Merge "Don't use mem cgroups for pid accounting." into nyc-dev
diff --git a/debuggerd/Android.mk b/debuggerd/Android.mk
index 9e4f1f7..6469db4 100644
--- a/debuggerd/Android.mk
+++ b/debuggerd/Android.mk
@@ -15,6 +15,7 @@
     debuggerd.cpp \
     elf_utils.cpp \
     getevent.cpp \
+    signal_sender.cpp \
     tombstone.cpp \
     utility.cpp \
 
diff --git a/debuggerd/debuggerd.cpp b/debuggerd/debuggerd.cpp
index 86d7c14..97f4096 100644
--- a/debuggerd/debuggerd.cpp
+++ b/debuggerd/debuggerd.cpp
@@ -15,21 +15,20 @@
  */
 
 #include <dirent.h>
+#include <elf.h>
 #include <errno.h>
 #include <fcntl.h>
 #include <pthread.h>
 #include <signal.h>
 #include <stdarg.h>
 #include <stdio.h>
-#include <sys/types.h>
-#include <time.h>
-
-#include <elf.h>
 #include <sys/poll.h>
 #include <sys/prctl.h>
 #include <sys/ptrace.h>
 #include <sys/stat.h>
+#include <sys/types.h>
 #include <sys/wait.h>
+#include <time.h>
 
 #include <set>
 
@@ -48,6 +47,7 @@
 
 #include "backtrace.h"
 #include "getevent.h"
+#include "signal_sender.h"
 #include "tombstone.h"
 #include "utility.h"
 
@@ -248,8 +248,8 @@
   return 0;
 }
 
-static bool should_attach_gdb(debugger_request_t* request) {
-  if (request->action == DEBUGGER_ACTION_CRASH) {
+static bool should_attach_gdb(const debugger_request_t& request) {
+  if (request.action == DEBUGGER_ACTION_CRASH) {
     return property_get_bool("debug.debuggerd.wait_for_gdb", false);
   }
   return false;
@@ -374,7 +374,8 @@
 }
 
 static bool perform_dump(const debugger_request_t& request, int fd, int tombstone_fd,
-                         BacktraceMap* backtrace_map, const std::set<pid_t>& siblings) {
+                         BacktraceMap* backtrace_map, const std::set<pid_t>& siblings,
+                         int* crash_signal) {
   if (TEMP_FAILURE_RETRY(write(fd, "\0", 1)) != 1) {
     ALOGE("debuggerd: failed to respond to client: %s\n", strerror(errno));
     return false;
@@ -416,11 +417,7 @@
 #endif
       case SIGTRAP:
         ALOGV("stopped -- fatal signal\n");
-        // Send a SIGSTOP to the process to make all of
-        // the non-signaled threads stop moving.  Without
-        // this we get a lot of "ptrace detach failed:
-        // No such process".
-        kill(request.pid, SIGSTOP);
+        *crash_signal = signal;
         engrave_tombstone(tombstone_fd, backtrace_map, request.pid, request.tid, siblings, signal,
                           request.original_si_code, request.abort_msg_address);
         break;
@@ -449,99 +446,7 @@
   return true;
 }
 
