[compiler-rt] 66298e1 - tsan: fix another false positive related to open/close
Dmitry Vyukov via llvm-commits
llvm-commits at lists.llvm.org
Thu Mar 10 08:02:55 PST 2022
Author: Dmitry Vyukov
Date: 2022-03-10T17:02:51+01:00
New Revision: 66298e1c54fcf3f4643528c461f5cf376d27055b
URL: https://github.com/llvm/llvm-project/commit/66298e1c54fcf3f4643528c461f5cf376d27055b
DIFF: https://github.com/llvm/llvm-project/commit/66298e1c54fcf3f4643528c461f5cf376d27055b.diff
LOG: tsan: fix another false positive related to open/close
The false positive fixed by commit f831d6fc80
("tsan: fix false positive during fd close") still happens episodically
on the added more stressful test which does just open/close.
I don't have a coherent explanation as to what exactly happens
but the fix fixes the false positive on this test as well.
The issue may be related to lost writes during asynchronous MADV_DONTNEED.
I've debugged similar unexplainable false positive related to freed and
reused memory and at the time the only possible explanation I found is that
an asynchronous MADV_DONTNEED may lead to lost writes. That's why commit
302ec7b9bc ("tsan: add memory_limit_mb flag") added StopTheWorld around
the memory flush, but unfortunately the commit does not capture these findings.
Reviewed By: melver
Differential Revision: https://reviews.llvm.org/D121363
Added:
compiler-rt/test/tsan/fd_close_norace3.cpp
Modified:
compiler-rt/lib/tsan/rtl/tsan_fd.cpp
Removed:
################################################################################
diff --git a/compiler-rt/lib/tsan/rtl/tsan_fd.cpp b/compiler-rt/lib/tsan/rtl/tsan_fd.cpp
index 6c5835fbdc109..9f358eabd21c8 100644
--- a/compiler-rt/lib/tsan/rtl/tsan_fd.cpp
+++ b/compiler-rt/lib/tsan/rtl/tsan_fd.cpp
@@ -113,12 +113,17 @@ static void init(ThreadState *thr, uptr pc, int fd, FdSync *s,
}
d->creation_tid = thr->tid;
d->creation_stack = CurrentStackId(thr, pc);
+ // This prevents false positives on fd_close_norace3.cpp test.
+ // The mechanics of the false positive are not completely clear,
+ // but it happens only if global reset is enabled (flush_memory_ms=1)
+ // and may be related to lost writes during asynchronous MADV_DONTNEED.
+ SlotLocker locker(thr);
if (write) {
// To catch races between fd usage and open.
MemoryRangeImitateWrite(thr, pc, (uptr)d, 8);
} else {
// See the dup-related comment in FdClose.
- MemoryAccess(thr, pc, (uptr)d, 8, kAccessRead);
+ MemoryAccess(thr, pc, (uptr)d, 8, kAccessRead | kAccessSlotLocked);
}
}
diff --git a/compiler-rt/test/tsan/fd_close_norace3.cpp b/compiler-rt/test/tsan/fd_close_norace3.cpp
new file mode 100644
index 0000000000000..eab8cd515ab3e
--- /dev/null
+++ b/compiler-rt/test/tsan/fd_close_norace3.cpp
@@ -0,0 +1,28 @@
+// RUN: %clangxx_tsan -O1 %s -o %t && %env_tsan_opts=flush_memory_ms=1 %run %t 2>&1 | FileCheck %s
+#include "test.h"
+#include <fcntl.h>
+#include <sys/stat.h>
+#include <sys/types.h>
+#include <unistd.h>
+
+void *Thread(void *stop) {
+ while (!__atomic_load_n((int *)stop, __ATOMIC_RELAXED))
+ close(open("/dev/null", O_RDONLY));
+ return 0;
+}
+
+int main() {
+ int stop = 0;
+ const int kThreads = 10;
+ pthread_t th[kThreads];
+ for (int i = 0; i < kThreads; i++)
+ pthread_create(&th[i], 0, Thread, &stop);
+ sleep(5);
+ __atomic_store_n(&stop, 1, __ATOMIC_RELAXED);
+ for (int i = 0; i < kThreads; i++)
+ pthread_join(th[i], 0);
+ fprintf(stderr, "DONE\n");
+}
+
+// CHECK-NOT: WARNING: ThreadSanitizer: data race
+// CHECK: DONE
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