diff --git a/libc/bionic/pthread_debug.c b/libc/bionic/pthread_debug.c
new file mode 100644
index 0000000..7ee208c
--- /dev/null
+++ b/libc/bionic/pthread_debug.c
@@ -0,0 +1,903 @@
+/*
+ * Copyright (C) 2011 The Android Open Source Project
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ *  * Redistributions of source code must retain the above copyright
+ *    notice, this list of conditions and the following disclaimer.
+ *  * Redistributions in binary form must reproduce the above copyright
+ *    notice, this list of conditions and the following disclaimer in
+ *    the documentation and/or other materials provided with the
+ *    distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+ * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+ * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
+ * FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
+ * COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
+ * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
+ * BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS
+ * OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED
+ * AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
+ * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
+ * OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
+ * SUCH DAMAGE.
+ */
+
+#include <sys/types.h>
+#include <sys/atomics.h>
+#include <sys/system_properties.h>
+#include <sys/mman.h>
+
+#if HAVE_DLADDR
+#include <dlfcn.h>
+#endif
+#include <stdint.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <errno.h>
+#include <pthread.h>
+#include <unwind.h>
+#include <unistd.h>
+
+#include "logd.h"
+#include "bionic_tls.h"
+
+/*
+ * ===========================================================================
+ *      Deadlock prediction
+ * ===========================================================================
+ */
+/*
+The idea is to predict the possibility of deadlock by recording the order
+in which locks are acquired.  If we see an attempt to acquire a lock
+out of order, we can identify the locks and offending code.
+
+To make this work, we need to keep track of the locks held by each thread,
+and create history trees for each lock.  When a thread tries to acquire
+a new lock, we walk through the "history children" of the lock, looking
+for a match with locks the thread already holds.  If we find a match,
+it means the thread has made a request that could result in a deadlock.
+
+To support recursive locks, we always allow re-locking a currently-held
+lock, and maintain a recursion depth count.
+
+An ASCII-art example, where letters represent locks:
+
+        A
+       /|\
+      / | \
+     B  |  D
+      \ |
+       \|
+        C
+
+The above is the tree we'd have after handling lock synchronization
+sequences "ABC", "AC", "AD".  A has three children, {B, C, D}.  C is also
+a child of B.  (The lines represent pointers between parent and child.
+Every node can have multiple parents and multiple children.)
+
+If we hold AC, and want to lock B, we recursively search through B's
+children to see if A or C appears.  It does, so we reject the attempt.
+(A straightforward way to implement it: add a link from C to B, then
+determine whether the graph starting at B contains a cycle.)
+
+If we hold AC and want to lock D, we would succeed, creating a new link
+from C to D.
+
+Updates to MutexInfo structs are only allowed for the thread that holds
+the lock, so we actually do most of our deadlock prediction work after
+the lock has been acquired.
+*/
+
+// =============================================================================
+// log functions
+// =============================================================================
+
+#define LOGD(format, ...)  \
+    __libc_android_log_print(ANDROID_LOG_DEBUG, \
+            "pthread_debug", (format), ##__VA_ARGS__ )
+
+#define LOGW(format, ...)  \
+    __libc_android_log_print(ANDROID_LOG_WARN, \
+            "pthread_debug", (format), ##__VA_ARGS__ )
+
+#define LOGE(format, ...)  \
+    __libc_android_log_print(ANDROID_LOG_ERROR, \