-// Fork a process that listens for signals to send, or 0, to exit.
-static bool fork_signal_sender(int* out_fd, pid_t* sender_pid, pid_t target_pid) {
-  int sfd[2];
-  if (socketpair(AF_UNIX, SOCK_SEQPACKET, 0, sfd) != 0) {
-    ALOGE("debuggerd: failed to create socketpair for signal sender: %s", strerror(errno));
-    return false;
-  }
-
-  pid_t fork_pid = fork();
-  if (fork_pid == -1) {
-    ALOGE("debuggerd: failed to initialize signal sender: fork failed: %s", strerror(errno));
-    return false;
-  } else if (fork_pid == 0) {
-    close(sfd[1]);
-
-    while (true) {
-      int signal;
-      int rc = TEMP_FAILURE_RETRY(read(sfd[0], &signal, sizeof(signal)));
-      if (rc < 0) {
-        ALOGE("debuggerd: signal sender failed to read from socket");
-        kill(target_pid, SIGKILL);
-        exit(1);
-      } else if (rc != sizeof(signal)) {
-        ALOGE("debuggerd: signal sender read unexpected number of bytes: %d", rc);
-        kill(target_pid, SIGKILL);
-        exit(1);
-      }
-
-      // Report success after sending a signal, or before exiting.
-      int err = 0;
-      if (signal != 0) {
-        if (kill(target_pid, signal) != 0) {
-          err = errno;
-        }
-      }
-
-      if (TEMP_FAILURE_RETRY(write(sfd[0], &err, sizeof(err))) < 0) {
-        ALOGE("debuggerd: signal sender failed to write: %s", strerror(errno));
-        kill(target_pid, SIGKILL);
-        exit(1);
-      }
-
-      if (signal == 0) {
-        exit(0);
-      }
-    }
-  } else {
-    close(sfd[0]);
-    *out_fd = sfd[1];
-    *sender_pid = fork_pid;
-    return true;
-  }
-}
-
-static void handle_request(int fd) {
-  ALOGV("handle_request(%d)\n", fd);
-
-  ScopedFd closer(fd);
-  debugger_request_t request;
-  memset(&request, 0, sizeof(request));
-  int status = read_request(fd, &request);
-  if (status != 0) {
-    return;
-  }
-
-  ALOGV("BOOM: pid=%d uid=%d gid=%d tid=%d\n", request.pid, request.uid, request.gid, request.tid);
-
-#if defined(__LP64__)
-  // On 64 bit systems, requests to dump 32 bit and 64 bit tids come
-  // to the 64 bit debuggerd. If the process is a 32 bit executable,
-  // redirect the request to the 32 bit debuggerd.
-  if (is32bit(request.tid)) {
-    // Only dump backtrace and dump tombstone requests can be redirected.
-    if (request.action == DEBUGGER_ACTION_DUMP_BACKTRACE ||
-        request.action == DEBUGGER_ACTION_DUMP_TOMBSTONE) {
-      redirect_to_32(fd, &request);
-    } else {
-      ALOGE("debuggerd: Not allowed to redirect action %d to 32 bit debuggerd\n", request.action);
-    }
-    return;
-  }
-#endif
-
-  // Fork a child to handle the rest of the request.
-  pid_t fork_pid = fork();
-  if (fork_pid == -1) {
-    ALOGE("debuggerd: failed to fork: %s\n", strerror(errno));
-    return;
-  } else if (fork_pid != 0) {
-    waitpid(fork_pid, nullptr, 0);
-    return;
-  }
-
+static void worker_process(int fd, debugger_request_t& request) {
   // Open the tombstone file if we need it.
   std::string tombstone_path;
   int tombstone_fd = -1;
@@ -582,16 +487,7 @@
 
   // Don't attach to the sibling threads if we want to attach gdb.
   // Supposedly, it makes the process less reliable.
-  bool attach_gdb = should_attach_gdb(&request);
-  int signal_fd = -1;
-  pid_t signal_pid = 0;
-
-  // Fork a process that stays root, and listens on a pipe to pause and resume the target.
-  if (!fork_signal_sender(&signal_fd, &signal_pid, request.pid)) {
-    ALOGE("debuggerd: failed to fork signal sender");
-    exit(1);
-  }
-
+  bool attach_gdb = should_attach_gdb(request);
   if (attach_gdb) {
     // Open all of the input devices we need to listen for VOLUMEDOWN before dropping privileges.
     if (init_getevent() != 0) {
@@ -601,21 +497,6 @@
 
   }
 
-  auto send_signal = [=](int signal) {
-    int error;
-    if (TEMP_FAILURE_RETRY(write(signal_fd, &signal, sizeof(signal))) < 0) {
-      ALOGE("debuggerd: failed to notify signal process: %s", strerror(errno));
-      return false;
-    } else if (TEMP_FAILURE_RETRY(read(signal_fd, &error, sizeof(error))) < 0) {
-      ALOGE("debuggerd: failed to read response from signal process: %s", strerror(errno));
-      return false;
-    } else if (error != 0) {
-      errno = error;
-      return false;
-    }
-    return true;
-  };
-
   std::set<pid_t> siblings;
   if (!attach_gdb) {
     ptrace_siblings(request.pid, request.tid, siblings);
@@ -632,7 +513,8 @@
     _exit(1);
   }
 
-  succeeded = perform_dump(request, fd, tombstone_fd, backtrace_map.get(), siblings);
+  int crash_signal = SIGKILL;
+  succeeded = perform_dump(request, fd, tombstone_fd, backtrace_map.get(), siblings, &crash_signal);
   if (succeeded) {
     if (request.action == DEBUGGER_ACTION_DUMP_TOMBSTONE) {
       if (!tombstone_path.empty()) {
@@ -643,7 +525,7 @@
 
   if (attach_gdb) {
     // Tell the signal process to send SIGSTOP to the target.
-    if (!send_signal(SIGSTOP)) {
+    if (!send_signal(request.pid, 0, SIGSTOP)) {
       ALOGE("debuggerd: failed to stop process for gdb attach: %s", strerror(errno));
       attach_gdb = false;
     }
@@ -659,9 +541,7 @@
 
