linux-kernel - Re: [PATCH 08/16] dm-writecache: use bvec_kmap_local instead of bvec_kmap

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Message-ID: <20210608163802.GA12173@lst.de>
Date:   Tue, 8 Jun 2021 18:38:02 +0200
From:   Christoph Hellwig <hch@....de>
To:     Bart Van Assche <bvanassche@....org>
Cc:     Christoph Hellwig <hch@....de>, Jens Axboe <axboe@...nel.dk>,
        Thomas Bogendoerfer <tsbogend@...ha.franken.de>,
        Geoff Levand <geoff@...radead.org>,
        Ilya Dryomov <idryomov@...il.com>,
        Dongsheng Yang <dongsheng.yang@...ystack.cn>,
        Mike Snitzer <snitzer@...hat.com>,
        Ira Weiny <ira.weiny@...el.com>, dm-devel@...hat.com,
        linux-mips@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-block@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org,
        ceph-devel@...r.kernel.org
Subject: Re: [PATCH 08/16] dm-writecache: use bvec_kmap_local instead of
 bvec_kmap_irq

On Tue, Jun 08, 2021 at 09:30:56AM -0700, Bart Van Assche wrote:
> >From one of the functions called by kunmap_local():
> 
> unsigned long addr = (unsigned long) vaddr & PAGE_MASK;
> 
> This won't work well if bvec->bv_offset >= PAGE_SIZE I assume?

It won't indeed.  Both the existing and new helpers operate on single
page bvecs only, and all callers only use those.  I should have
probably mentioned that in the cover letter and documented the
assumptions in the code, though.