compiler-rt/test/tsan/fd_dup_norace2.cpp

   1 // RUN: %clangxx_tsan -O1 %s -o %t && %run %t 2>&1 | FileCheck %s
   2 #include "test.h"
   3 #include <sys/types.h>
   4 #include <sys/stat.h>
   5 #include <fcntl.h>
   6 #include <errno.h>
   7
   8 // dup2(oldfd, newfd) races with read(newfd).
   9 // This is not reported as race because:
  10 // 1. Some software dups a closed pipe in place of a socket before closing
  11 //    the socket (to prevent races actually).
  12 // 2. Some daemons dup /dev/null in place of stdin/stdout.
  13
  14 int fd;
  15
  16 void *Thread(void *x) {
  17   char buf;
  18   int n = read(fd, &buf, 1);
  19   if (n != 1) {
  20     // This read can "legitimately" fail regardless of the fact that glibc claims
  21     // that "there is no instant in the middle of calling dup2 at which new is
  22     // closed and not yet a duplicate of old". Strace of the failing runs
  23     // looks as follows:
  24     //
  25     //    [pid 122196] open("/dev/urandom", O_RDONLY) = 3
  26     //    [pid 122196] open("/dev/urandom", O_RDONLY) = 4
  27     //    Process 122382 attached
  28     //    [pid 122382] read(3,  <unfinished ...>
  29     //    [pid 122196] dup2(4, 3 <unfinished ...>
  30     //    [pid 122382] <... read resumed> 0x7fcd139960b7, 1) = -1 EBADF (Bad file descriptor)
  31     //    [pid 122196] <... dup2 resumed> )       = 3
  32     //    read failed: n=-1 errno=9
  33     //
  34     // The failing read does not interfere with what this test tests,
  35     // so we just ignore the failure.
  36     //
  37     // exit(printf("read failed: n=%d errno=%d\n", n, errno));
  38   }
  39   return 0;
  40 }
  41
  42 int main() {
  43   fd = open("/dev/urandom", O_RDONLY);
  44   int fd2 = open("/dev/urandom", O_RDONLY);
  45   if (fd == -1 || fd2 == -1)
  46     exit(printf("open failed\n"));
  47   pthread_t th;
  48   pthread_create(&th, 0, Thread, 0);
  49   if (dup2(fd2, fd) == -1)
  50     exit(printf("dup2 failed\n"));
  51   pthread_join(th, 0);
  52   if (close(fd) == -1)
  53     exit(printf("close failed\n"));
  54   if (close(fd2) == -1)
  55     exit(printf("close failed\n"));
  56   fprintf(stderr, "DONE\n");
  57 }
  58
  59 // CHECK-NOT: WARNING: ThreadSanitizer: data race
  60 // CHECK: DONE