   // Send the signal back to the process if it crashed and we're not waiting for gdb.
   if (!attach_gdb && request.action == DEBUGGER_ACTION_CRASH) {
-    // TODO: Send the same signal that triggered the dump, so that shell says "Segmentation fault"
-    //       instead of "Killed"?
-    if (!send_signal(SIGKILL)) {
+    if (!send_signal(request.pid, request.tid, crash_signal)) {
       ALOGE("debuggerd: failed to kill process %d: %s", request.pid, strerror(errno));
     }
   }
@@ -671,21 +551,125 @@
     wait_for_user_action(request);
 
     // Tell the signal process to send SIGCONT to the target.
-    if (!send_signal(SIGCONT)) {
+    if (!send_signal(request.pid, 0, SIGCONT)) {
       ALOGE("debuggerd: failed to resume process %d: %s", request.pid, strerror(errno));
     }
 
     uninit_getevent();
   }
 
-  if (!send_signal(0)) {
-    ALOGE("debuggerd: failed to notify signal sender to finish");
-    kill(signal_pid, SIGKILL);
-  }
-  waitpid(signal_pid, nullptr, 0);
   exit(!succeeded);
 }
 
+static void monitor_worker_process(int child_pid, const debugger_request_t& request) {
+  struct timespec timeout = {.tv_sec = 10, .tv_nsec = 0 };
+  if (should_attach_gdb(request)) {
+    // If wait_for_gdb is enabled, set the timeout to something large.
+    timeout.tv_sec = INT_MAX;
+  }
+
+  sigset_t signal_set;
+  sigemptyset(&signal_set);
+  sigaddset(&signal_set, SIGCHLD);
+
+  bool kill_worker = false;
+  bool kill_target = false;
+  bool kill_self = false;
+
+  int status;
+  siginfo_t siginfo;
+  int signal = TEMP_FAILURE_RETRY(sigtimedwait(&signal_set, &siginfo, &timeout));
+  if (signal == SIGCHLD) {
+    pid_t rc = waitpid(0, &status, WNOHANG | WUNTRACED);
+    if (rc != child_pid) {
+      ALOGE("debuggerd: waitpid returned unexpected pid (%d), committing murder-suicide", rc);
+      kill_worker = true;
+      kill_target = true;
+      kill_self = true;
+    }
+
+    if (WIFSIGNALED(status)) {
+      ALOGE("debuggerd: worker process %d terminated due to signal %d", child_pid, WTERMSIG(status));
+      kill_worker = false;
+      kill_target = true;
+    } else if (WIFSTOPPED(status)) {
+      ALOGE("debuggerd: worker process %d stopped due to signal %d", child_pid, WSTOPSIG(status));
+      kill_worker = true;
+      kill_target = true;
+    }
+  } else {
+    ALOGE("debuggerd: worker process %d timed out", child_pid);
+    kill_worker = true;
+    kill_target = true;
+  }
+
+  if (kill_worker) {
+    // Something bad happened, kill the worker.
+    if (kill(child_pid, SIGKILL) != 0) {
+      ALOGE("debuggerd: failed to kill worker process %d: %s", child_pid, strerror(errno));
+    } else {
+      waitpid(child_pid, &status, 0);
+    }
+  }
+
+  if (kill_target) {
+    // Resume or kill the target, depending on what the initial request was.
+    if (request.action == DEBUGGER_ACTION_CRASH) {
+      ALOGE("debuggerd: killing target %d", request.pid);
+      kill(request.pid, SIGKILL);
+    } else {
+      ALOGE("debuggerd: resuming target %d", request.pid);
+      kill(request.pid, SIGCONT);
+    }
+  }
+
+  if (kill_self) {
+    stop_signal_sender();
+    _exit(1);
+  }
+}
+
+static void handle_request(int fd) {
+  ALOGV("handle_request(%d)\n", fd);
+
+  ScopedFd closer(fd);
+  debugger_request_t request;
+  memset(&request, 0, sizeof(request));
+  int status = read_request(fd, &request);
+  if (status != 0) {
+    return;
+  }
+
+  ALOGW("debuggerd: handling request: pid=%d uid=%d gid=%d tid=%d\n", request.pid, request.uid,
+        request.gid, request.tid);
+
+#if defined(__LP64__)
+  // On 64 bit systems, requests to dump 32 bit and 64 bit tids come
+  // to the 64 bit debuggerd. If the process is a 32 bit executable,
+  // redirect the request to the 32 bit debuggerd.
+  if (is32bit(request.tid)) {
+    // Only dump backtrace and dump tombstone requests can be redirected.
+    if (request.action == DEBUGGER_ACTION_DUMP_BACKTRACE ||
+        request.action == DEBUGGER_ACTION_DUMP_TOMBSTONE) {
+      redirect_to_32(fd, &request);
+    } else {
+      ALOGE("debuggerd: Not allowed to redirect action %d to 32 bit debuggerd\n", request.action);
+    }
+    return;
+  }
+#endif
+
+  // Fork a child to handle the rest of the request.
+  pid_t fork_pid = fork();
+  if (fork_pid == -1) {
+    ALOGE("debuggerd: failed to fork: %s\n", strerror(errno));
+  } else if (fork_pid == 0) {
+    worker_process(fd, request);
+  } else {
+    monitor_worker_process(fork_pid, request);
+  }
+}
+
 static int do_server() {
   // debuggerd crashes can't be reported to debuggerd.
   // Reset all of the crash handlers.
@@ -702,24 +686,21 @@
   // Ignore failed writes to closed sockets
   signal(SIGPIPE, SIG_IGN);
 
