--- a/src/os/linux/vm/os_linux.cpp	Wed Feb 19 21:08:04 2014 +0000
+++ b/src/os/linux/vm/os_linux.cpp	Mon Mar 10 22:26:05 2014 +0000
@@ -2861,6 +2861,53 @@
   return res  != (uintptr_t) MAP_FAILED;
 }
 
+static
+address get_stack_commited_bottom(address bottom, size_t size) {
+  address nbot = bottom;
+  address ntop = bottom + size;
+
+  size_t page_sz = os::vm_page_size();
+  unsigned pages = size / page_sz;
+
+  unsigned char vec[1];
+  unsigned imin = 1, imax = pages + 1, imid;
+  int mincore_return_value;
+
+  while (imin < imax) {
+    imid = (imax + imin) / 2;
+    nbot = ntop - (imid * page_sz);
+
+    // Use a trick with mincore to check whether the page is mapped or not.
+    // mincore sets vec to 1 if page resides in memory and to 0 if page
+    // is swapped output but if page we are asking for is unmapped
+    // it returns -1,ENOMEM
+    mincore_return_value = mincore(nbot, page_sz, vec);
+
+    if (mincore_return_value == -1) {
+      // Page is not mapped go up
+      // to find first mapped page
+      if (errno != EAGAIN) {
+        assert(errno == ENOMEM, "Unexpected mincore errno");
+        imax = imid;
+      }
+    } else {
+      // Page is mapped go down
+      // to find first not mapped page
+      imin = imid + 1;
+    }
+  }
+
+  nbot = nbot + page_sz;
+
+  // Adjust stack bottom one page up if last checked page is not mapped
+  if (mincore_return_value == -1) {
+    nbot = nbot + page_sz;
+  }
+
+  return nbot;
+}
+
+
 // Linux uses a growable mapping for the stack, and if the mapping for
 // the stack guard pages is not removed when we detach a thread the
 // stack cannot grow beyond the pages where the stack guard was
@@ -2875,59 +2922,37 @@
 // So, we need to know the extent of the stack mapping when
 // create_stack_guard_pages() is called.
 
-// Find the bounds of the stack mapping.  Return true for success.
-//
 // We only need this for stacks that are growable: at the time of
 // writing thread stacks don't use growable mappings (i.e. those
 // creeated with MAP_GROWSDOWN), and aren't marked "[stack]", so this
 // only applies to the main thread.
 
-static
-bool get_stack_bounds(uintptr_t *bottom, uintptr_t *top) {
-
-  char buf[128];
-  int fd, sz;
-
-  if ((fd = ::open("/proc/self/maps", O_RDONLY)) < 0) {
-    return false;
-  }
-
-  const char kw[] = "[stack]";
-  const int kwlen = sizeof(kw)-1;
-
-  // Address part of /proc/self/maps couldn't be more than 128 bytes
-  while ((sz = os::get_line_chars(fd, buf, sizeof(buf))) > 0) {
-     if (sz > kwlen && ::memcmp(buf+sz-kwlen, kw, kwlen) == 0) {
-        // Extract addresses
-        if (sscanf(buf, "%" SCNxPTR "-%" SCNxPTR, bottom, top) == 2) {
-           uintptr_t sp = (uintptr_t) __builtin_frame_address(0);
-           if (sp >= *bottom && sp <= *top) {
-              ::close(fd);
-              return true;
-           }
-        }
-     }
-  }
-
- ::close(fd);
-  return false;
-}
-
-
 // If the (growable) stack mapping already extends beyond the point
 // where we're going to put our guard pages, truncate the mapping at
 // that point by munmap()ping it.  This ensures that when we later
 // munmap() the guard pages we don't leave a hole in the stack
-// mapping. This only affects the main/initial thread, but guard
-// against future OS changes
+// mapping. This only affects the main/initial thread
+
 bool os::create_stack_guard_pages(char* addr, size_t size) {
-  uintptr_t stack_extent, stack_base;
-  bool chk_bounds = NOT_DEBUG(os::Linux::is_initial_thread()) DEBUG_ONLY(true);
-  if (chk_bounds && get_stack_bounds(&stack_extent, &stack_base)) {
-      assert(os::Linux::is_initial_thread(),
-           "growable stack in non-initial thread");
-    if (stack_extent < (uintptr_t)addr)
-      ::munmap((void*)stack_extent, (uintptr_t)addr - stack_extent);
+
+  if (os::Linux::is_initial_thread()) {
+    // As we manually grow stack up to bottom inside create_attached_thread(),
+    // it's likely that os::Linux::initial_thread_stack_bottom is mapped and
+    // we don't need to do anything special.
+    // Check it first, before calling heavy function.
+    uintptr_t stack_extent = (uintptr_t) os::Linux::initial_thread_stack_bottom();
+    unsigned char vec[1];
+
+    if (mincore((address)stack_extent, os::vm_page_size(), vec) == -1) {
+      // Fallback to slow path on all errors, including EAGAIN
+      stack_extent = (uintptr_t) get_stack_commited_bottom(
+                                    os::Linux::initial_thread_stack_bottom(),
+                                    (size_t)addr - stack_extent);
+    }
+
+    if (stack_extent < (uintptr_t)addr) {
+      ::munmap((void*)stack_extent, (uintptr_t)(addr - stack_extent));
+    }
   }
 
