Enable IO before reading /proc/self/maps.

base/debug/stack_trace_android.cc

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "base/debug/stack_trace.h"
 
 #include <android/log.h>
 #include <unwind.h>
 
 #include "base/debug/proc_maps_linux.h"
 #include "base/strings/stringprintf.h"
+#include "base/threading/thread_restrictions.h"
 
 namespace {
 
 struct StackCrawlState {
   StackCrawlState(uintptr_t* frames, size_t max_depth)
       : frames(frames),
         frame_count(0),
         max_depth(max_depth),
         have_skipped_self(false) {}
 
@@ skipping 56 matching lines @@
   std::string backtrace = ToString();
   __android_log_write(ANDROID_LOG_ERROR, "chromium", backtrace.c_str());
 }
 
 // NOTE: Native libraries in APKs are stripped before installing. Print out the
 // relocatable address and library names so host computers can use tools to
 // symbolize and demangle (e.g., addr2line, c++filt).
 void StackTrace::OutputToStream(std::ostream* os) const {
   std::string proc_maps;
   std::vector<MappedMemoryRegion> regions;
+  // Allow IO to read /proc/self/maps. Reading this file doesn't hit the disk
+  // since it lives in procfs, and this is currently used to print a stack trace
+  // on fatal log messages in debug builds only. If the restriction is enabled
+  // then it will recursively trigger fatal failures when this enters on the
+  // UI thread.
+  base::ThreadRestrictions::ScopedAllowIO allow_io;
   if (!ReadProcMaps(&proc_maps)) {
     __android_log_write(
         ANDROID_LOG_ERROR, "chromium", "Failed to read /proc/self/maps");
   } else if (!ParseProcMaps(proc_maps, &regions)) {
     __android_log_write(
         ANDROID_LOG_ERROR, "chromium", "Failed to parse /proc/self/maps");
   }
 
   for (size_t i = 0; i < count_; ++i) {
     // Subtract one as return address of function may be in the next
@@ skipping 18 matching lines @@
     } else {
       *os << "<unknown>";
     }
 
     *os << "\n";
   }
 }
 
 }  // namespace debug
 }  // namespace base