-  int logsocket = socket_local_client("logd", ANDROID_SOCKET_NAMESPACE_ABSTRACT, SOCK_DGRAM);
-  if (logsocket < 0) {
-    logsocket = -1;
-  } else {
-    fcntl(logsocket, F_SETFD, FD_CLOEXEC);
-  }
+  // Block SIGCHLD so we can sigtimedwait for it.
+  sigset_t sigchld;
+  sigemptyset(&sigchld);
+  sigaddset(&sigchld, SIGCHLD);
+  sigprocmask(SIG_SETMASK, &sigchld, nullptr);
 
-  struct sigaction act;
-  act.sa_handler = SIG_DFL;
-  sigemptyset(&act.sa_mask);
-  sigaddset(&act.sa_mask,SIGCHLD);
-  act.sa_flags = SA_NOCLDWAIT;
-  sigaction(SIGCHLD, &act, 0);
+  int s = socket_local_server(SOCKET_NAME, ANDROID_SOCKET_NAMESPACE_ABSTRACT,
+                              SOCK_STREAM | SOCK_CLOEXEC);
+  if (s == -1) return 1;
 
-  int s = socket_local_server(SOCKET_NAME, ANDROID_SOCKET_NAMESPACE_ABSTRACT, SOCK_STREAM);
-  if (s < 0)
+  // Fork a process that stays root, and listens on a pipe to pause and resume the target.
+  if (!start_signal_sender()) {
+    ALOGE("debuggerd: failed to fork signal sender");
     return 1;
-  fcntl(s, F_SETFD, FD_CLOEXEC);
+  }
 
   ALOGI("debuggerd: starting\n");
 
@@ -729,14 +710,12 @@
     socklen_t alen = sizeof(ss);
 
     ALOGV("waiting for connection\n");
-    int fd = accept(s, addrp, &alen);
-    if (fd < 0) {
-      ALOGV("accept failed: %s\n", strerror(errno));
+    int fd = accept4(s, addrp, &alen, SOCK_CLOEXEC);
+    if (fd == -1) {
+      ALOGE("accept failed: %s\n", strerror(errno));
       continue;
     }
 
