commit d780dcbaa5986f6e88f812d743d33d17b3f9a8e1
author Colin Cross <ccross@android.com> Tue Nov 27 16:14:53 2018 -0800
committer Colin Cross <ccross@android.com> Tue Nov 27 17:00:56 2018 -0800
tree 2353a8d75f4301b3b8e07805d60011ae8739bc9f
parent 3a2bd498f8703ca7fcd281da25e027ea00833e1c

Reduce logging around segfaults

The excessive logging of pages with segfaults is making it hard to
see what caused the problem, only log the first page that segfaults,
the range that was being walked when the first segfault happened,
and the total number of pages that segfaulted.

Bug: 120032857
Test: memunreachable_test --gtest_filter=HeapWalkerTest.segv
Change-Id: I71821a3f5be65f2fbcb36afc4b7b1ffa4a48e660

libmemunreachable/HeapWalker.cpp

diff --git a/libmemunreachable/HeapWalker.cpp b/libmemunreachable/HeapWalker.cpp
index 2403ad0..a046dad 100644
--- a/libmemunreachable/HeapWalker.cpp
+++ b/libmemunreachable/HeapWalker.cpp
@@ -76,12 +76,14 @@
     Range range = to_do.back();
     to_do.pop_back();
 
+    walking_range_ = range;
     ForEachPtrInRange(range, [&](Range& ref_range, AllocationInfo* ref_info) {
       if (!ref_info->referenced_from_root) {
         ref_info->referenced_from_root = true;
         to_do.push_back(ref_range);
       }
     });
+    walking_range_ = Range{0, 0};
   }
 }
 
@@ -113,6 +115,10 @@
 
   RecurseRoot(vals);
 
+  if (segv_page_count_ > 0) {
+    MEM_ALOGE("%zu pages skipped due to segfaults", segv_page_count_);
+  }
+
   return true;
 }
 
@@ -168,7 +174,15 @@
     handler.reset();
     return;
   }
-  MEM_ALOGW("failed to read page at %p, signal %d", si->si_addr, signal);
+  if (!segv_logged_) {
+    MEM_ALOGW("failed to read page at %p, signal %d", si->si_addr, signal);
+    if (walking_range_.begin != 0U) {
+      MEM_ALOGW("while walking range %p-%p", reinterpret_cast<void*>(walking_range_.begin),
+                reinterpret_cast<void*>(walking_range_.end));
+    }
+    segv_logged_ = true;
+  }
+  segv_page_count_++;
   if (!MapOverPage(si->si_addr)) {
     handler.reset();
   }