Index: lib/asan/asan_allocator.h
===================================================================
--- lib/asan/asan_allocator.h
+++ lib/asan/asan_allocator.h
@@ -213,5 +213,7 @@
 void PrintInternalAllocatorStats();
 void AsanSoftRssLimitExceededCallback(bool exceeded);
 
+AsanAllocator &get_allocator();
+
 }  // namespace __asan
 #endif  // ASAN_ALLOCATOR_H
Index: lib/asan/asan_allocator.cc
===================================================================
--- lib/asan/asan_allocator.cc
+++ lib/asan/asan_allocator.cc
@@ -47,8 +47,6 @@
   return res;
 }
 
-static AsanAllocator &get_allocator();
-
 // The memory chunk allocated from the underlying allocator looks like this:
 // L L L L L L H H U U U U U U R R
 //   L -- left redzone words (0 or more bytes)
@@ -719,7 +717,7 @@
 
 static Allocator instance(LINKER_INITIALIZED);
 
-static AsanAllocator &get_allocator() {
+AsanAllocator &get_allocator() {
   return instance.allocator;
 }
 
Index: lib/asan/asan_interceptors.cc
===================================================================
--- lib/asan/asan_interceptors.cc
+++ lib/asan/asan_interceptors.cc
@@ -22,6 +22,7 @@
 #include "asan_stats.h"
 #include "asan_suppressions.h"
 #include "lsan/lsan_common.h"
+#include "sanitizer_common/sanitizer_stackdepot.h"
 #include "sanitizer_common/sanitizer_libc.h"
 
 #if SANITIZER_POSIX
@@ -711,11 +712,23 @@
 #endif  // ASAN_INTERCEPT___CXA_ATEXIT
 
 #if ASAN_INTERCEPT_FORK
+static void BeforeFork() {
+  StackDepotLockAll();
+  get_allocator().ForceLock();
+}
+
+static void AfterFork() {
+  get_allocator().ForceUnlock();
+  StackDepotUnlockAll();
+}
+
 INTERCEPTOR(int, fork, void) {
   ENSURE_ASAN_INITED();
+  BeforeFork();
   if (common_flags()->coverage) CovBeforeFork();
   int pid = REAL(fork)();
   if (common_flags()->coverage) CovAfterFork(pid);
+  AfterFork();
   return pid;
 }
 #endif  // ASAN_INTERCEPT_FORK
Index: test/asan/TestCases/Linux/fork.cc
===================================================================
--- /dev/null
+++ test/asan/TestCases/Linux/fork.cc
@@ -0,0 +1,109 @@
+// https://github.com/google/sanitizers/issues/774
+// Test that ASans allocator is fork-safe.
+// Run a number of threads that perform memory allocation/deallocation, then fork
+// and verify that malloc/free do not deadlock in the child process.
+
+// RUN: %clangxx_asan -std=c++11 %s -o %t
+// RUN: ASAN_OPTIONS=detect_leaks=0 %run %t 2>&1 | FileCheck %s
+
+// Fun fact: if test output is redirected to a file (as opposed to
+// being piped directly to FileCheck), we may lose some "done"s due to
+// a kernel bug:
+// https://lkml.org/lkml/2014/2/17/324
+
+// Flaky on PPC64.
+// UNSUPPORTED: powerpc64-target-arch
+// UNSUPPORTED: powerpc64le-target-arch
+
+#include <pthread.h>
+#include <unistd.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <sys/types.h>
+#include <sys/wait.h>
+#include <sys/time.h>
+#include <signal.h>
+#include <errno.h>
+
+int done;
+
+void *worker(void *arg) {
+  while (true) {
+    void *p = malloc(1337);
+    free(p);
+    if (__atomic_load_n(&done, __ATOMIC_RELAXED))
+      return 0;
+  }
+  return 0;
+}
+
+// Run through malloc/free in the child process.
+// If any of the hash table cells are locked, this may deadlock.
+// This can also deadlock at allocator cache refilling.
+void child() {
+  for (int i = 0; i < 10000; ++i) {
+    void *p = malloc(1337);
+    free(p);
+  }
+  write(2, "done\n", 5);
+}
+
+void test() {
+  const int kThreads = 10;
+  pthread_t t[kThreads];
+  for (int i = 0; i < kThreads; ++i)
+    pthread_create(&t[i], NULL, worker, (void*)(long)i);
+  usleep(100000);
+  pid_t pid = fork();
+  if (pid) {
+    // parent
+    __atomic_store_n(&done, 1, __ATOMIC_RELAXED);
+    pid_t p;
+    while ((p = wait(NULL)) == -1) {  }
+  } else {
+    // child
+    child();
+  }
+}
+
+int main() {
+  const int kChildren = 20;
+  for (int i = 0; i < kChildren; ++i) {
+    pid_t pid = fork();
+    if (pid) {
+      // parent
+    } else {
+      test();
+      exit(0);
+    }
+  }
+
+  for (int i = 0; i < kChildren; ++i) {
+    pid_t p;
+    while ((p = wait(NULL)) == -1) {  }
+  }
+
+  return 0;
+}
+
+// Expect 20 (== kChildren) "done" messages.
+// CHECK: done
+// CHECK: done
+// CHECK: done
+// CHECK: done
+// CHECK: done
+// CHECK: done
+// CHECK: done
+// CHECK: done
+// CHECK: done
+// CHECK: done
+// CHECK: done
+// CHECK: done
+// CHECK: done
+// CHECK: done
+// CHECK: done
+// CHECK: done
+// CHECK: done
+// CHECK: done
+// CHECK: done
+// CHECK: done