-    fcntl(fd, F_SETFD, FD_CLOEXEC);
-
     handle_request(fd);
   }
   return 0;
diff --git a/debuggerd/signal_sender.cpp b/debuggerd/signal_sender.cpp
new file mode 100644
index 0000000..1cfb704
--- /dev/null
+++ b/debuggerd/signal_sender.cpp
@@ -0,0 +1,152 @@
+/*
+ * Copyright (C) 2016 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#include <errno.h>
+#include <signal.h>
+#include <string.h>
+#include <sys/socket.h>
+#include <sys/syscall.h>
+#include <sys/types.h>
+#include <sys/wait.h>
+#include <unistd.h>
+
+#include <log/logger.h>
+
+#include "signal_sender.h"
+
+static int signal_fd = -1;
+static pid_t signal_pid;
+struct signal_message {
+  pid_t pid;
+  pid_t tid;
+  int signal;
+};
+
+// Fork a process to send signals for the worker processes to use after they've dropped privileges.
+bool start_signal_sender() {
+  if (signal_pid != 0) {
+    ALOGE("debuggerd: attempted to start signal sender multiple times");
+    return false;
+  }
+
+  int sfd[2];
+  if (socketpair(AF_UNIX, SOCK_SEQPACKET | SOCK_CLOEXEC, 0, sfd) != 0) {
+    ALOGE("debuggerd: failed to create socketpair for signal sender: %s", strerror(errno));
+    return false;
+  }
+
+  pid_t parent = getpid();
+  pid_t fork_pid = fork();
+  if (fork_pid == -1) {
+    ALOGE("debuggerd: failed to initialize signal sender: fork failed: %s", strerror(errno));
+    return false;
+  } else if (fork_pid == 0) {
+    close(sfd[1]);
+
+    while (true) {
+      signal_message msg;
+      int rc = TEMP_FAILURE_RETRY(read(sfd[0], &msg, sizeof(msg)));
+      if (rc < 0) {
+        ALOGE("debuggerd: signal sender failed to read from socket");
+        break;
+      } else if (rc != sizeof(msg)) {
+        ALOGE("debuggerd: signal sender read unexpected number of bytes: %d", rc);
+        break;
+      }
+
+      // Report success after sending a signal
+      int err = 0;
+      if (msg.tid > 0) {
+        if (syscall(SYS_tgkill, msg.pid, msg.tid, msg.signal) != 0) {
+          err = errno;
+        }
+      } else {
+        if (kill(msg.pid, msg.signal) != 0) {
+          err = errno;
+        }
+      }
+
+      if (TEMP_FAILURE_RETRY(write(sfd[0], &err, sizeof(err))) < 0) {
+        ALOGE("debuggerd: signal sender failed to write: %s", strerror(errno));
+      }
+    }
+
+    // Our parent proably died, but if not, kill them.
+    if (getppid() == parent) {
+      kill(parent, SIGKILL);
+    }
+    _exit(1);
+  } else {
+    close(sfd[0]);
+    signal_fd = sfd[1];
+    signal_pid = fork_pid;
+    return true;
+  }
+}
+
+bool stop_signal_sender() {
+  if (signal_pid <= 0) {
+    return false;
+  }
+
+  if (kill(signal_pid, SIGKILL) != 0) {
+    ALOGE("debuggerd: failed to kill signal sender: %s", strerror(errno));
+    return false;
+  }
+
+  close(signal_fd);
+  signal_fd = -1;
+
+  int status;
+  waitpid(signal_pid, &status, 0);
+  signal_pid = 0;
+
+  return true;
+}
+
+bool send_signal(pid_t pid, pid_t tid, int signal) {
+  if (signal_fd == -1) {
+    ALOGE("debuggerd: attempted to send signal before signal sender was started");
+    errno = EHOSTUNREACH;
+    return false;
+  }
+
+  signal_message msg = {.pid = pid, .tid = tid, .signal = signal };
+  if (TEMP_FAILURE_RETRY(write(signal_fd, &msg, sizeof(msg))) < 0) {
+    ALOGE("debuggerd: failed to send message to signal sender: %s", strerror(errno));
+    errno = EHOSTUNREACH;
+    return false;
+  }
+
+  int response;
+  ssize_t rc = TEMP_FAILURE_RETRY(read(signal_fd, &response, sizeof(response)));
+  if (rc == 0) {
+    ALOGE("debuggerd: received EOF from signal sender");
+    errno = EHOSTUNREACH;
+    return false;
+  } else if (rc < 0) {
+    ALOGE("debuggerd: failed to receive response from signal sender: %s", strerror(errno));
+    errno = EHOSTUNREACH;
+    return false;
+  }
+
+  if (response == 0) {
+    return true;
+  }
+
+  errno = response;
+  return false;
+}
diff --git a/debuggerd/signal_sender.h b/debuggerd/signal_sender.h
new file mode 100644
index 0000000..0443272
--- /dev/null
+++ b/debuggerd/signal_sender.h
@@ -0,0 +1,30 @@
+/*
+ * Copyright (C) 2016 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#ifndef _DEBUGGERD_SIGNAL_SENDER_H
+#define _DEBUGGERD_SIGNAL_SENDER_H
+
+#include <sys/types.h>
+
+bool start_signal_sender();
+bool stop_signal_sender();
+
+// Sends a signal to a target process or thread.
+// If tid is greater than zero, this performs tgkill(pid, tid, signal).
+// Otherwise, it performs kill(pid, signal).
+bool send_signal(pid_t pid, pid_t tid, int signal);
+
+#endif
diff --git a/liblog/tests/liblog_test.cpp b/liblog/tests/liblog_test.cpp
index ecd3b04..af3a3b4 100644
--- a/liblog/tests/liblog_test.cpp
+++ b/liblog/tests/liblog_test.cpp
@@ -16,6 +16,7 @@
 