+            "pthread_debug", (format), ##__VA_ARGS__ )
+
+#define LOGI(format, ...)  \
+    __libc_android_log_print(ANDROID_LOG_INFO, \
+            "pthread_debug", (format), ##__VA_ARGS__ )
+
+static const char* const kStartBanner =
+        "===============================================================";
+
+static const char* const kEndBanner =
+        "===============================================================";
+
+extern char* __progname;
+
+// =============================================================================
+// map info functions
+// =============================================================================
+
+typedef struct mapinfo {
+    struct mapinfo *next;
+    unsigned start;
+    unsigned end;
+    char name[];
+} mapinfo;
+
+static mapinfo* sMapInfo = NULL;
+
+static mapinfo *parse_maps_line(char *line)
+{
+    mapinfo *mi;
+    int len = strlen(line);
+
+    if(len < 1) return 0;
+    line[--len] = 0;
+
+    if(len < 50) return 0;
+    if(line[20] != 'x') return 0;
+
+    mi = malloc(sizeof(mapinfo) + (len - 47));
+    if(mi == 0) return 0;
+
+    mi->start = strtoul(line, 0, 16);
+    mi->end = strtoul(line + 9, 0, 16);
+    /* To be filled in parse_elf_info if the mapped section starts with
+     * elf_header
+     */
+    mi->next = 0;
+    strcpy(mi->name, line + 49);
+
+    return mi;
+}
+
+static mapinfo *init_mapinfo(int pid)
+{
+    struct mapinfo *milist = NULL;
+    char data[1024];
+    sprintf(data, "/proc/%d/maps", pid);
+    FILE *fp = fopen(data, "r");
+    if(fp) {
+        while(fgets(data, sizeof(data), fp)) {
+            mapinfo *mi = parse_maps_line(data);
+            if(mi) {
+                mi->next = milist;
+                milist = mi;
+            }
+        }
+        fclose(fp);
+    }
+
+    return milist;
+}
+
+static void deinit_mapinfo(mapinfo *mi)
+{
+   mapinfo *del;
+   while(mi) {
+       del = mi;
+       mi = mi->next;
+       free(del);
+   }
+}
+
+/* Find the containing map info for the pc */
+static const mapinfo *pc_to_mapinfo(mapinfo *mi, unsigned pc, unsigned *rel_pc)
+{
+    *rel_pc = pc;
+    while(mi) {
+        if((pc >= mi->start) && (pc < mi->end)){
+            // Only calculate the relative offset for shared libraries
+            if (strstr(mi->name, ".so")) {
+                *rel_pc -= mi->start;
+            }
+            return mi;
+        }
+        mi = mi->next;
+    }
+    return NULL;
+}
+
+// =============================================================================
+// stack trace functions
+// =============================================================================
+
+#define STACK_TRACE_DEPTH 16
+
+typedef struct
+{
+    size_t count;
+    intptr_t* addrs;
+} stack_crawl_state_t;
+
+/* depends how the system includes define this */
+#ifdef HAVE_UNWIND_CONTEXT_STRUCT
+typedef struct _Unwind_Context __unwind_context;
+#else
+typedef _Unwind_Context __unwind_context;
+#endif
+
+static _Unwind_Reason_Code trace_function(__unwind_context *context, void *arg)
+{
+    stack_crawl_state_t* state = (stack_crawl_state_t*)arg;
+    if (state->count) {
+        intptr_t ip = (intptr_t)_Unwind_GetIP(context);
+        if (ip) {
+            state->addrs[0] = ip;
+            state->addrs++;
+            state->count--;
+            return _URC_NO_REASON;
+        }
+    }
+    /*
+     * If we run out of space to record the address or 0 has been seen, stop
+     * unwinding the stack.
+     */
+    return _URC_END_OF_STACK;
+}
+
+static inline
+int get_backtrace(intptr_t* addrs, size_t max_entries)
+{
+    stack_crawl_state_t state;
+    state.count = max_entries;
+    state.addrs = (intptr_t*)addrs;
+    _Unwind_Backtrace(trace_function, (void*)&state);
+    return max_entries - state.count;
+}
+
+static void log_backtrace(intptr_t* addrs, size_t c)
+{
+    int index = 0;
+    size_t i;
+    for (i=0 ; i<c; i++) {
+        unsigned int relpc;
+        void* offset = 0;
+        const char* symbol = NULL;
+
+#if HAVE_DLADDR
+        Dl_info info;
+        if (dladdr((void*)addrs[i], &info)) {
+            offset = info.dli_saddr;
