Add FD exhaustion logging for Chrome OS.

base/memory/shared_memory_helper.cc

Index: base/memory/shared_memory_helper.cc
diff --git a/base/memory/shared_memory_helper.cc b/base/memory/shared_memory_helper.cc
index e80083cf78d4e26550c6c9ff99b48f12e8087d1b..4f7c3b5a2058f36269ce3792b7b88d4cc64c17a4 100644
--- a/base/memory/shared_memory_helper.cc
+++ b/base/memory/shared_memory_helper.cc
@@ -4,6 +4,13 @@
 
 #include "base/memory/shared_memory_helper.h"
 
+#if defined(OS_CHROMEOS)
+#include <sys/resource.h>
+#include <sys/time.h>
+
+#include "base/debug/alias.h"
+#endif  // defined(OS_CHROMEOS)
+
 #include "base/threading/thread_restrictions.h"
 
 namespace base {
@@ -90,6 +97,55 @@ bool PrepareMapFile(ScopedFILE fp,
   *mapped_file = HANDLE_EINTR(dup(fileno(fp.get())));
   if (*mapped_file == -1) {
     NOTREACHED() << "Call to dup failed, errno=" << errno;
+#if defined(OS_CHROMEOS)
+    if (errno == EMFILE) {
+      // We're out of file descriptors and are probably about to crash somewhere
+      // else in Chrome anyway. Let's collect what FD information we can and
+      // crash.
+      // Added for debugging crbug.com/733718
+      struct rlimit rlim;
+      if (getrlimit(RLIMIT_NOFILE, &rlim) == 0) {
+        if (rlim.rlim_max > rlim.rlim_cur) {
+          // Increase fd limit so breakpad has a chance to write a minidump.
+          rlim.rlim_cur = rlim.rlim_max;
+          if (setrlimit(RLIMIT_NOFILE, &rlim) != 0) {
+            PLOG(ERROR) << "setrlimit() failed";
+          }
+        }
+      } else {
+        PLOG(ERROR) << "getrlimit() failed";
+        // Fall back to 16K if we can't call getrlimit().
+        rlim.rlim_cur = 16384;
+      }
+
+      static const char* kFileDataMarker = "FDATA";

[Lei Zhang, 2017/06/29 22:06:29]

Can this be trully const as const char kFileDataMarker[] ?

[teravest, 2017/06/29 22:17:44]

Done.

+      char buf[PATH_MAX];

[Lei Zhang, 2017/06/29 22:06:29]

Declare |buf| and |fd_path| closer to where they are used?

[teravest, 2017/06/29 22:17:44]

This is gross, but I want crash_buffer to be as close to the bottom of the stack
as possible. Hopefully the compiler isn't reordering these too much.

+      char fd_path[PATH_MAX];
+      char crash_buffer[2 * 1024 * 1024];  // 2M
+      char *crash_ptr = crash_buffer;
+      memset(crash_buffer, 0, arraysize(crash_buffer));
+      base::debug::Alias(crash_buffer);
+
+      // Put a marker at the start of our data so we can confirm where it
+      // begins.
+      crash_ptr = strncpy(crash_ptr, kFileDataMarker, strlen(kFileDataMarker));
+      for (int i = 0; i < static_cast<int>(rlim.rlim_cur); i++) {
+        memset(buf, 0, arraysize(buf));
+        memset(fd_path, 0, arraysize(fd_path));
+        sprintf(fd_path, "/proc/self/fd/%d", i, arraysize(fd_path) - 1);

[Lei Zhang, 2017/06/29 22:06:29]

Did you mean to use snprintf() here? I only see "%d" in the format string, but
there are 2 arguments following it. Also, the size argument is in the wrong
place.

[teravest, 2017/06/29 22:17:44]

Fixed.

+        ssize_t count = readlink(fd_path, buf, arraysize(buf) - 1);

[Lei Zhang, 2017/06/29 22:06:28]

Do you care if readlink() fails and returns -1?

[teravest, 2017/06/29 22:17:44]

Hmm. Probably not, but I'll add a log anyway.

+
+        if (crash_ptr + count + 1 < crash_buffer + arraysize(crash_buffer)) {
+          crash_ptr = strncpy(crash_ptr, buf, count + 1);
+        }
+
+        if (count >= 0) {
+          LOG(ERROR) << i << ": " << buf;
+        }
+      }
+      CHECK(false) << "Logged for file descriptor exhaustion, crashing now";

[Lei Zhang, 2017/06/29 22:06:29]

super nitty: I like LOG(FATAL) better when it's actually logging a message. :)

[teravest, 2017/06/29 22:17:44]

Done.

+    }
+#endif  // defined(OS_CHROMEOS)
   }
   *readonly_mapped_file = readonly_fd.release();