 #include <fcntl.h>
 #include <inttypes.h>
+#include <semaphore.h>
 #include <signal.h>
 #include <string.h>
 #include <sys/types.h>
@@ -470,9 +471,15 @@
 }
 
 static unsigned signaled;
-log_time signal_time;
+static log_time signal_time;
 
-static void caught_blocking(int /*signum*/)
+/*
+ *  Strictly, we are not allowed to log messages in a signal context, but we
+ * do make an effort to keep the failure surface minimized, and this in-effect
+ * should catch any regressions in that effort. The odds of a logged message
+ * in a signal handler causing a lockup problem should be _very_ small.
+ */
+static void caught_blocking_signal(int /*signum*/)
 {
     unsigned long long v = 0xDEADBEEFA55A0000ULL;
 
@@ -522,7 +529,7 @@
     }
 }
 
-TEST(liblog, android_logger_list_read__cpu) {
+TEST(liblog, android_logger_list_read__cpu_signal) {
     struct logger_list *logger_list;
     unsigned long long v = 0xDEADBEEFA55A0000ULL;
 
@@ -545,7 +552,7 @@
 
     memset(&signal_time, 0, sizeof(signal_time));
 
-    signal(SIGALRM, caught_blocking);
+    signal(SIGALRM, caught_blocking_signal);
     alarm(alarm_time);
 
     signaled = 0;
@@ -590,7 +597,158 @@
     alarm(0);
     signal(SIGALRM, SIG_DFL);
 
-    EXPECT_LT(1, count);
+    EXPECT_LE(1, count);
+
+    EXPECT_EQ(1, signals);
+
+    android_logger_list_close(logger_list);
+
+    unsigned long long uticks_end;
+    unsigned long long sticks_end;
+    get_ticks(&uticks_end, &sticks_end);
+
+    // Less than 1% in either user or system time, or both
+    const unsigned long long one_percent_ticks = alarm_time;
+    unsigned long long user_ticks = uticks_end - uticks_start;
+    unsigned long long system_ticks = sticks_end - sticks_start;
+    EXPECT_GT(one_percent_ticks, user_ticks);
+    EXPECT_GT(one_percent_ticks, system_ticks);
+    EXPECT_GT(one_percent_ticks, user_ticks + system_ticks);
+}
+
+/*
+ *  Strictly, we are not allowed to log messages in a signal context, the
+ * correct way to handle this is to ensure the messages are constructed in
+ * a thread; the signal handler should only unblock the thread.
+ */
+static sem_t thread_trigger;
+
+static void caught_blocking_thread(int /*signum*/)
+{
+    sem_post(&thread_trigger);
+}
+
+static void *running_thread(void *) {
+    unsigned long long v = 0xDEADBEAFA55A0000ULL;
+
+    v += getpid() & 0xFFFF;
+
+    struct timespec timeout;
+    clock_gettime(CLOCK_REALTIME, &timeout);
+    timeout.tv_sec += 55;
+    sem_timedwait(&thread_trigger, &timeout);
+
+    ++signaled;
+    if ((signal_time.tv_sec == 0) && (signal_time.tv_nsec == 0)) {
+        signal_time = log_time(CLOCK_MONOTONIC);
+        signal_time.tv_sec += 2;
+    }
+
+    LOG_FAILURE_RETRY(__android_log_btwrite(0, EVENT_TYPE_LONG, &v, sizeof(v)));
+
+    return NULL;
+}
+
+int start_thread()
+{
+    sem_init(&thread_trigger, 0, 0);
+
+    pthread_attr_t attr;
+    if (pthread_attr_init(&attr)) {
+        return -1;
+    }
+
+    struct sched_param param;
+
+    memset(&param, 0, sizeof(param));
+    pthread_attr_setschedparam(&attr, &param);
+    pthread_attr_setschedpolicy(&attr, SCHED_BATCH);
+
+    if (pthread_attr_setdetachstate(&attr, PTHREAD_CREATE_DETACHED)) {
+        pthread_attr_destroy(&attr);
+        return -1;
+    }
+
+    pthread_t thread;
+    if (pthread_create(&thread, &attr, running_thread, NULL)) {
+        pthread_attr_destroy(&attr);
+        return -1;
+    }
+
+    pthread_attr_destroy(&attr);
+    return 0;
+}
+
+TEST(liblog, android_logger_list_read__cpu_thread) {
+    struct logger_list *logger_list;
+    unsigned long long v = 0xDEADBEAFA55A0000ULL;
+
+    pid_t pid = getpid();
+
+    v += pid & 0xFFFF;
+
+    ASSERT_TRUE(NULL != (logger_list = android_logger_list_open(
+        LOG_ID_EVENTS, ANDROID_LOG_RDONLY, 1000, pid)));
+
+    int count = 0;
+
+    int signals = 0;
+
+    unsigned long long uticks_start;
+    unsigned long long sticks_start;
+    get_ticks(&uticks_start, &sticks_start);
+
+    const unsigned alarm_time = 10;
+
+    memset(&signal_time, 0, sizeof(signal_time));
+
+    signaled = 0;
+    EXPECT_EQ(0, start_thread());
+
+    signal(SIGALRM, caught_blocking_thread);
+    alarm(alarm_time);
+
+    do {
+        log_msg log_msg;
+        if (LOG_FAILURE_RETRY(android_logger_list_read(logger_list, &log_msg)) <= 0) {
+            break;
+        }
+
+        alarm(alarm_time);
+
+        ++count;
+
+        ASSERT_EQ(log_msg.entry.pid, pid);
+
+        if ((log_msg.entry.len != (4 + 1 + 8))
+         || (log_msg.id() != LOG_ID_EVENTS)) {
+            continue;
+        }
+
+        char *eventData = log_msg.msg();
+
+        if (eventData[4] != EVENT_TYPE_LONG) {
+            continue;
+        }
+
+        unsigned long long l = eventData[4 + 1 + 0] & 0xFF;
+        l |= (unsigned long long) (eventData[4 + 1 + 1] & 0xFF) << 8;
+        l |= (unsigned long long) (eventData[4 + 1 + 2] & 0xFF) << 16;
+        l |= (unsigned long long) (eventData[4 + 1 + 3] & 0xFF) << 24;
+        l |= (unsigned long long) (eventData[4 + 1 + 4] & 0xFF) << 32;
+        l |= (unsigned long long) (eventData[4 + 1 + 5] & 0xFF) << 40;
+        l |= (unsigned long long) (eventData[4 + 1 + 6] & 0xFF) << 48;
+        l |= (unsigned long long) (eventData[4 + 1 + 7] & 0xFF) << 56;
+
+        if (l == v) {
+            ++signals;
+            break;
+        }
+    } while (!signaled || (log_time(CLOCK_MONOTONIC) < signal_time));
+    alarm(0);
+    signal(SIGALRM, SIG_DFL);
+
+    EXPECT_LE(1, count);
 
