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tsan: fix test invisible barrier

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Another attempt at fixing tsan_invisible_barrier.
Current implementation causes:
https://llvm.org/bugs/show_bug.cgi?id=25643

There were several unsuccessful iterations for this functionality:

Initially it was implemented in user code using REAL(pthread_barrier_wait). But pthread_barrier_wait is not supported on MacOS. Futexes are linux-specific for this matter.
Then we switched to atomics+usleep(10). But usleep produced parasitic "as-if synchronized via sleep" messages in reports which failed some output tests.
Then we switched to atomics+sched_yield. But this produced tons of tsan- visible events, which lead to "failed to restore stack trace" failures.
Move implementation into runtime and use internal_sched_yield in the wait loop.
This way tsan should see no events from the barrier, so not trace overflows and
no "as-if synchronized via sleep" messages.

llvm-svn: 255030
This commit is contained in:
Dmitry Vyukov 2015-12-08 17:54:47 +00:00
parent d0edbdfad1
commit eee690b29a
3 changed files with 51 additions and 18 deletions
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36
compiler-rt/lib/tsan/rtl/tsan_interceptors.cc
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@ -2683,3 +2683,39 @@ void InitializeInterceptors() {
}
} // namespace __tsan
// Invisible barrier for tests.
// There were several unsuccessful iterations for this functionality:
// 1. Initially it was implemented in user code using
// REAL(pthread_barrier_wait). But pthread_barrier_wait is not supported on
// MacOS. Futexes are linux-specific for this matter.
// 2. Then we switched to atomics+usleep(10). But usleep produced parasitic
// "as-if synchronized via sleep" messages in reports which failed some
// output tests.
// 3. Then we switched to atomics+sched_yield. But this produced tons of tsan-
// visible events, which lead to "failed to restore stack trace" failures.
// Note that no_sanitize_thread attribute does not turn off atomic interception
// so attaching it to the function defined in user code does not help.
// That's why we now have what we have.
extern "C" SANITIZER_INTERFACE_ATTRIBUTE
void __tsan_testonly_barrier_init(u64 *barrier, u32 count) {
if (count >= (1 << 8)) {
Printf("barrier_init: count is too large (%d)\n", count);
Die();
}
// 8 lsb is thread count, the remaining are count of entered threads.
*barrier = count;
}
extern "C" SANITIZER_INTERFACE_ATTRIBUTE
void __tsan_testonly_barrier_wait(u64 *barrier) {
unsigned old = __atomic_fetch_add(barrier, 1 << 8, __ATOMIC_RELAXED);
unsigned old_epoch = (old >> 8) / (old & 0xff);
for (;;) {
unsigned cur = __atomic_load_n(barrier, __ATOMIC_RELAXED);
unsigned cur_epoch = (cur >> 8) / (cur & 0xff);
if (cur_epoch != old_epoch)
return;
internal_sched_yield();
}
}

2
compiler-rt/test/tsan/load_shared_lib.cc
View File

@ -3,7 +3,7 @@
// symbolized correctly.
// RUN: %clangxx_tsan -O1 %s -DBUILD_SO -fPIC -shared -o %t-so.so
// RUN: %clangxx_tsan -O1 %s -o %t && %deflake %run %t | FileCheck %s
// RUN: %clangxx_tsan -O1 %s -o %t -rdynamic && %deflake %run %t | FileCheck %s
#ifdef BUILD_SO

31
compiler-rt/test/tsan/test.h
View File

@ -14,27 +14,24 @@
// TSan-invisible barrier.
// Tests use it to establish necessary execution order in a way that does not
// interfere with tsan (does not establish synchronization between threads).
// 8 lsb is thread count, the remaining are count of entered threads.
typedef unsigned long long invisible_barrier_t;
void barrier_init(invisible_barrier_t *barrier, unsigned count) {
if (count >= (1 << 8))
exit(fprintf(stderr, "barrier_init: count is too large (%d)\n", count));
*barrier = count;
#ifdef __cplusplus
extern "C" {
#endif
void __tsan_testonly_barrier_init(invisible_barrier_t *barrier,
unsigned count);
void __tsan_testonly_barrier_wait(invisible_barrier_t *barrier);
#ifdef __cplusplus
}
#endif
static inline void barrier_init(invisible_barrier_t *barrier, unsigned count) {
__tsan_testonly_barrier_init(barrier, count);
}
void barrier_wait(invisible_barrier_t *barrier) {
unsigned old = __atomic_fetch_add(barrier, 1 << 8, __ATOMIC_RELAXED);
unsigned old_epoch = (old >> 8) / (old & 0xff);
for (;;) {
unsigned cur = __atomic_load_n(barrier, __ATOMIC_RELAXED);
unsigned cur_epoch = (cur >> 8) / (cur & 0xff);
if (cur_epoch != old_epoch)
return;
// Can't use usleep, because it leads to spurious "As if synchronized via
// sleep" messages which fail some output tests.
sched_yield();
}
static inline void barrier_wait(invisible_barrier_t *barrier) {
__tsan_testonly_barrier_wait(barrier);
}
// Default instance of the barrier, but a test can declare more manually.