+            symbol = info.dli_sname;
+        }
+#endif
+
+        if (symbol || index>0 || !HAVE_DLADDR) {
+            /*
+             * this test is a bit sketchy, but it allows us to skip the
+             * stack trace entries due to this debugging code. it works
+             * because those don't have a symbol (they're not exported)
+             */
+            mapinfo const* mi = pc_to_mapinfo(sMapInfo, addrs[i], &relpc);
+            char const* soname = mi ? mi->name : NULL;
+#if HAVE_DLADDR
+            if (!soname)
+                soname = info.dli_fname;
+#endif
+            if (!soname)
+                soname = "unknown";
+
+            if (symbol) {
+                LOGW("          "
+                     "#%02d  pc %08lx  %s (%s+0x%x)",
+                     index, relpc, soname, symbol,
+                     addrs[i] - (intptr_t)offset);
+            } else {
+                LOGW("          "
+                     "#%02d  pc %08lx  %s",
+                     index, relpc, soname);
+            }
+            index++;
+        }
+    }
+}
+
+/****************************************************************************/
+
+/*
+ * level <= 0 : deadlock prediction disabled
+ * level    1 : deadlock prediction enabled, w/o call stacks
+ * level    2 : deadlock prediction enabled w/ call stacks
+ */
+#define CAPTURE_CALLSTACK 2
+static int sPthreadDebugLevel = 0;
+static pid_t sPthreadDebugDisabledThread = -1;
+static pthread_mutex_t sDbgLock = PTHREAD_MUTEX_INITIALIZER;
+
+/****************************************************************************/
+
+/* some simple/lame malloc replacement
+ * NOT thread-safe and leaks everything
+ */
+
+#define DBG_ALLOC_BLOCK_SIZE PAGESIZE
+static size_t sDbgAllocOffset = DBG_ALLOC_BLOCK_SIZE;
+static char* sDbgAllocPtr = NULL;
+
+static void* DbgAllocLocked(size_t size) {
+    if ((sDbgAllocOffset + size) > DBG_ALLOC_BLOCK_SIZE) {
+        sDbgAllocOffset = 0;
+        sDbgAllocPtr = mmap(NULL, DBG_ALLOC_BLOCK_SIZE, PROT_READ|PROT_WRITE,
+                MAP_ANON | MAP_PRIVATE, 0, 0);
+        if (sDbgAllocPtr == MAP_FAILED) {
+            return NULL;
+        }
+    }
+    void* addr = sDbgAllocPtr + sDbgAllocOffset;
+    sDbgAllocOffset += size;
+    return addr;
+}
+
+static void* debug_realloc(void *ptr, size_t size, size_t old_size) {
+    void* addr = mmap(NULL, size, PROT_READ|PROT_WRITE,
+            MAP_ANON | MAP_PRIVATE, 0, 0);
+    if (addr != MAP_FAILED) {
+        if (ptr) {
+            memcpy(addr, ptr, old_size);
+            munmap(ptr, old_size);
+        }
+    } else {
+        addr = NULL;
+    }
+    return addr;
+}
+
+/*****************************************************************************/
+
+struct MutexInfo;
+
+typedef struct CallStack {
+    intptr_t    depth;
+    intptr_t*   addrs;
+} CallStack;
+
+typedef struct MutexInfo* MutexInfoListEntry;
+typedef struct CallStack  CallStackListEntry;
+
+typedef struct GrowingList {
+    int alloc;
+    int count;
+    union {
+        void*               data;
+        MutexInfoListEntry* list;
+        CallStackListEntry* stack;
+    };
+} GrowingList;
+
+typedef GrowingList MutexInfoList;
+typedef GrowingList CallStackList;
+
+typedef struct MutexInfo {
+    // thread currently holding the lock or 0
+    pid_t               owner;
+
+    // most-recently-locked doubly-linked list
+    struct MutexInfo*   prev;
+    struct MutexInfo*   next;
+
+    // for reentrant locks
+    int                 lockCount;
+    // when looking for loops in the graph, marks visited nodes
+    int                 historyMark;
+    // the actual mutex
+    pthread_mutex_t*    mutex;
+    // list of locks directly acquired AFTER this one in the same thread
+    MutexInfoList       children;
+    // list of locks directly acquired BEFORE this one in the same thread
+    MutexInfoList       parents;
+    // list of call stacks when a new link is established to this lock form its parent
+    CallStackList       stacks;
+    // call stack when this lock was acquired last
+    int                 stackDepth;
