commit 3a40a0000a2051bab284a220ed5dfa6d2978a744
author Christopher Ferris <cferris@google.com> Sat Jul 11 22:47:06 2015 -0700
committer Christopher Ferris <cferris@google.com> Mon Jul 13 13:18:31 2015 -0700
tree 6f03d507355bd6a4f9496fe1e4e9d6e6637552da
parent 147a50d06e1183e3f39f4f6d0fa28748b33d4aa9

Do not hold hash table lock while backtracing.

There is a deadlock if holding the hash table lock while trying to do
a backtrace. Change the code so that the hash table lock is only held
while actually modifying either g_hash_table, or while modifying an
entry from g_hash_table.

Bug: 22423683
(cherry picked from commit 9fee99b06013787054a312449b94115038e2ad7c)

Change-Id: I72173bfe6f824ceaceea625c24e7851b87467135

libc/bionic/malloc_debug_leak.cpp

diff --git a/libc/bionic/malloc_debug_leak.cpp b/libc/bionic/malloc_debug_leak.cpp
index 64f2112..6a46667 100644
--- a/libc/bionic/malloc_debug_leak.cpp
+++ b/libc/bionic/malloc_debug_leak.cpp
@@ -133,8 +133,9 @@
         size |= SIZE_FLAG_ZYGOTE_CHILD;
     }
 
+    // Keep the lock held for as little time as possible to prevent deadlocks.
+    ScopedPthreadMutexLocker locker(&g_hash_table->lock);
     HashEntry* entry = find_entry(g_hash_table, slot, backtrace, numEntries, size);
-
     if (entry != NULL) {
         entry->allocations++;
     } else {
@@ -302,8 +303,6 @@
 
     void* base = g_malloc_dispatch->malloc(size);
     if (base != NULL) {
-        ScopedPthreadMutexLocker locker(&g_hash_table->lock);
-
         uintptr_t backtrace[BACKTRACE_SIZE];
         size_t numEntries = GET_BACKTRACE(backtrace, BACKTRACE_SIZE);
 
@@ -328,8 +327,6 @@
     return;
   }
 
-  ScopedPthreadMutexLocker locker(&g_hash_table->lock);
-
   // check the guard to make sure it is valid
   AllocationEntry* header = to_header(mem);
 
@@ -342,6 +339,7 @@
     }
   }
 
+  ScopedPthreadMutexLocker locker(&g_hash_table->lock);
   if (header->guard == GUARD || is_valid_entry(header->entry)) {
     // decrement the allocations
     HashEntry* entry = header->entry;