Re: [PATCH] block: fix get_max_io_size()

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On Fri, Aug 07, 2020 at 12:02:30PM -0700, Bart Van Assche wrote:
> On 2020-08-07 10:10, Keith Busch wrote:
> > On Fri, Aug 07, 2020 at 07:18:49AM -0700, Bart Van Assche wrote:
> >> Hi Keith,
> >>
> >> How about replacing your patch with the (untested) patch below?
> > 
> > 
> > I believe that should be fine, but I broke the kernel last time I did
> > something like that. I still think it was from incorrect queue_limits,
> > but Linus disagreed.
> > 
> >  * http://lkml.iu.edu/hypermail/linux/kernel/1601.2/03994.html
> 
> Hi Keith,
> 
> Thanks for the interesting link. Regarding Linus' comments about bio
> splitting: if the last return statement in get_max_io_size() is reached
> then it is guaranteed that sectors < pbs (physical block size). So I think
> that Linus' comment applies to the previous return statement instead of to
> the last ("return max_sectors - start_offset;"). However, I think it is
> already guaranteed that that value is a multiple of the logical block size
> because start_offset is a multiple of the logical block size and because
> of the following statement: "max_sectors &= ~(pbs - 1);".

This breaks if limits.max_sectors is not a multiple of the queue's
logical block size and the physical block size is larger than
max_sectors.



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