+    intptr_t            stackTrace[STACK_TRACE_DEPTH];
+} MutexInfo;
+
+static void growingListInit(GrowingList* list) {
+    list->alloc = 0;
+    list->count = 0;
+    list->data = NULL;
+}
+
+static void growingListAdd(GrowingList* pList, size_t objSize) {
+    if (pList->count == pList->alloc) {
+        size_t oldsize = pList->alloc * objSize;
+        pList->alloc += PAGESIZE / objSize;
+        size_t size = pList->alloc * objSize;
+        pList->data = debug_realloc(pList->data, size, oldsize);
+    }
+    pList->count++;
+}
+
+static void initMutexInfo(MutexInfo* object, pthread_mutex_t* mutex) {
+    object->owner = 0;
+    object->prev = 0;
+    object->next = 0;
+    object->lockCount = 0;
+    object->historyMark = 0;
+    object->mutex = mutex;
+    growingListInit(&object->children);
+    growingListInit(&object->parents);
+    growingListInit(&object->stacks);
+    object->stackDepth = 0;
+}
+
+typedef struct ThreadInfo {
+    pid_t       pid;
+    MutexInfo*  mrl;
+} ThreadInfo;
+
+static void initThreadInfo(ThreadInfo* object, pid_t pid) {
+    object->pid = pid;
+    object->mrl = NULL;
+}
+
+/****************************************************************************/
+
+static MutexInfo* get_mutex_info(pthread_mutex_t *mutex);
+static void mutex_lock_checked(MutexInfo* mrl, MutexInfo* object);
+static void mutex_unlock_checked(MutexInfo* object);
+
+/****************************************************************************/
+
+extern int pthread_mutex_lock_impl(pthread_mutex_t *mutex);
+extern int pthread_mutex_unlock_impl(pthread_mutex_t *mutex);
+
+static int pthread_mutex_lock_unchecked(pthread_mutex_t *mutex) {
+    return pthread_mutex_lock_impl(mutex);
+}
+
+static int pthread_mutex_unlock_unchecked(pthread_mutex_t *mutex) {
+    return pthread_mutex_unlock_impl(mutex);
+}
+
+/****************************************************************************/
+
+static void dup_backtrace(CallStack* stack, int count, intptr_t const* addrs) {
+    stack->depth = count;
+    stack->addrs = DbgAllocLocked(count * sizeof(intptr_t));
+    memcpy(stack->addrs, addrs, count * sizeof(intptr_t));
+}
+
+/****************************************************************************/
+
+static int historyListHas(
+        const MutexInfoList* list, MutexInfo const * obj) {
+    int i;
+    for (i=0; i<list->count; i++) {
+        if (list->list[i] == obj) {
+            return i;
+        }
+    }
+    return -1;
+}
+
+static void historyListAdd(MutexInfoList* pList, MutexInfo* obj) {
+    growingListAdd(pList, sizeof(MutexInfoListEntry));
+    pList->list[pList->count - 1] = obj;
+}
+
+static int historyListRemove(MutexInfoList* pList, MutexInfo* obj) {
+    int i;
+    for (i = pList->count-1; i >= 0; i--) {
+        if (pList->list[i] == obj) {
+            break;
+        }
+    }
+    if (i < 0) {
+        // not found!
+        return 0;
+    }
+
+    if (i != pList->count-1) {
+        // copy the last entry to the new free slot
+        pList->list[i] = pList->list[pList->count-1];
+    }
+    pList->count--;
+    memset(&pList->list[pList->count], 0, sizeof(MutexInfoListEntry));
+    return 1;
+}
+
+static void linkParentToChild(MutexInfo* parent, MutexInfo* child) {
+    historyListAdd(&parent->children, child);
+    historyListAdd(&child->parents, parent);
+}
+
+static void unlinkParentFromChild(MutexInfo* parent, MutexInfo* child) {
+    historyListRemove(&parent->children, child);
+    historyListRemove(&child->parents, parent);
+}
+
+/****************************************************************************/
+
+static void callstackListAdd(CallStackList* pList,
+        int count, intptr_t const* addrs) {
+    growingListAdd(pList, sizeof(CallStackListEntry));
+    dup_backtrace(&pList->stack[pList->count - 1], count, addrs);
+}
+
+/****************************************************************************/
+
+/*
+ * Recursively traverse the object hierarchy starting at "obj".  We mark
+ * ourselves on entry and clear the mark on exit.  If we ever encounter
+ * a marked object, we have a cycle.
