Re: block: DMA alignment of IO buffer allocated from slab

[Ming Lei]

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