From: Tejun Heo <tj@xxxxxxxxxx> > Sent: 12 December 2024 17:19 > > On Thu, Dec 12, 2024 at 10:13:29AM -0700, Nathan Chancellor wrote: > > After a recent change to clamp() and its variants [1] that increases the > > coverage of the check that high is greater than low because it can be > > done through inlining, certain build configurations (such as s390 > > defconfig) fail to build with clang with: > > ... > > __propagate_weights() is called with an active value of zero in > > ioc_check_iocgs(), which results in the high value being less than the > > low value, which is undefined because the value returned depends on the > > order of the comparisons. > > > > The purpose of this expression is to ensure inuse is not more than > > active and at least 1. This could be written more simply with a ternary > > expression that uses min(inuse, active) as the condition so that the > > value of that condition can be used if it is not zero and one if it is. > > Do this conversion to resolve the error and add a comment to deter > > people from turning this back into clamp(). > > > > Link: https://lore.kernel.org/r/34d53778977747f19cce2abb287bb3e6@xxxxxxxxxxxxxxxx/ [1] > > Suggested-by: David Laight <david.laight@xxxxxxxxxx> > > Reported-by: Linux Kernel Functional Testing <lkft@xxxxxxxxxx> > > Closes: https://lore.kernel.org/llvm/CA+G9fYsD7mw13wredcZn0L-KBA3yeoVSTuxnss- > AEWMN3ha0cA@xxxxxxxxxxxxxx/ > > Reported-by: kernel test robot <lkp@xxxxxxxxx> > > Closes: https://lore.kernel.org/oe-kbuild-all/202412120322.3GfVe3vF-lkp@xxxxxxxxx/ > > Signed-off-by: Nathan Chancellor <nathan@xxxxxxxxxx> > > Acked-by: Tejun Heo <tj@xxxxxxxxxx> > > This likely deserves: > > Fixes: 7caa47151ab2 ("blkcg: implement blk-iocost") > Cc: stable@xxxxxxxxxxxxxxx # v5.4+ Especially since the old defn was: #define __clamp(val, lo, hi) \ ((val) >= (hi) ? (hi) : ((val) <= (lo) ? (lo) : (val))) so: - inuse = clamp_t(u32, inuse, 1, active); is zero if active is zero. David > > Thanks. > > -- > tejun - Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK Registration No: 1397386 (Wales)