+ *
+ * Returns "true" if all is well, "false" if we found a cycle.
+ */
+
+static int traverseTree(MutexInfo* obj, MutexInfo const* objParent)
+{
+    /*
+     * Have we been here before?
+     */
+    if (obj->historyMark) {
+        int stackDepth;
+        intptr_t addrs[STACK_TRACE_DEPTH];
+
+        /* Turn off prediction temporarily in this thread while logging */
+        sPthreadDebugDisabledThread = gettid();
+
+        if (sMapInfo == NULL) {
+            // note: we're protected by sDbgLock
+            sMapInfo = init_mapinfo(getpid());
+        }
+
+        LOGW("%s\n", kStartBanner);
+        LOGW("pid: %d, tid: %d >>> %s <<<", getpid(), gettid(), __progname);
+        LOGW("Illegal lock attempt:\n");
+        LOGW("--- pthread_mutex_t at %p\n", obj->mutex);
+        stackDepth = get_backtrace(addrs, STACK_TRACE_DEPTH);
+        log_backtrace(addrs, stackDepth);
+
+        LOGW("+++ Currently held locks in this thread (in reverse order):");
+        MutexInfo* cur = obj;
+        pid_t ourtid = gettid();
+        int i;
+        for (i=0 ; i<cur->parents.count ; i++) {
+            MutexInfo* parent = cur->parents.list[i];
+            if (parent->owner == ourtid) {
+                LOGW("--- pthread_mutex_t at %p\n", parent->mutex);
+                if (sPthreadDebugLevel >= CAPTURE_CALLSTACK) {
+                    log_backtrace(parent->stackTrace, parent->stackDepth);
+                }
+                cur = parent;
+                break;
+            }
+        }
+
+        LOGW("+++ Earlier, the following lock order (from last to first) was established\n");
+        return 0;
+    }
+
+    obj->historyMark = 1;
+
+    MutexInfoList* pList = &obj->children;
+    int result = 1;
+    int i;
+    for (i = pList->count-1; i >= 0; i--) {
+        MutexInfo* child = pList->list[i];
+        if (!traverseTree(child,  obj)) {
+            LOGW("--- pthread_mutex_t at %p\n", obj->mutex);
+            if (sPthreadDebugLevel >= CAPTURE_CALLSTACK) {
+                int index = historyListHas(&obj->parents, objParent);
+                if ((size_t)index < (size_t)obj->stacks.count) {
+                    log_backtrace(
+                            obj->stacks.stack[index].addrs,
+                            obj->stacks.stack[index].depth);
+                } else {
+                    log_backtrace(
+                            obj->stackTrace,
+                            obj->stackDepth);
+                }
+            }
+            result = 0;
+            break;
+        }
+    }
+
+    obj->historyMark = 0;
+    return result;
+}
+
+/****************************************************************************/
+
+static void mutex_lock_checked(MutexInfo* mrl, MutexInfo* object)
+{
+    pid_t tid = gettid();
+    if (object->owner == tid) {
+        object->lockCount++;
+        return;
+    }
+
+    object->owner = tid;
+    object->lockCount = 0;
+
+    if (sPthreadDebugLevel >= CAPTURE_CALLSTACK) {
+        // always record the call stack when acquiring a lock.
+        // it's not efficient, but is useful during diagnostics
+        object->stackDepth = get_backtrace(object->stackTrace, STACK_TRACE_DEPTH);
+    }
+
+    // no other locks held in this thread -- no deadlock possible!
+    if (mrl == NULL)
+        return;
+
+    // check if the lock we're trying to acquire is a direct descendant of
+    // the most recently locked mutex in this thread, in which case we're
+    // in a good situation -- no deadlock possible
+    if (historyListHas(&mrl->children, object) >= 0)
+        return;
+
+    pthread_mutex_lock_unchecked(&sDbgLock);
+
+    linkParentToChild(mrl, object);
+    if (!traverseTree(object, mrl)) {
+        deinit_mapinfo(sMapInfo);
+        sMapInfo = NULL;
+        LOGW("%s\n", kEndBanner);
+        unlinkParentFromChild(mrl, object);
+        // reenable pthread debugging for this thread
+        sPthreadDebugDisabledThread = -1;
+    } else {
+        // record the call stack for this link
+        // NOTE: the call stack is added at the same index
+        // as mrl in object->parents[]
+        // ie: object->parents.count == object->stacks.count, which is
+        // also the index.
