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: > > 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 > 1101 | inuse = clamp_t(u32, inuse, 1, active); > | ^ > include/linux/minmax.h:218:36: note: expanded from macro 'clamp_t' > 218 | #define clamp_t(type, val, lo, hi) __careful_clamp(type, val, lo, hi) > | ^ > include/linux/minmax.h:195:2: note: expanded from macro '__careful_clamp' > 195 | __clamp_once(type, val, lo, hi, __UNIQUE_ID(v_), __UNIQUE_ID(l_), __UNIQUE_ID(h_)) > | ^ > include/linux/minmax.h:188:2: note: expanded from macro '__clamp_once' > 188 | BUILD_BUG_ON_MSG(statically_true(ulo > uhi), \ > | ^ > > __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+ Thanks. -- tejun
