linux-kernel - 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

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Message-ID: <7920126775c74fa5915afbeedcfe2058@AcuMS.aculab.com>
Date: Wed, 4 Dec 2024 16:11:33 +0000
From: David Laight <David.Laight@...LAB.COM>
To: 'Dan Carpenter' <dan.carpenter@...aro.org>, Naresh Kamboju
	<naresh.kamboju@...aro.org>
CC: "linux-s390@...r.kernel.org" <linux-s390@...r.kernel.org>,
	clang-built-linux <llvm@...ts.linux.dev>, linux-block
	<linux-block@...r.kernel.org>, open list <linux-kernel@...r.kernel.org>,
	"lkft-triage@...ts.linaro.org" <lkft-triage@...ts.linaro.org>, "Linux
 Regressions" <regressions@...ts.linux.dev>, Anders Roxell
	<anders.roxell@...aro.org>, Arnd Bergmann <arnd@...db.de>, Nathan Chancellor
	<nathan@...nel.org>, Jens Axboe <axboe@...nel.dk>
Subject: 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

From: Dan Carpenter <dan.carpenter@...aro.org>
> Sent: 04 December 2024 14:39
> 
> Let's add David to the Cc list because he's the expert on clamp().

The traceback info misses the important point.
I can't see the 'inlined from line 2225' message.

We have (line 1084):
static void __propagate_weights(struct ioc_gq *iocg, u32 active, u32 inuse,
				bool save, struct ioc_now *now)
followed by:
		inuse = clamp_t(u32, inuse, 1, active);

But line 2225 has:
	__propagate_weights(iocg, 0, 0, false, now);

With aggressive inlining the compiler sees 'active == 0'
and the lo > hi test correctly triggers.

The previous version only verified 'lo <= hi' if it was a constant
integer expression - which it isn't here.

No idea what the code is trying to do, nor what value it expects
clamp(val, 1, 0) to generate - likely to be 0 or 1 depending on
the order of the comparisons.

	David

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