+        if (sPthreadDebugLevel >= CAPTURE_CALLSTACK) {
+            callstackListAdd(&object->stacks,
+                    object->stackDepth, object->stackTrace);
+        }
+    }
+
+    pthread_mutex_unlock_unchecked(&sDbgLock);
+}
+
+static void mutex_unlock_checked(MutexInfo* object)
+{
+    pid_t tid = gettid();
+    if (object->owner == tid) {
+        if (object->lockCount == 0) {
+            object->owner = 0;
+        } else {
+            object->lockCount--;
+        }
+    }
+}
+
+
+// =============================================================================
+// Hash Table functions
+// =============================================================================
+
+/****************************************************************************/
+
+#define HASHTABLE_SIZE      256
+
+typedef struct HashEntry HashEntry;
+struct HashEntry {
+    size_t slot;
+    HashEntry* prev;
+    HashEntry* next;
+    void* data;
+};
+
+typedef struct HashTable HashTable;
+struct HashTable {
+    HashEntry* slots[HASHTABLE_SIZE];
+};
+
+static HashTable sMutexMap;
+static HashTable sThreadMap;
+
+/****************************************************************************/
+
+static uint32_t get_hashcode(void const * key, size_t keySize)
+{
+    uint32_t h = keySize;
+    char const* data = (char const*)key;
+    size_t i;
+    for (i = 0; i < keySize; i++) {
+        h = h * 31 + *data;
+        data++;
+    }
+    return (uint32_t)h;
+}
+
+static size_t get_index(uint32_t h)
+{
+    // We apply this secondary hashing discovered by Doug Lea to defend
+    // against bad hashes.
+    h += ~(h << 9);
+    h ^= (((unsigned int) h) >> 14);
+    h += (h << 4);
+    h ^= (((unsigned int) h) >> 10);
+    return (size_t)h & (HASHTABLE_SIZE - 1);
+}
+
+/****************************************************************************/
+
+static void hashmap_init(HashTable* table) {
+    memset(table, 0, sizeof(HashTable));
+}
+
+static void hashmap_removeEntry(HashTable* table, HashEntry* entry)
+{
+    HashEntry* prev = entry->prev;
+    HashEntry* next = entry->next;
+    if (prev != NULL) entry->prev->next = next;
+    if (next != NULL) entry->next->prev = prev;
+    if (prev == NULL) {
+        // we are the head of the list. set the head to be next
+        table->slots[entry->slot] = entry->next;
+    }
+}
+
+static HashEntry* hashmap_lookup(HashTable* table,
+        void const* key, size_t ksize,
+        int (*equals)(void const* data, void const* key))
+{
+    const uint32_t hash = get_hashcode(key, ksize);
+    const size_t slot = get_index(hash);
+
+    HashEntry* entry = table->slots[slot];
+    while (entry) {
+        if (equals(entry->data, key)) {
+            break;
+        }
+        entry = entry->next;
+    }
+
+    if (entry == NULL) {
+        // create a new entry
+        entry = (HashEntry*)DbgAllocLocked(sizeof(HashEntry));
+        entry->data = NULL;
+        entry->slot = slot;
+        entry->prev = NULL;
+        entry->next = table->slots[slot];
+        if (entry->next != NULL) {
+            entry->next->prev = entry;
+        }
+        table->slots[slot] = entry;
+    }
+    return entry;
+}
+
+/****************************************************************************/
+
+static int MutexInfo_equals(void const* data, void const* key) {
+    return ((MutexInfo const *)data)->mutex == *(pthread_mutex_t **)key;
+}
+
+static MutexInfo* get_mutex_info(pthread_mutex_t *mutex)
+{
+    pthread_mutex_lock_unchecked(&sDbgLock);
+
+    HashEntry* entry = hashmap_lookup(&sMutexMap,
+            &mutex, sizeof(mutex),
