1 files changed, 100 insertions, 0 deletions
diff --git a/build/build-clang/tsan-hang-be41a98ac222.patch b/build/build-clang/tsan-hang-be41a98ac222.patch
new file mode 100644
index 0000000000..3e148e52b3
--- /dev/null
+++ b/build/build-clang/tsan-hang-be41a98ac222.patch
@@ -0,0 +1,100 @@
+From be41a98ac222f33ed5558d86e1cede67249e99b5 Mon Sep 17 00:00:00 2001
+From: Dmitry Vyukov <dvyukov@google.com>
+Date: Sat, 21 Mar 2020 13:34:50 +0100
+Subject: [PATCH] tsan: fix deadlock with pthread_atfork callbacks
+
+This fixes the bug reported at:
+https://groups.google.com/forum/#!topic/thread-sanitizer/e_zB9gYqFHM
+
+A pthread_atfork callback triggers a data race
+and we deadlock on the report_mtx. Ignore memory access
+in the pthread_atfork callbacks to prevent the deadlock.
+---
+ compiler-rt/lib/tsan/rtl/tsan_rtl.cc          |  9 ++++
+ .../test/tsan/pthread_atfork_deadlock2.c      | 49 +++++++++++++++++++
+ 2 files changed, 58 insertions(+)
+ create mode 100644 compiler-rt/test/tsan/pthread_atfork_deadlock2.c
+
+diff --git a/compiler-rt/lib/tsan/rtl/tsan_rtl.cc b/compiler-rt/lib/tsan/rtl/tsan_rtl.ccc
+index fe469faad2a2..13c9b770f50a 100644
+--- a/compiler-rt/lib/tsan/rtl/tsan_rtl.cc
++++ b/compiler-rt/lib/tsan/rtl/tsan_rtl.cc
+@@ -495,14 +495,23 @@ int Finalize(ThreadState *thr) {
+ void ForkBefore(ThreadState *thr, uptr pc) {
+   ctx->thread_registry->Lock();
+   ctx->report_mtx.Lock();
++  // Ignore memory accesses in the pthread_atfork callbacks.
++  // If any of them triggers a data race we will deadlock
++  // on the report_mtx.
++  // We could ignore interceptors and sync operations as well,
++  // but so far it's unclear if it will do more good or harm.
++  // Unnecessarily ignoring things can lead to false positives later.
++  ThreadIgnoreBegin(thr, pc);
+ }
+ 
+ void ForkParentAfter(ThreadState *thr, uptr pc) {
++  ThreadIgnoreEnd(thr, pc);  // Begin is in ForkBefore.
+   ctx->report_mtx.Unlock();
+   ctx->thread_registry->Unlock();
+ }
+ 
+ void ForkChildAfter(ThreadState *thr, uptr pc) {
++  ThreadIgnoreEnd(thr, pc);  // Begin is in ForkBefore.
+   ctx->report_mtx.Unlock();
+   ctx->thread_registry->Unlock();
+ 
+diff --git a/compiler-rt/test/tsan/pthread_atfork_deadlock2.c b/compiler-rt/test/tsan/pthread_atfork_deadlock2.c
+new file mode 100644
+index 000000000000..700507c1e637
+--- /dev/null
++++ b/compiler-rt/test/tsan/pthread_atfork_deadlock2.c
+@@ -0,0 +1,49 @@
++// RUN: %clang_tsan -O1 %s -o %t && %run %t 2>&1 | FileCheck %s
++// Regression test for
++// https://groups.google.com/d/msg/thread-sanitizer/e_zB9gYqFHM/DmAiTsrLAwAJ
++// pthread_atfork() callback triggers a data race and we deadlocked
++// on the report_mtx as we lock it around fork.
++#include "test.h"
++#include <sys/types.h>
++#include <sys/wait.h>
++#include <errno.h>
++
++int glob = 0;
++
++void *worker(void *unused) {
++  glob++;
++  barrier_wait(&barrier);
++  return NULL;
++}
++
++void atfork() {
++  glob++;
++}
++
++int main() {
++  barrier_init(&barrier, 2);
++  pthread_atfork(atfork, NULL, NULL);
++  pthread_t t;
++  pthread_create(&t, NULL, worker, NULL);
++  barrier_wait(&barrier);
++  pid_t pid = fork();
++  if (pid < 0) {
++    fprintf(stderr, "fork failed: %d\n", errno);
++    return 1;
++  }
++  if (pid == 0) {
++    fprintf(stderr, "CHILD\n");
++    return 0;
++  }
++  if (pid != waitpid(pid, NULL, 0)) {
++    fprintf(stderr, "waitpid failed: %d\n", errno);
++    return 1;
++  }
++  pthread_join(t, NULL);
++  fprintf(stderr, "PARENT\n");
++  return 0;
++}
++
++// CHECK-NOT: ThreadSanitizer: data race
++// CHECK: CHILD
++// CHECK: PARENT