Hi "Ahmed, Thank you for the patch! Perhaps something to improve: [auto build test WARNING on a9232dc5607dbada801f2fe83ea307cda762969a] url: https://github.com/0day-ci/linux/commits/Ahmed-S-Darwish/seqlock-Extend-s... base: a9232dc5607dbada801f2fe83ea307cda762969a config: s390-randconfig-s032-20200719 (attached as .config) compiler: s390-linux-gcc (GCC) 9.3.0 reproduce: wget https://raw.githubusercontent.com/intel/lkp-tests/master/sbin/make.cross -O ~/bin/make.cross chmod +x ~/bin/make.cross # apt-get install sparse # sparse version: v0.6.2-49-g707c5017-dirty # save the attached .config to linux build tree COMPILER_INSTALL_PATH=$HOME/0day COMPILER=gcc-9.3.0 make.cross C=1 CF='-fdiagnostic-prefix -D__CHECK_ENDIAN__' ARCH=s390 If you fix the issue, kindly add following tag as appropriate Reported-by: kernel test robot <lkp(a)intel.com&gt; sparse warnings: (new ones prefixed by >>) kernel/time/timekeeping.c:467:18: sparse: sparse: trying to copy expression type 31 include/linux/seqlock.h:340:16: sparse: sparse: unreplaced symbol 's' include/linux/seqlock.h:340:9: sparse: sparse: unreplaced symbol 'return' include/linux/seqlock.h:340:16: sparse: sparse: unreplaced symbol 's' include/linux/seqlock.h:340:9: sparse: sparse: unreplaced symbol 'return' kernel/time/timekeeping.c:467:18: sparse: sparse: unreplaced symbol 's' kernel/time/timekeeping.c:467:18: sparse: sparse: unreplaced symbol 'return' /bin/bash: line 1: 27836 Segmentation fault sparse -D__linux__ -Dlinux -D__STDC__ -Dunix -D__unix__ -Wbitwise -Wno-return-void -Wno-unknown-attribute -fdiagnostic-prefix -D__CHECK_ENDIAN__ -D__s390__ -D__s390x__ --arch=s390 -mbig-endian -m64 -Wp,-MMD,kernel/time/.timekeeping.o.d -nostdinc -isystem /opt/cross/gcc-9.3.0-nolibc/s390-linux/bin/../lib/gcc/s390-linux/9.3.0/include -Iarch/s390/include -I./arch/s390/include/generated -Iinclude -I./include -Iarch/s390/include/uapi -I./arch/s390/include/generated/uapi -Iinclude/uapi -I./include/generated/uapi -include include/linux/kconfig.h -include include/linux/compiler_types.h -D__KERNEL__ -DKBUILD_EXTRA_WARN1 -Wall -Wundef -Werror=strict-prototypes -Wno-trigraphs -fno-strict-aliasing -fno-common -fshort-wchar -fno-PIE -Werror=implicit-function-declaration -Werror=implicit-int -Wno-format-security -std=gnu89 -m64 -fPIE -mbackchain -msoft-float -march=z15 -mtune=z196 -Wa,-Iarch/s390/include -mindirect-branch=thunk -mfunction-return=thunk -mindirect-branch-table -DCC_USING_EXPOLINE -pipe -Wno-sign-compare -fno-asynchronous-unwind-tables -DCONFIG_AS_CFI_VAL_OFFSET=1 -fno-delete-null-pointer-checks -Wno-frame-address -Wno-format-truncation -Wno-format-overflow -Wno-address-of-packed-member -Os --param=allow-store-data-races=0 -fplugin=./scripts/gcc-plugins/randomize_layout_plugin.so -DRANDSTRUCT_PLUGIN -fno-reorder-blocks -fno-ipa-cp-clone -fno-partial-inlining -Wframe-larger-than=8192 -fno-stack-protector -Wno-unused-but-set-variable -Wimplicit-fallthrough -Wno-unused-const-variable -fomit-frame-pointer -fno-var-tracking-assignments -g -gdwarf-4 -femit-struct-debug-baseonly -fno-var-tracking -gz=zlib -fno-inline-functions-called-once -Wdeclaration-after-statement -Wvla -Wno-pointer-sign -Wno-stringop-truncation -Wno-array-bounds -Wno-stringop-overflow -Wno-restrict -Wno-maybe-uninitialized -fno-strict-overflow -fno-merge-all-constants -fmerge-constants -fno-stack-check -fconserve-stack -Werror=date-time -Werror=incompatible-pointer-types -Werror=designated-init -fmacro-prefix-map== -Wno-packed-not-aligned -Wextra -Wunused -Wno-unused-parameter -Wmissing-declarations -Wmissing-format-attribute -Wmissing-prototypes -Wold-style-definition -Wmissing-include-dirs -Wunused-but-set-variable -Wunused-const-variable -Wpacked-not-aligned -Wstringop-truncation -Wno-missing-field-initializers -Wno-sign-compare -fsanitize=kernel-address -fasan-shadow-offset=0x30000000000 --param asan-globals=1 --param asan-instrumentation-with-call-threshold=0 --param asan-stack=1 --param asan-instrument-allocas=1 -I kernel/time -I ./kernel/time -DKBUILD_MODFILE='"kernel/time/timekeeping"' -DKBUILD_BASENAME='"timekeeping"' -DKBUILD_MODNAME='"timekeeping"' kernel/time/timekeeping.c vim +458 kernel/time/timekeeping.c 4396e058c52e16 Thomas Gleixner 2014-07-16 418 4396e058c52e16 Thomas Gleixner 2014-07-16 419 /** 4396e058c52e16 Thomas Gleixner 2014-07-16 420 * ktime_get_mono_fast_ns - Fast NMI safe access to clock monotonic 4396e058c52e16 Thomas Gleixner 2014-07-16 421 * 4396e058c52e16 Thomas Gleixner 2014-07-16 422 * This timestamp is not guaranteed to be monotonic across an update. 