   return os::commit_memory(addr, size, !ExecMem);
@@ -2936,13 +2961,13 @@
 // If this is a growable mapping, remove the guard pages entirely by
 // munmap()ping them.  If not, just call uncommit_memory(). This only
 // affects the main/initial thread, but guard against future OS changes
+// It's safe to always unmap guard pages for initial thread because we
+// always place it right after end of the mapped region
+
 bool os::remove_stack_guard_pages(char* addr, size_t size) {
   uintptr_t stack_extent, stack_base;
-  bool chk_bounds = NOT_DEBUG(os::Linux::is_initial_thread()) DEBUG_ONLY(true);
-  if (chk_bounds && get_stack_bounds(&stack_extent, &stack_base)) {
-      assert(os::Linux::is_initial_thread(),
-           "growable stack in non-initial thread");
-
+
+  if (os::Linux::is_initial_thread()) {
     return ::munmap(addr, size) == 0;
   }
 

--- a/src/share/vm/runtime/os.cpp	Wed Feb 19 21:08:04 2014 +0000
+++ b/src/share/vm/runtime/os.cpp	Mon Mar 10 22:26:05 2014 +0000
@@ -1329,40 +1329,3 @@
   return result;
 }
 
-// Read file line by line, if line is longer than bsize,
-// skip rest of line.
-int os::get_line_chars(int fd, char* buf, const size_t bsize){
-  size_t sz, i = 0;
-
-  // read until EOF, EOL or buf is full
-  while ((sz = (int) read(fd, &buf[i], 1)) == 1 && i < (bsize-2) && buf[i] != '\n') {
-     ++i;
-  }
-
-  if (buf[i] == '\n') {
-    // EOL reached so ignore EOL character and return
-
-    buf[i] = 0;
-    return (int) i;
-  }
-
-  buf[i+1] = 0;
-
-  if (sz != 1) {
-    // EOF reached. if we read chars before EOF return them and
-    // return EOF on next call otherwise return EOF
-
-    return (i == 0) ? -1 : (int) i;
-  }
-
-  // line is longer than size of buf, skip to EOL
-  char ch;
-  while (read(fd, &ch, 1) == 1 && ch != '\n') {
-    // Do nothing
-  }
-
-  // return initial part of line that fits in buf.
-  // If we reached EOF, it will be returned on next call.
-
-  return (int) i;
-}

--- a/src/share/vm/runtime/os.hpp	Wed Feb 19 21:08:04 2014 +0000
+++ b/src/share/vm/runtime/os.hpp	Mon Mar 10 22:26:05 2014 +0000
@@ -683,10 +683,6 @@
   // Hook for os specific jvm options that we don't want to abort on seeing
   static bool obsolete_option(const JavaVMOption *option);
 
-  // Read file line by line. If line is longer than bsize,
-  // rest of line is skipped. Returns number of bytes read or -1 on EOF
-  static int get_line_chars(int fd, char *buf, const size_t bsize);
-
   // Extensions
 #include "runtime/os_ext.hpp"