+            &MutexInfo_equals);
+    if (entry->data == NULL) {
+        entry->data = (MutexInfo*)DbgAllocLocked(sizeof(MutexInfo));
+        initMutexInfo(entry->data, mutex);
+    }
+
+    pthread_mutex_unlock_unchecked(&sDbgLock);
+
+    return (MutexInfo *)entry->data;
+}
+
+/****************************************************************************/
+
+static int ThreadInfo_equals(void const* data, void const* key) {
+    return ((ThreadInfo const *)data)->pid == *(pid_t *)key;
+}
+
+static ThreadInfo* get_thread_info(pid_t pid)
+{
+    pthread_mutex_lock_unchecked(&sDbgLock);
+
+    HashEntry* entry = hashmap_lookup(&sThreadMap,
+            &pid, sizeof(pid),
+            &ThreadInfo_equals);
+    if (entry->data == NULL) {
+        entry->data = (ThreadInfo*)DbgAllocLocked(sizeof(ThreadInfo));
+        initThreadInfo(entry->data, pid);
+    }
+
+    pthread_mutex_unlock_unchecked(&sDbgLock);
+
+    return (ThreadInfo *)entry->data;
+}
+
+static void push_most_recently_locked(MutexInfo* mrl) {
+    ThreadInfo* tinfo = get_thread_info(gettid());
+    mrl->next = NULL;
+    mrl->prev = tinfo->mrl;
+    tinfo->mrl = mrl;
+}
+
+static void remove_most_recently_locked(MutexInfo* mrl) {
+    ThreadInfo* tinfo = get_thread_info(gettid());
+    if (mrl->next) {
+        (mrl->next)->prev = mrl->prev;
+    }
+    if (mrl->prev) {
+        (mrl->prev)->next = mrl->next;
+    }
+    if (tinfo->mrl == mrl) {
+        tinfo->mrl = mrl->next;
+    }
+}
+
+static MutexInfo* get_most_recently_locked() {
+    ThreadInfo* tinfo = get_thread_info(gettid());
+    return tinfo->mrl;
+}
+
+/****************************************************************************/
+
+/* pthread_debug_init() is called from libc_init_dynamic() just
+ * after system properties have been initialized
+ */
+
+__LIBC_HIDDEN__
+void pthread_debug_init(void) {
+    char env[PROP_VALUE_MAX];
+    if (__system_property_get("debug.libc.pthread", env)) {
+        int level = atoi(env);
+        if (level) {
+            LOGI("pthread deadlock detection level %d enabled for pid %d (%s)",
+                    level, getpid(), __progname);
+            hashmap_init(&sMutexMap);
+            sPthreadDebugLevel = level;
+        }
+    }
+}
+
+/*
+ * See if we were allowed to grab the lock at this time.  We do it
+ * *after* acquiring the lock, rather than before, so that we can
+ * freely update the MutexInfo struct.  This seems counter-intuitive,
+ * but our goal is deadlock *prediction* not deadlock *prevention*.
+ * (If we actually deadlock, the situation is easy to diagnose from
+ * a thread dump, so there's no point making a special effort to do
+ * the checks before the lock is held.)
+ */
+
+__LIBC_HIDDEN__
+void pthread_debug_mutex_lock_check(pthread_mutex_t *mutex)
+{
+    if (sPthreadDebugLevel == 0) return;
+    // prediction disabled for this thread
+    if (sPthreadDebugDisabledThread == gettid())
+        return;
+    MutexInfo* object = get_mutex_info(mutex);
+    MutexInfo* mrl = get_most_recently_locked();
+    mutex_lock_checked(mrl, object);
+    push_most_recently_locked(object);
+}
+
+/*
+ * pthread_debug_mutex_unlock_check() must be called with the mutex
+ * still held (ie: before calling the real unlock)
+ */
+
+__LIBC_HIDDEN__
+void pthread_debug_mutex_unlock_check(pthread_mutex_t *mutex)
+{
+    if (sPthreadDebugLevel == 0) return;
+    // prediction disabled for this thread
+    if (sPthreadDebugDisabledThread == gettid())
+        return;
+    MutexInfo* object = get_mutex_info(mutex);
+    remove_most_recently_locked(object);
+    mutex_unlock_checked(object);
+}