4396e058c52e16 Thomas Gleixner 2014-07-16 423 * The timestamp is calculated by: 4396e058c52e16 Thomas Gleixner 2014-07-16 424 * 4396e058c52e16 Thomas Gleixner 2014-07-16 425 * now = base_mono + clock_delta * slope 4396e058c52e16 Thomas Gleixner 2014-07-16 426 * 4396e058c52e16 Thomas Gleixner 2014-07-16 427 * So if the update lowers the slope, readers who are forced to the 4396e058c52e16 Thomas Gleixner 2014-07-16 428 * not yet updated second array are still using the old steeper slope. 4396e058c52e16 Thomas Gleixner 2014-07-16 429 * 4396e058c52e16 Thomas Gleixner 2014-07-16 430 * tmono 4396e058c52e16 Thomas Gleixner 2014-07-16 431 * ^ 4396e058c52e16 Thomas Gleixner 2014-07-16 432 * | o n 4396e058c52e16 Thomas Gleixner 2014-07-16 433 * | o n 4396e058c52e16 Thomas Gleixner 2014-07-16 434 * | u 4396e058c52e16 Thomas Gleixner 2014-07-16 435 * | o 4396e058c52e16 Thomas Gleixner 2014-07-16 436 * |o 4396e058c52e16 Thomas Gleixner 2014-07-16 437 * |12345678---> reader order 4396e058c52e16 Thomas Gleixner 2014-07-16 438 * 4396e058c52e16 Thomas Gleixner 2014-07-16 439 * o = old slope 4396e058c52e16 Thomas Gleixner 2014-07-16 440 * u = update 4396e058c52e16 Thomas Gleixner 2014-07-16 441 * n = new slope 4396e058c52e16 Thomas Gleixner 2014-07-16 442 * 4396e058c52e16 Thomas Gleixner 2014-07-16 443 * So reader 6 will observe time going backwards versus reader 5. 4396e058c52e16 Thomas Gleixner 2014-07-16 444 * 4396e058c52e16 Thomas Gleixner 2014-07-16 445 * While other CPUs are likely to be able observe that, the only way 4396e058c52e16 Thomas Gleixner 2014-07-16 446 * for a CPU local observation is when an NMI hits in the middle of 4396e058c52e16 Thomas Gleixner 2014-07-16 447 * the update. Timestamps taken from that NMI context might be ahead 4396e058c52e16 Thomas Gleixner 2014-07-16 448 * of the following timestamps. Callers need to be aware of that and 4396e058c52e16 Thomas Gleixner 2014-07-16 449 * deal with it. 4396e058c52e16 Thomas Gleixner 2014-07-16 450 */ 4498e7467e9e44 Peter Zijlstra 2015-03-19 451 static __always_inline u64 __ktime_get_fast_ns(struct tk_fast *tkf) 4396e058c52e16 Thomas Gleixner 2014-07-16 452 { 4396e058c52e16 Thomas Gleixner 2014-07-16 453 struct tk_read_base *tkr; 4396e058c52e16 Thomas Gleixner 2014-07-16 454 unsigned int seq; 4396e058c52e16 Thomas Gleixner 2014-07-16 455 u64 now; 4396e058c52e16 Thomas Gleixner 2014-07-16 456 4396e058c52e16 Thomas Gleixner 2014-07-16 457 do { 7fc26327b75685 Peter Zijlstra 2015-05-27 @458 seq = raw_read_seqcount_latch(&tkf->seq); 4498e7467e9e44 Peter Zijlstra 2015-03-19 459 tkr = tkf->base + (seq & 0x01); 27727df240c7cc John Stultz 2016-08-23 460 now = ktime_to_ns(tkr->base); 27727df240c7cc John Stultz 2016-08-23 461 58bfea9532552d John Stultz 2016-10-04 462 now += timekeeping_delta_to_ns(tkr, 58bfea9532552d John Stultz 2016-10-04 463 clocksource_delta( ceea5e3771ed23 John Stultz 2017-06-08 464 tk_clock_read(tkr), 58bfea9532552d John Stultz 2016-10-04 465 tkr->cycle_last, 58bfea9532552d John Stultz 2016-10-04 466 tkr->mask)); 4498e7467e9e44 Peter Zijlstra 2015-03-19 467 } while (read_seqcount_retry(&tkf->seq, seq)); 4396e058c52e16 Thomas Gleixner 2014-07-16 468 4396e058c52e16 Thomas Gleixner 2014-07-16 469 return now; 4396e058c52e16 Thomas Gleixner 2014-07-16 470 } 4498e7467e9e44 Peter Zijlstra 2015-03-19 471 --- 0-DAY CI Kernel Test Service, Intel Corporation https://lists.01.org/hyperkitty/list/kbuild-all@lists.01.org