linux-kernel - Re: block: DMA alignment of IO buffer allocated from slab

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Message-ID: <20180921072511.GA8188@ming.t460p>
Date:   Fri, 21 Sep 2018 15:25:13 +0800
From:   Ming Lei <ming.lei@...hat.com>
To:     Christoph Hellwig <hch@....de>
Cc:     Dave Chinner <david@...morbit.com>,
        Ming Lei <tom.leiming@...il.com>,
        linux-block <linux-block@...r.kernel.org>,
        linux-mm <linux-mm@...ck.org>,
        Linux FS Devel <linux-fsdevel@...r.kernel.org>,
        "open list:XFS FILESYSTEM" <linux-xfs@...r.kernel.org>,
        Dave Chinner <dchinner@...hat.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Jens Axboe <axboe@...nel.dk>
Subject: Re: block: DMA alignment of IO buffer allocated from slab

On Fri, Sep 21, 2018 at 09:08:05AM +0200, Christoph Hellwig wrote:
> On Fri, Sep 21, 2018 at 11:56:08AM +1000, Dave Chinner wrote:
> > > 3) If slab can't guarantee to return 512-aligned buffer, how to fix
> > > this data corruption issue?
> > 
> > I think that the block layer needs to check the alignment of memory
> > buffers passed to it and take appropriate action rather than
> > corrupting random memory and returning a sucess status to the bad
> > bio.
> 
> Or just reject the I/O.  But yes, we already have the
> queue_dma_alignment helper in the block layer, we just don't do it
> in the fast path.  I think generic_make_request_checks needs to
> check it, and print an error and return a warning if the alignment
> requirement isn't met.

That can be done in generic_make_request_checks(), but some cost may be
introduced, because each bvec needs to be checked in the fast path.

Thanks,
Ming