build/build-clang/tsan-hang-be41a98ac222_clang_10.patch

   1 From be41a98ac222f33ed5558d86e1cede67249e99b5 Mon Sep 17 00:00:00 2001
   2 From: Dmitry Vyukov <dvyukov@google.com>
   3 Date: Sat, 21 Mar 2020 13:34:50 +0100
   4 Subject: [PATCH] tsan: fix deadlock with pthread_atfork callbacks
   5
   6 This fixes the bug reported at:
   7 https://groups.google.com/forum/#!topic/thread-sanitizer/e_zB9gYqFHM
   8
   9 A pthread_atfork callback triggers a data race
  10 and we deadlock on the report_mtx. Ignore memory access
  11 in the pthread_atfork callbacks to prevent the deadlock.
  12 ---
  13  compiler-rt/lib/tsan/rtl/tsan_rtl.cc          |  9 ++++
  14  .../test/tsan/pthread_atfork_deadlock2.c      | 49 +++++++++++++++++++
  15  2 files changed, 58 insertions(+)
  16  create mode 100644 compiler-rt/test/tsan/pthread_atfork_deadlock2.c
  17
  18 diff --git a/compiler-rt/lib/tsan/rtl/tsan_rtl.cpp b/compiler-rt/lib/tsan/rtl/tsan_rtl.cpp
  19 index 3f3c0cce119..5e324a0a5fd 100644
  20 --- a/compiler-rt/lib/tsan/rtl/tsan_rtl.cpp
  21 +++ b/compiler-rt/lib/tsan/rtl/tsan_rtl.cpp
  22 @@ -494,14 +494,23 @@ int Finalize(ThreadState *thr) {
  23  void ForkBefore(ThreadState *thr, uptr pc) {
  24    ctx->thread_registry->Lock();
  25    ctx->report_mtx.Lock();
  26 +  // Ignore memory accesses in the pthread_atfork callbacks.
  27 +  // If any of them triggers a data race we will deadlock
  28 +  // on the report_mtx.
  29 +  // We could ignore interceptors and sync operations as well,
  30 +  // but so far it's unclear if it will do more good or harm.
  31 +  // Unnecessarily ignoring things can lead to false positives later.
  32 +  ThreadIgnoreBegin(thr, pc);
  33  }
  34
  35  void ForkParentAfter(ThreadState *thr, uptr pc) {
  36 +  ThreadIgnoreEnd(thr, pc);  // Begin is in ForkBefore.
  37    ctx->report_mtx.Unlock();
  38    ctx->thread_registry->Unlock();
  39  }
  40
  41  void ForkChildAfter(ThreadState *thr, uptr pc) {
  42 +  ThreadIgnoreEnd(thr, pc);  // Begin is in ForkBefore.
  43    ctx->report_mtx.Unlock();
  44    ctx->thread_registry->Unlock();
  45
  46 diff --git a/compiler-rt/test/tsan/pthread_atfork_deadlock2.c b/compiler-rt/test/tsan/pthread_atfork_deadlock2.c
  47 new file mode 100644
  48 index 00000000000..700507c1e63
  49 --- /dev/null
  50 +++ b/compiler-rt/test/tsan/pthread_atfork_deadlock2.c
  51 @@ -0,0 +1,49 @@
  52 +// RUN: %clang_tsan -O1 %s -o %t && %run %t 2>&1 | FileCheck %s
  53 +// Regression test for
  54 +// https://groups.google.com/d/msg/thread-sanitizer/e_zB9gYqFHM/DmAiTsrLAwAJ
  55 +// pthread_atfork() callback triggers a data race and we deadlocked
  56 +// on the report_mtx as we lock it around fork.
  57 +#include "test.h"
  58 +#include <sys/types.h>
  59 +#include <sys/wait.h>
  60 +#include <errno.h>
  61 +
  62 +int glob = 0;
  63 +
  64 +void *worker(void *unused) {
  65 +  glob++;
  66 +  barrier_wait(&barrier);
  67 +  return NULL;
  68 +}
  69 +
  70 +void atfork() {
  71 +  glob++;
  72 +}
  73 +
  74 +int main() {
  75 +  barrier_init(&barrier, 2);
  76 +  pthread_atfork(atfork, NULL, NULL);
  77 +  pthread_t t;
  78 +  pthread_create(&t, NULL, worker, NULL);
  79 +  barrier_wait(&barrier);
  80 +  pid_t pid = fork();
  81 +  if (pid < 0) {
  82 +    fprintf(stderr, "fork failed: %d\n", errno);
  83 +    return 1;
  84 +  }
  85 +  if (pid == 0) {
  86 +    fprintf(stderr, "CHILD\n");
  87 +    return 0;
  88 +  }
  89 +  if (pid != waitpid(pid, NULL, 0)) {
  90 +    fprintf(stderr, "waitpid failed: %d\n", errno);
  91 +    return 1;
  92 +  }
  93 +  pthread_join(t, NULL);
  94 +  fprintf(stderr, "PARENT\n");
  95 +  return 0;
  96 +}
  97 +
  98 +// CHECK-NOT: ThreadSanitizer: data race
  99 +// CHECK: CHILD
 100 +// CHECK: PARENT