[sanitizer] Fix log_path behavior with StopTheWorld.

Summary:
Fix race on report_fd/report_fd_pid between the parent process and the
tracer task.

Reviewers: samsonov

Reviewed By: samsonov

CC: llvm-commits, kcc, dvyukov

Differential Revision: http://llvm-reviews.chandlerc.com/D2306

llvm-svn: 196385

compiler-rt/lib/sanitizer_common/sanitizer_common.cc

@@ -42,6 +42,13 @@ char report_path_prefix[sizeof(report_path_prefix)];
 // child thread will be different from |report_fd_pid|.
 uptr report_fd_pid = 0;
 
+// PID of the tracer task in StopTheWorld. It shares the address space with the
+// main process, but has a different PID and thus requires special handling.
+uptr stoptheworld_tracer_pid = 0;
+// Cached pid of parent process - if the parent process dies, we want to keep
+// writing to the same log file.
+uptr stoptheworld_tracer_ppid = 0;
+
 static DieCallbackType DieCallback;
 void SetDieCallback(DieCallbackType callback) {
   DieCallback = callback;

compiler-rt/lib/sanitizer_common/sanitizer_common.h

@@ -136,6 +136,8 @@ extern fd_t report_fd;
 extern bool log_to_file;
 extern char report_path_prefix[4096];
 extern uptr report_fd_pid;
+extern uptr stoptheworld_tracer_pid;
+extern uptr stoptheworld_tracer_ppid;
 
 uptr OpenFile(const char *filename, bool write);
 // Opens the file 'file_name" and reads up to 'max_len' bytes.

compiler-rt/lib/sanitizer_common/sanitizer_posix.cc

@@ -198,10 +198,15 @@ char *FindPathToBinary(const char *name) {
 }
 
 void MaybeOpenReportFile() {
-  if (!log_to_file || (report_fd_pid == internal_getpid())) return;
+  if (!log_to_file) return;
+  uptr pid = internal_getpid();
+  // If in tracer, use the parent's file.
+  if (pid == stoptheworld_tracer_pid)
+    pid = stoptheworld_tracer_ppid;
+  if (report_fd_pid == pid) return;
   InternalScopedBuffer<char> report_path_full(4096);
   internal_snprintf(report_path_full.data(), report_path_full.size(),
-                    "%s.%d", report_path_prefix, internal_getpid());
+                    "%s.%d", report_path_prefix, pid);
   uptr openrv = OpenFile(report_path_full.data(), true);
   if (internal_iserror(openrv)) {
     report_fd = kStderrFd;
@@ -214,7 +219,7 @@ void MaybeOpenReportFile() {
     internal_close(report_fd);
   }
   report_fd = openrv;
-  report_fd_pid = internal_getpid();
+  report_fd_pid = pid;
 }
 
 void RawWrite(const char *buffer) {

compiler-rt/lib/sanitizer_common/sanitizer_stoptheworld_linux_libcdep.cc

@@ -356,6 +356,20 @@ class StopTheWorldScope {
   int process_was_dumpable_;
 };
 
+// When sanitizer output is being redirected to file (i.e. by using log_path),
+// the tracer should write to the parent's log instead of trying to open a new
+// file. Alert the logging code to the fact that we have a tracer.
+struct ScopedSetTracerPID {
+  explicit ScopedSetTracerPID(uptr tracer_pid) {
+    stoptheworld_tracer_pid = tracer_pid;
+    stoptheworld_tracer_ppid = internal_getpid();
+  }
+  ~ScopedSetTracerPID() {
+    stoptheworld_tracer_pid = 0;
+    stoptheworld_tracer_ppid = 0;
+  }
+};
+
 void StopTheWorld(StopTheWorldCallback callback, void *argument) {
   StopTheWorldScope in_stoptheworld;
   // Prepare the arguments for TracerThread.
@@ -379,6 +393,7 @@ void StopTheWorld(StopTheWorldCallback callback, void *argument) {
       Report("Failed spawning a tracer thread (errno %d).\n", local_errno);
     tracer_thread_argument.mutex.Unlock();
   } else {
+    ScopedSetTracerPID scoped_set_tracer_pid(tracer_pid);
     // On some systems we have to explicitly declare that we want to be traced
     // by the tracer thread.
 #ifdef PR_SET_PTRACER