Update ReadProcMaps() to reflect lack of atomicity when reading /proc/self/maps.

base/debug/proc_maps_linux_unittest.cc

Index: base/debug/proc_maps_linux_unittest.cc
diff --git a/base/debug/proc_maps_linux_unittest.cc b/base/debug/proc_maps_linux_unittest.cc
index 9b7d7dcc4af3419c1ef0078eec4007f3fec804fa..7c2929f212a7ae60d16c5a9282053a541ca302a0 100644
--- a/base/debug/proc_maps_linux_unittest.cc
+++ b/base/debug/proc_maps_linux_unittest.cc
@@ -180,14 +180,7 @@ TEST(ProcMapsTest, Permissions) {
   }
 }
 
-// ProcMapsTest.ReadProcMaps fails under TSan on Linux,
-// see http://crbug.com/258451.
-#if defined(THREAD_SANITIZER)
-#define MAYBE_ReadProcMaps DISABLED_ReadProcMaps
-#else
-#define MAYBE_ReadProcMaps ReadProcMaps
-#endif
-TEST(ProcMapsTest, MAYBE_ReadProcMaps) {
+TEST(ProcMapsTest, ReadProcMaps) {
   std::string proc_maps;
   ASSERT_TRUE(ReadProcMaps(&proc_maps));
 
@@ -238,6 +231,13 @@ TEST(ProcMapsTest, MAYBE_ReadProcMaps) {
   EXPECT_TRUE(found_address);
 }
 
+TEST(ProcMapsTest, ReadProcMapsNonEmptyString) {
+  std::string old_string("I forgot to clear the string");
+  std::string proc_maps(old_string);
+  ASSERT_TRUE(ReadProcMaps(&proc_maps));
+  EXPECT_EQ(std::string::npos, proc_maps.find(old_string));
+}
+

[Mark Mentovai, 2013/09/05 19:25:50]

It’d be good if there was a test that ensured that ReadProcMaps was able to
properly read maps larger than a page so that you know your loop gets exercised
in testing and you can validate that things from the first [and middle] and last
reads show up in the output. I can’t come up with a great way to write that test
case, though. I guess you could mmap a few hundred files and make sure their
paths all show up in ReadProcMaps’ output.

I’m not actually asking you to write this test if you don’t want to, it’s
probably not that important and I’d like to see this code get checked in after
what you’ve been through for it.

[scherkus (not reviewing), 2013/09/05 19:54:51]

Yeah ... I'm inclined to pass as the ReadProcMaps test above should be
sufficient for now.

Debug base_unittests has a ~35KB /proc/self/maps so the loop is being covered.
Also while I was iterating on this CL, the ReadProcMaps test was catching
instances where I screwed up the string sizes 'n offsets.

 TEST(ProcMapsTest, MissingFields) {
   static const char* kTestCases[] = {
     "00400000\n",                               // Missing end + beyond.