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

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Message-ID: <20180921070805.GC14529@lst.de>
Date:   Fri, 21 Sep 2018 09:08:05 +0200
From:   Christoph Hellwig <hch@....de>
To:     Dave Chinner <david@...morbit.com>
Cc:     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>,
        Christoph Hellwig <hch@....de>, Jens Axboe <axboe@...nel.dk>,
        Ming Lei <ming.lei@...hat.com>
Subject: Re: block: DMA alignment of IO buffer allocated from slab

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.