5.4-stable review patch. If anyone has any objections, please let me know.
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From: Nathan Chancellor nathan@kernel.org
[ Upstream commit 57e420c84f9ab55ba4c5e2ae9c5f6c8e1ea834d2 ]
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().
Fixes: 7caa47151ab2 ("blkcg: implement blk-iocost") Link: https://lore.kernel.org/r/34d53778977747f19cce2abb287bb3e6@AcuMS.aculab.com/ [1] Suggested-by: David Laight david.laight@aculab.com Reported-by: Linux Kernel Functional Testing lkft@linaro.org Closes: https://lore.kernel.org/llvm/CA+G9fYsD7mw13wredcZn0L-KBA3yeoVSTuxnss-AEWMN3h... Reported-by: kernel test robot lkp@intel.com Closes: https://lore.kernel.org/oe-kbuild-all/202412120322.3GfVe3vF-lkp@intel.com/ Signed-off-by: Nathan Chancellor nathan@kernel.org Acked-by: Tejun Heo tj@kernel.org Signed-off-by: Jens Axboe axboe@kernel.dk Signed-off-by: Sasha Levin sashal@kernel.org --- block/blk-iocost.c | 9 ++++++++- 1 file changed, 8 insertions(+), 1 deletion(-)
diff --git a/block/blk-iocost.c b/block/blk-iocost.c index 1acd96c9d5c0..642b16e59dd0 100644 --- a/block/blk-iocost.c +++ b/block/blk-iocost.c @@ -916,7 +916,14 @@ static void __propagate_active_weight(struct ioc_gq *iocg, u32 active, u32 inuse inuse = DIV64_U64_ROUND_UP(active * iocg->child_inuse_sum, iocg->child_active_sum); } else { - inuse = clamp_t(u32, inuse, 1, active); + /* + * It may be tempting to turn this into a clamp expression with + * a lower limit of 1 but active may be 0, which cannot be used + * as an upper limit in that situation. This expression allows + * active to clamp inuse unless it is 0, in which case inuse + * becomes 1. + */ + inuse = min(inuse, active) ?: 1; }
if (active == iocg->active && inuse == iocg->inuse)