Re: block: don't check request size in blk_cloned_rq_check_limits()

[Christoph Hellwig <hch@infradead.org>]

On Sat, Jun 11, 2016 at 03:10:06PM +0200, Hannes Reinecke wrote:
> Well, the primary issue is that 'blk_cloned_rq_check_limits()' doesn't check
> for BLOCK_PC, so this particular check would be applied for every request.

So fix it..

> But as it turns out, even adding a check for BLOCK_PC doesn't help, so we're
> indeed seeing REQ_TYPE_FS requests with larger max_sector counts.
> 
> As to _why_ this happens I frankly have no idea. I have been staring at this
> particular code for over a year now (I've got another bug pending where we
> hit the _other_ if clause), but to no avail.
> So I've resolved to drop the check altogether, seeing that max_sector size
> is _not_ something which gets changed during failover.
> Therefore if the max_sector count is wrong for the cloned request it was
> already wrong for the original request, and we should've errored it out far
> earlier.
> The max_segments count, OTOH, _might_ change during failover (different
> hardware has different max_segments setting, and this is being changed
> during sg mapping), so there is some value to be had from testing it here.

I really think we need to drill down and figure out what's going on here
first.