From b86ff5f6efbed626fee135ae11311569d84b1e15 Mon Sep 17 00:00:00 2001 From: Bryan Chan Date: Mon, 6 Apr 2020 18:43:35 -0400 Subject: [PATCH] [OpenMP] Sync writes to child thread's data before reduction On systems with weak memory consistency, this patch fixes an intermittent crash in the reduction function called by __kmp_hyper_barrier_gather, which suffers from a race on a child thread's data. Reviewed-By: AndreyChurbanov Differential Revision: https://reviews.llvm.org/D77603 --- openmp/runtime/src/kmp_barrier.cpp | 2 ++ 1 file changed, 2 insertions(+) diff --git a/openmp/runtime/src/kmp_barrier.cpp b/openmp/runtime/src/kmp_barrier.cpp index a6d87b5..4aa7a08 100644 --- a/openmp/runtime/src/kmp_barrier.cpp +++ b/openmp/runtime/src/kmp_barrier.cpp @@ -549,6 +549,7 @@ __kmp_hyper_barrier_gather(enum barrier_type bt, kmp_info_t *this_thr, int gtid, if (((tid >> level) & (branch_factor - 1)) != 0) { kmp_int32 parent_tid = tid & ~((1 << (level + branch_bits)) - 1); + KMP_MB(); // Synchronize parent and child threads. KA_TRACE(20, ("__kmp_hyper_barrier_gather: T#%d(%d:%d) releasing T#%d(%d:%d) " "arrived(%p): %llu => %llu\n", @@ -590,6 +591,7 @@ __kmp_hyper_barrier_gather(enum barrier_type bt, kmp_info_t *this_thr, int gtid, kmp_flag_64 c_flag(&child_bar->b_arrived, new_state); c_flag.wait(this_thr, FALSE USE_ITT_BUILD_ARG(itt_sync_obj)); ANNOTATE_BARRIER_END(child_thr); + KMP_MB(); // Synchronize parent and child threads. #if USE_ITT_BUILD && USE_ITT_NOTIFY // Barrier imbalance - write min of the thread time and a child time to // the thread. -- 2.7.4