From 7bc300c8fc4d6e1e49cb79af2109a1c05b922772 Mon Sep 17 00:00:00 2001
From: Sergey Matveev <earthdok@google.com>
Date: Wed, 4 Dec 2013 14:37:01 +0000
Subject: [PATCH] [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
---
 .../lib/sanitizer_common/sanitizer_common.cc      |  7 +++++++
 .../lib/sanitizer_common/sanitizer_common.h       |  2 ++
 .../lib/sanitizer_common/sanitizer_posix.cc       | 11 ++++++++---
 .../sanitizer_stoptheworld_linux_libcdep.cc       | 15 +++++++++++++++
 4 files changed, 32 insertions(+), 3 deletions(-)

diff --git a/compiler-rt/lib/sanitizer_common/sanitizer_common.cc b/compiler-rt/lib/sanitizer_common/sanitizer_common.cc
index 7e870ff65455..c156989d9bcd 100644
--- a/compiler-rt/lib/sanitizer_common/sanitizer_common.cc
+++ b/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;
diff --git a/compiler-rt/lib/sanitizer_common/sanitizer_common.h b/compiler-rt/lib/sanitizer_common/sanitizer_common.h
index d29f68cedf9b..ab67be21c05e 100644
--- a/compiler-rt/lib/sanitizer_common/sanitizer_common.h
+++ b/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.
diff --git a/compiler-rt/lib/sanitizer_common/sanitizer_posix.cc b/compiler-rt/lib/sanitizer_common/sanitizer_posix.cc
index 5438aca94688..4d2c033c5abd 100644
--- a/compiler-rt/lib/sanitizer_common/sanitizer_posix.cc
+++ b/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) {
diff --git a/compiler-rt/lib/sanitizer_common/sanitizer_stoptheworld_linux_libcdep.cc b/compiler-rt/lib/sanitizer_common/sanitizer_stoptheworld_linux_libcdep.cc
index a34ddd872209..8a0ffd434e62 100644
--- a/compiler-rt/lib/sanitizer_common/sanitizer_stoptheworld_linux_libcdep.cc
+++ b/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