Merge "Fix race condition updating local map data."
diff --git a/debuggerd/tombstone.cpp b/debuggerd/tombstone.cpp
index fa983fa..dfdf29c 100644
--- a/debuggerd/tombstone.cpp
+++ b/debuggerd/tombstone.cpp
@@ -368,6 +368,7 @@
ALOGE("Cannot get siginfo for %d: %s\n", tid, strerror(errno));
}
+ ScopedBacktraceMapIteratorLock lock(map);
_LOG(log, logtype::MAPS, "\n");
if (!print_fault_address_marker) {
_LOG(log, logtype::MAPS, "memory map:\n");
diff --git a/include/backtrace/BacktraceMap.h b/include/backtrace/BacktraceMap.h
index 2373c45..b80045f 100644
--- a/include/backtrace/BacktraceMap.h
+++ b/include/backtrace/BacktraceMap.h
@@ -71,6 +71,12 @@
bool IsWritable(uintptr_t pc) { return GetFlags(pc) & PROT_WRITE; }
bool IsExecutable(uintptr_t pc) { return GetFlags(pc) & PROT_EXEC; }
+ // In order to use the iterators on this object, a caller must
+ // call the LockIterator and UnlockIterator function to guarantee
+ // that the data does not change while it's being used.
+ virtual void LockIterator() {}
+ virtual void UnlockIterator() {}
+
typedef std::deque<backtrace_map_t>::iterator iterator;
iterator begin() { return maps_.begin(); }
iterator end() { return maps_.end(); }
@@ -102,4 +108,18 @@
pid_t pid_;
};
+class ScopedBacktraceMapIteratorLock {
+public:
+ explicit ScopedBacktraceMapIteratorLock(BacktraceMap* map) : map_(map) {
+ map->LockIterator();
+ }
+
+ ~ScopedBacktraceMapIteratorLock() {
+ map_->UnlockIterator();
+ }
+
+private:
+ BacktraceMap* map_;
+};
+
#endif // _BACKTRACE_BACKTRACE_MAP_H
diff --git a/libbacktrace/BacktraceMap.cpp b/libbacktrace/BacktraceMap.cpp
index 19551dc..00c35b1 100644
--- a/libbacktrace/BacktraceMap.cpp
+++ b/libbacktrace/BacktraceMap.cpp
@@ -36,8 +36,8 @@
}
void BacktraceMap::FillIn(uintptr_t addr, backtrace_map_t* map) {
- for (BacktraceMap::const_iterator it = begin();
- it != end(); ++it) {
+ ScopedBacktraceMapIteratorLock lock(this);
+ for (BacktraceMap::const_iterator it = begin(); it != end(); ++it) {
if (addr >= it->start && addr < it->end) {
*map = *it;
return;
diff --git a/libbacktrace/UnwindMap.cpp b/libbacktrace/UnwindMap.cpp
index 34d79f9..af79562 100644
--- a/libbacktrace/UnwindMap.cpp
+++ b/libbacktrace/UnwindMap.cpp
@@ -14,6 +14,7 @@
* limitations under the License.
*/
+#include <pthread.h>
#include <stdint.h>
#include <stdlib.h>
#include <sys/types.h>
@@ -72,6 +73,7 @@
}
UnwindMapLocal::UnwindMapLocal() : UnwindMap(getpid()), map_created_(false) {
+ pthread_rwlock_init(&map_lock_, nullptr);
}
UnwindMapLocal::~UnwindMapLocal() {
@@ -82,9 +84,14 @@
}
bool UnwindMapLocal::GenerateMap() {
+ // Lock so that multiple threads cannot modify the maps data at the
+ // same time.
+ pthread_rwlock_wrlock(&map_lock_);
+
// It's possible for the map to be regenerated while this loop is occurring.
// If that happens, get the map again, but only try at most three times
// before giving up.
+ bool generated = false;
for (int i = 0; i < 3; i++) {
maps_.clear();
@@ -110,12 +117,17 @@
}
// Check to see if the map changed while getting the data.
if (ret != -UNW_EINVAL) {
- return true;
+ generated = true;
+ break;
}
}
- BACK_LOGW("Unable to generate the map.");
- return false;
+ pthread_rwlock_unlock(&map_lock_);
+
+ if (!generated) {
+ BACK_LOGW("Unable to generate the map.");
+ }
+ return generated;
}
bool UnwindMapLocal::Build() {
diff --git a/libbacktrace/UnwindMap.h b/libbacktrace/UnwindMap.h
index 111401f..f85b54a 100644
--- a/libbacktrace/UnwindMap.h
+++ b/libbacktrace/UnwindMap.h
@@ -17,6 +17,7 @@
#ifndef _LIBBACKTRACE_UNWIND_MAP_H
#define _LIBBACKTRACE_UNWIND_MAP_H
+#include <pthread.h>
#include <stdint.h>
#include <sys/types.h>
@@ -56,10 +57,15 @@
void FillIn(uintptr_t addr, backtrace_map_t* map) override;
+ void LockIterator() override { pthread_rwlock_rdlock(&map_lock_); }
+ void UnlockIterator() override { pthread_rwlock_unlock(&map_lock_); }
+
private:
bool GenerateMap();
bool map_created_;
+
+ pthread_rwlock_t map_lock_;
};
#endif // _LIBBACKTRACE_UNWIND_MAP_H
diff --git a/libbacktrace/backtrace_test.cpp b/libbacktrace/backtrace_test.cpp
index 7066c79..e25c8e9 100644
--- a/libbacktrace/backtrace_test.cpp
+++ b/libbacktrace/backtrace_test.cpp
@@ -895,6 +895,7 @@
std::unique_ptr<BacktraceMap> map(BacktraceMap::Create(pid));
// Basic test that verifies that the map is in the expected order.
+ ScopedBacktraceMapIteratorLock lock(map.get());
std::vector<map_test_t>::const_iterator test_it = test_maps.begin();
for (BacktraceMap::const_iterator it = map->begin(); it != map->end(); ++it) {
ASSERT_TRUE(test_it != test_maps.end());