RE: s390: block/blk-iocost.c:1101:11: error: call to '__compiletime_assert_557' declared with 'error' attribute: clamp() low limit 1 greater than high limit active

[David Laight <David.Laight@ACULAB.COM>]

From: Tejun Heo
> Sent: 04 December 2024 17:41
> 
> Hello,
> 
> On Wed, Dec 04, 2024 at 07:50:14PM +0300, Dan Carpenter wrote:
> > Tejun probably reads everything to linux-block, but let's CC him explicitly.
> 
> Oh, I'm not. Thanks for cc'ing.
> 
> > block/blk-iocost.c
> >   2222                          TRACE_IOCG_PATH(iocg_idle, iocg, now,
> >   2223                                          atomic64_read(&iocg->active_period),
> >   2224                                          atomic64_read(&ioc->cur_period), vtime);
> >   2225                          __propagate_weights(iocg, 0, 0, false, now);
> >                                                           ^
> > Why is "active" zero?  __propagate_weights() does a clamp() to 1 as minimum and
> > we've added new build time asserts so this breaks the build.
> >
> >   2226                          list_del_init(&iocg->active_list);
> >
...
> 
> This is a good catch. It's impressive that this can be caught at compile
> time. The upper limit can become zero but the lower limit should win as
> that's there to protect against divide by zero, so I think the right thinig
> to do is replacing clamp() with max(min()). Is someone interested in writing
> up the patch and sending it Jens' way?

Perhaps if written as:
	inuse = min(inuse, active) ?: 1;
it might stop someone changing it back.

	David

	

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