not guaranteed to end
> on a page boundary, so we have to check the sub page location also for
> merge eligibility.
> 
> Fix the above by checking physical contiguity based on PFNs, compute the
> actual last page and then call pages_are_mergable().
> 
> Fixes: 1567b49d1a40 ("lib/scatterlist: add check when merging zone device pages")
> Reported-by: Jason Gunthorpe <jgg@...dia.com>
> Signed-off-by: Yishai Hadas <yishaih@...dia.com>

Applied to rdma for-rc

Thanks,
Jason