     EXPECT_EQ(1, signals);
 
@@ -971,11 +1129,20 @@
         struct logger * logger;
         EXPECT_TRUE(NULL != (logger = android_logger_open(logger_list, id)));
         EXPECT_EQ(id, android_logger_get_id(logger));
-        EXPECT_LT(0, android_logger_get_log_size(logger));
-        /* crash buffer is allowed to be empty, that is actually healthy! */
-        if (android_logger_get_log_readable_size(logger) ||
-                (strcmp("crash", name) && strcmp("security", name))) {
-            EXPECT_LT(0, android_logger_get_log_readable_size(logger));
+        ssize_t get_log_size = android_logger_get_log_size(logger);
+        /* security buffer is allowed to be denied */
+        if (strcmp("security", name)) {
+            EXPECT_LT(0, get_log_size);
+            /* crash buffer is allowed to be empty, that is actually healthy! */
+            EXPECT_LE((strcmp("crash", name)) != 0,
+                      android_logger_get_log_readable_size(logger));
+        } else {
+            EXPECT_NE(0, get_log_size);
+            if (get_log_size < 0) {
+                EXPECT_GT(0, android_logger_get_log_readable_size(logger));
+            } else {
+                EXPECT_LE(0, android_logger_get_log_readable_size(logger));
+            }
         }
         EXPECT_LT(0, android_logger_get_log_version(logger));
     }
diff --git a/libnativeloader/include/nativeloader/native_loader.h b/libnativeloader/include/nativeloader/native_loader.h
index b16c0e6..1bd3b8f 100644
--- a/libnativeloader/include/nativeloader/native_loader.h
+++ b/libnativeloader/include/nativeloader/native_loader.h
@@ -26,7 +26,7 @@
 namespace android {
 
