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: <c795c090-430a-45a6-88b2-94033d50dea2@stanley.mountain>
Date: Wed, 4 Dec 2024 19:50:14 +0300
From: Dan Carpenter <dan.carpenter@...aro.org>
To: David Laight <David.Laight@...lab.com>, Tejun Heo <tj@...nel.org>
Cc: Naresh Kamboju <naresh.kamboju@...aro.org>,
	"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

Tejun probably reads everything to linux-block, but let's CC him explicitly.

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);

The other way to solve this would be to something stupid like:

diff --git a/block/blk-iocost.c b/block/blk-iocost.c
index 384aa15e8260..551edd2f661f 100644
--- a/block/blk-iocost.c
+++ b/block/blk-iocost.c
@@ -1094,7 +1094,7 @@ static void __propagate_weights(struct ioc_gq *iocg, u32 active, u32 inuse,
         * @active. An active internal node's inuse is solely determined by the
         * inuse to active ratio of its children regardless of @inuse.
         */
-       if (list_empty(&iocg->active_list) && iocg->child_active_sum) {
+       if ((list_empty(&iocg->active_list) && iocg->child_active_sum) || active == 0) {
                inuse = DIV64_U64_ROUND_UP(active * iocg->child_inuse_sum,
                                           iocg->child_active_sum);
        } else {

But that seems really stupid.

regards,
dan carpenter

On Wed, Dec 04, 2024 at 04:11:33PM +0000, David Laight wrote:
> 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
> 
> -
> Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK
> Registration No: 1397386 (Wales)