Hi Waiman, [FYI, it's a private test report for your RFC patch.] [auto build test ERROR on tip/locking/core] [also build test ERROR on tip/master arm-perf/for-next/perf v5.10-rc4 next-20201118] [If your patch is applied to the wrong git tree, kindly drop us a note. And when submitting patch, we suggest to use '--base' as documented in https://git-scm.com/docs/git-format-patch] url: https://github.com/0day-ci/linux/commits/Waiman-Long/locking-rwsem-Rework... base: https://git.kernel.org/pub/scm/linux/kernel/git/tip/tip.git 932f8c64d38bb08f69c8c26a2216ba0c36c6daa8 config: nios2-randconfig-r022-20201118 (attached as .config) compiler: nios2-linux-gcc (GCC) 9.3.0 reproduce (this is a W=1 build): wget https://raw.githubusercontent.com/intel/lkp-tests/master/sbin/make.cross -O ~/bin/make.cross chmod +x ~/bin/make.cross # https://github.com/0day-ci/linux/commit/8ba2157a62de4ca5c3a922faaea7c2b2a... git remote add linux-review https://github.com/0day-ci/linux git fetch --no-tags linux-review Waiman-Long/locking-rwsem-Rework-reader-optimistic-spinning/20201118-110810 git checkout 8ba2157a62de4ca5c3a922faaea7c2b2ab2ca8a7 # save the attached .config to linux build tree COMPILER_INSTALL_PATH=$HOME/0day COMPILER=gcc-9.3.0 make.cross ARCH=nios2 If you fix the issue, kindly add following tag as appropriate Reported-by: kernel test robot <lkp(a)intel.com&gt; All errors (new ones prefixed by >>): kernel/locking/rwsem.c: In function 'rwsem_down_write_slowpath': 1016 | if (rwsem_can_spin_on_owner(sem) && rwsem_optimistic_spin(sem)) { | ^~~~~~~~~~~~~~~~~~~~~~~ kernel/locking/rwsem.c:855:20: note: declared here 855 | static inline bool rwsem_can_spin_on_owner(struct rw_semaphore *sem, | ^~~~~~~~~~~~~~~~~~~~~~~ 1016 | if (rwsem_can_spin_on_owner(sem) && rwsem_optimistic_spin(sem)) { | ^~~~~~~~~~~~~~~~~~~~~ kernel/locking/rwsem.c:861:20: note: declared here 861 | static inline bool rwsem_optimistic_spin(struct rw_semaphore *sem, bool wlock) | ^~~~~~~~~~~~~~~~~~~~~ vim +/rwsem_can_spin_on_owner +1016 kernel/locking/rwsem.c 1002 1003 /* 1004 * Wait until we successfully acquire the write lock 1005 */ 1006 static struct rw_semaphore * 1007 rwsem_down_write_slowpath(struct rw_semaphore *sem, int state) 1008 { 1009 long count; 1010 enum writer_wait_state wstate; 1011 struct rwsem_waiter waiter; 1012 struct rw_semaphore *ret = sem; 1013 DEFINE_WAKE_Q(wake_q); 1014 1015 /* do optimistic spinning and steal lock if possible */ 1017 /* rwsem_optimistic_spin() implies ACQUIRE on success */ 1018 return sem; 1019 } 1020 1021 /* 1022 * Optimistic spinning failed, proceed to the slowpath 1023 * and block until we can acquire the sem. 1024 */ 1025 waiter.task = current; 1026 waiter.type = RWSEM_WAITING_FOR_WRITE; 1027 waiter.timeout = jiffies + RWSEM_WAIT_TIMEOUT; 1028 1029 raw_spin_lock_irq(&sem->wait_lock); 1030 1031 /* account for this before adding a new element to the list */ 1032 wstate = list_empty(&sem->wait_list) ? WRITER_FIRST : WRITER_NOT_FIRST; 1033 1034 list_add_tail(&waiter.list, &sem->wait_list); 1035 1036 /* we're now waiting on the lock */ 1037 if (wstate == WRITER_NOT_FIRST) { 1038 count = atomic_long_read(&sem->count); 1039 1040 /* 1041 * If there were already threads queued before us and: 1042 * 1) there are no no active locks, wake the front 1043 * queued process(es) as the handoff bit