linux-kernel - Re: [PATCH v7 16/21] block: add check when merging zone device pages

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <20220704060700.GA28966@lst.de>
Date:   Mon, 4 Jul 2022 08:07:00 +0200
From:   Christoph Hellwig <hch@....de>
To:     Logan Gunthorpe <logang@...tatee.com>
Cc:     Christoph Hellwig <hch@....de>, linux-kernel@...r.kernel.org,
        linux-nvme@...ts.infradead.org, linux-block@...r.kernel.org,
        linux-pci@...r.kernel.org, linux-mm@...ck.org,
        iommu@...ts.linux-foundation.org,
        Stephen Bates <sbates@...thlin.com>,
        Dan Williams <dan.j.williams@...el.com>,
        Jason Gunthorpe <jgg@...pe.ca>,
        Christian König <christian.koenig@....com>,
        John Hubbard <jhubbard@...dia.com>,
        Don Dutile <ddutile@...hat.com>,
        Matthew Wilcox <willy@...radead.org>,
        Daniel Vetter <daniel.vetter@...ll.ch>,
        Minturn Dave B <dave.b.minturn@...el.com>,
        Jason Ekstrand <jason@...kstrand.net>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Xiong Jianxin <jianxin.xiong@...el.com>,
        Bjorn Helgaas <helgaas@...nel.org>,
        Ira Weiny <ira.weiny@...el.com>,
        Robin Murphy <robin.murphy@....com>,
        Martin Oliveira <martin.oliveira@...eticom.com>,
        Chaitanya Kulkarni <ckulkarnilinux@...il.com>,
        Ralph Campbell <rcampbell@...dia.com>
Subject: Re: [PATCH v7 16/21] block: add check when merging zone device
 pages

On Thu, Jun 30, 2022 at 03:50:10PM -0600, Logan Gunthorpe wrote:
> Oh, it turns out this code has nothing to do with REQ_NOMERGE. It's used
> indirectly in bio_map_user_iov() and __bio_iov_iter_get_pages() when
> adding pages to the bio via page_is_mergeable(). So it's not about
> requests being merged it's about pages being merged.

Oh, true.

> So I'm not sure how we can avoid this, but it only happens when two
> adjacent pages are added to the same bio in a row, so I don't think it's
> that common, but the check can probably be moved down so it happens
> after the same_page check to make it a little less common.

Yes, looks like we have to keep it.