tsan: intercept vfork
this fixes obscure false positives see the comments and the test for details llvm-svn: 202400
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@ -1903,6 +1903,23 @@ TSAN_INTERCEPTOR(int, fork, int fake) {
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return pid;
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return pid;
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}
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}
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TSAN_INTERCEPTOR(int, vfork, int fake) {
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// Some programs (e.g. openjdk) call close for all file descriptors
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// in the child process. Under tsan it leads to false positives, because
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// address space is shared, so the parent process also thinks that
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// the descriptors are closed (while they are actually not).
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// This leads to false positives due to missed synchronization.
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// Strictly saying this is undefined behavior, because vfork child is not
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// allowed to call any functions other than exec/exit. But this is what
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// openjdk does, so we want to handle it.
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// We could disable interceptors in the child process. But it's not possible
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// to simply intercept and wrap vfork, because vfork child is not allowed
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// to return from the function that calls vfork, and that's exactly what
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// we would do. So this would require some assembly trickery as well.
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// Instead we simply turn vfork into fork.
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return WRAP(fork)(fake);
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}
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static int OnExit(ThreadState *thr) {
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static int OnExit(ThreadState *thr) {
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int status = Finalize(thr);
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int status = Finalize(thr);
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REAL(fflush)(0);
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REAL(fflush)(0);
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@ -2289,6 +2306,7 @@ void InitializeInterceptors() {
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TSAN_INTERCEPT(munlockall);
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TSAN_INTERCEPT(munlockall);
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TSAN_INTERCEPT(fork);
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TSAN_INTERCEPT(fork);
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TSAN_INTERCEPT(vfork);
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TSAN_INTERCEPT(dlopen);
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TSAN_INTERCEPT(dlopen);
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TSAN_INTERCEPT(dlclose);
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TSAN_INTERCEPT(dlclose);
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TSAN_INTERCEPT(on_exit);
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TSAN_INTERCEPT(on_exit);
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@ -0,0 +1,51 @@
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// RUN: %clangxx_tsan -O1 %s -o %t && %t 2>&1 | FileCheck %s
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#include <pthread.h>
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#include <stdio.h>
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#include <stdlib.h>
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#include <unistd.h>
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#include <sys/types.h>
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int fds[2];
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int X;
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void *Thread1(void *x) {
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X = 42;
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write(fds[1], "a", 1);
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return NULL;
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}
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void *Thread2(void *x) {
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char buf;
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while (read(fds[0], &buf, 1) != 1) {
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}
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X = 43;
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return NULL;
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}
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int main() {
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pipe(fds);
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int pid = vfork();
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if (pid < 0) {
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printf("FAIL to vfork\n");
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exit(1);
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}
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if (pid == 0) { // child
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// Closing of fds must not affect parent process.
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// Strictly saying this is undefined behavior, because vfork child is not
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// allowed to call any functions other than exec/exit. But this is what
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// openjdk does.
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close(fds[0]);
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close(fds[1]);
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_exit(0);
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}
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pthread_t t[2];
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pthread_create(&t[0], NULL, Thread1, NULL);
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pthread_create(&t[1], NULL, Thread2, NULL);
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pthread_join(t[0], NULL);
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pthread_join(t[1], NULL);
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printf("DONE\n");
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}
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// CHECK-NOT: WARNING: ThreadSanitizer: data race
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// CHECK-NOT: FAIL to vfork
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// CHECK: DONE
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