might be set. 1044 * 2) there are no active writers and some readers, the lock 1045 * must be read owned; so we try to wake any read lock 1046 * waiters that were queued ahead of us. 1047 */ 1048 if (count & RWSEM_WRITER_MASK) 1049 goto wait; 1050 1051 rwsem_mark_wake(sem, (count & RWSEM_READER_MASK) 1052 ? RWSEM_WAKE_READERS 1053 : RWSEM_WAKE_ANY, &wake_q); 1054 1055 if (!wake_q_empty(&wake_q)) { 1056 /* 1057 * We want to minimize wait_lock hold time especially 1058 * when a large number of readers are to be woken up. 1059 */ 1060 raw_spin_unlock_irq(&sem->wait_lock); 1061 wake_up_q(&wake_q); 1062 wake_q_init(&wake_q); /* Used again, reinit */ 1063 raw_spin_lock_irq(&sem->wait_lock); 1064 } 1065 } else { 1066 atomic_long_or(RWSEM_FLAG_WAITERS, &sem->count); 1067 } 1068 1069 wait: 1070 /* wait until we successfully acquire the lock */ 1071 set_current_state(state); 1072 for (;;) { 1073 if (rwsem_try_write_lock(sem, wstate)) { 1074 /* rwsem_try_write_lock() implies ACQUIRE on success */ 1075 break; 1076 } 1077 1078 raw_spin_unlock_irq(&sem->wait_lock); 1079 1080 /* 1081 * After setting the handoff bit and failing to acquire 1082 * the lock, attempt to spin on owner to accelerate lock 1083 * transfer. If the previous owner is a on-cpu writer and it 1084 * has just released the lock, OWNER_NULL will be returned. 1085 * In this case, we attempt to acquire the lock again 1086 * without sleeping. 1087 */ 1088 if (wstate == WRITER_HANDOFF && 1089 rwsem_spin_on_owner(sem) == OWNER_NULL) 1090 goto trylock_again; 1091 1092 /* Block until there are no active lockers. */ 1093 for (;;) { 1094 if (signal_pending_state(state, current)) 1095 goto out_nolock; 1096 1097 schedule(); 1098 lockevent_inc(rwsem_sleep_writer); 1099 set_current_state(state); 1100 /* 1101 * If HANDOFF bit is set, unconditionally do 1102 * a trylock. 1103 */ 1104 if (wstate == WRITER_HANDOFF) 1105 break; 1106 1107 if ((wstate == WRITER_NOT_FIRST) && 1108 (rwsem_first_waiter(sem) == &waiter)) 1109 wstate = WRITER_FIRST; 1110 1111 count = atomic_long_read(&sem->count); 1112 if (!(count & RWSEM_LOCK_MASK)) 1113 break; 1114 1115 /* 1116 * The setting of the handoff bit is deferred 1117 * until rwsem_try_write_lock() is called. 1118 */ 1119 if ((wstate == WRITER_FIRST) && (rt_task(current) || 1120 time_after(jiffies, waiter.timeout))) { 1121 wstate = WRITER_HANDOFF; 1122 lockevent_inc(rwsem_wlock_handoff); 1123 break; 1124 } 1125 } 1126 trylock_again: 1127 raw_spin_lock_irq(&sem->wait_lock); 1128 } 1129 __set_current_state(TASK_RUNNING); 1130 list_del(&waiter.list); 1131 raw_spin_unlock_irq(&sem->wait_lock); 1132 lockevent_inc(rwsem_wlock); 1133 1134 return ret; 1135 1136 out_nolock: 1137 __set_current_state(TASK_RUNNING); 1138 raw_spin_lock_irq(&sem->wait_lock); 1139 list_del(&waiter.list); 1140 1141 if (unlikely(wstate == WRITER_HANDOFF)) 1142 atomic_long_add(-RWSEM_FLAG_HANDOFF, &sem->count); 1143 1144 if (list_empty(&sem->wait_list)) 1145 atomic_long_andnot(RWSEM_FLAG_WAITERS, &sem->count); 1146 else 1147 rwsem_mark_wake(sem, RWSEM_WAKE_ANY, &wake_q); 1148 raw_spin_unlock_irq(&sem->wait_lock); 1149 wake_up_q(&wake_q); 1150 lockevent_inc(rwsem_wlock_fail); 1151 1152 return ERR_PTR(-EINTR); 1153 } 1154 --- 0-DAY CI Kernel Test Service, Intel Corporation https://lists.01.org/hyperkitty/list/kbuild-all@lists.01.org