 __attribute__((visibility("default")))
-void PreloadPublicNativeLibraries();
+void InitializeNativeLoader();
 
 __attribute__((visibility("default")))
 jstring CreateClassLoaderNamespace(JNIEnv* env,
diff --git a/libnativeloader/native_loader.cpp b/libnativeloader/native_loader.cpp
index 3e4b15a..e6b37ed 100644
--- a/libnativeloader/native_loader.cpp
+++ b/libnativeloader/native_loader.cpp
@@ -29,34 +29,14 @@
 #include <string>
 #include <mutex>
 
+#include "android-base/file.h"
 #include "android-base/macros.h"
 #include "android-base/strings.h"
 
 namespace android {
 
-#ifdef __ANDROID__
-// TODO(dimitry): move this to system properties.
-static const char* kPublicNativeLibraries = "libandroid.so:"
-                                            "libc.so:"
-                                            "libcamera2ndk.so:"
-                                            "libdl.so:"
-                                            "libEGL.so:"
-                                            "libGLESv1_CM.so:"
-                                            "libGLESv2.so:"
-                                            "libGLESv3.so:"
-                                            "libicui18n.so:"
-                                            "libicuuc.so:"
-                                            "libjnigraphics.so:"
-                                            "liblog.so:"
-                                            "libmediandk.so:"
-                                            "libm.so:"
-                                            "libOpenMAXAL.so:"
-                                            "libOpenSLES.so:"
-                                            "libRS.so:"
-                                            "libstdc++.so:"
-                                            "libvulkan.so:"
-                                            "libwebviewchromium_plat_support.so:"
-                                            "libz.so";
+#if defined(__ANDROID__)
+static constexpr const char* kPublicNativeLibrariesConfig = "/system/etc/public.libraries.txt";
 
 class LibraryNamespaces {
  public:
@@ -82,7 +62,8 @@
 
     android_namespace_t* ns = FindNamespaceByClassLoader(env, class_loader);
 
-    LOG_FATAL_IF(ns != nullptr, "There is already a namespace associated with this classloader");
+    LOG_ALWAYS_FATAL_IF(ns != nullptr,
+                        "There is already a namespace associated with this classloader");
 
     uint64_t namespace_type = ANDROID_NAMESPACE_TYPE_ISOLATED;
     if (is_shared) {
@@ -112,10 +93,30 @@
     return it != namespaces_.end() ? it->second : nullptr;
   }
 
-  void PreloadPublicLibraries() {
+  void Initialize() {
+    // Read list of public native libraries from the config file.
+    std::string file_content;
+    LOG_ALWAYS_FATAL_IF(!base::ReadFileToString(kPublicNativeLibrariesConfig, &file_content),
+                        "Error reading public native library list from \"%s\": %s",
+                        kPublicNativeLibrariesConfig, strerror(errno));
+
+    std::vector<std::string> lines = base::Split(file_content, "\n");
+
+    std::vector<std::string> sonames;
+
+    for (const auto& line : lines) {
+      auto trimmed_line = base::Trim(line);
+      if (trimmed_line[0] == '#' || trimmed_line.empty()) {
+        continue;
+      }
+
+      sonames.push_back(trimmed_line);
+    }
+
+    public_libraries_ = base::Join(sonames, ':');
+
     // android_init_namespaces() expects all the public libraries
     // to be loaded so that they can be found by soname alone.
-    std::vector<std::string> sonames = android::base::Split(kPublicNativeLibraries, ":");
     for (const auto& soname : sonames) {
       dlopen(soname.c_str(), RTLD_NOW | RTLD_NODELETE);
     }
@@ -123,9 +124,7 @@
 
  private:
   bool InitPublicNamespace(const char* library_path, int32_t target_sdk_version) {
-    // Some apps call dlopen from generated code unknown to linker in which
-    // case linker uses anonymous namespace. See b/25844435 for details.
-    std::string publicNativeLibraries = kPublicNativeLibraries;
+    std::string publicNativeLibraries = public_libraries_;
 
     // TODO (dimitry): This is a workaround for http://b/26436837
     // will be removed before the release.
@@ -139,6 +138,10 @@
     }
     // END OF WORKAROUND
 
+    // (http://b/25844435) - Some apps call dlopen from generated code (mono jited
+    // code is one example) unknown to linker in which  case linker uses anonymous
+    // namespace. The second argument specifies the search path for the anonymous
+    // namespace which is the library_path of the classloader.
     initialized_ = android_init_namespaces(publicNativeLibraries.c_str(), library_path);
 
     return initialized_;
@@ -146,6 +149,8 @@
 
   bool initialized_;
   std::vector<std::pair<jweak, android_namespace_t*>> namespaces_;
+  std::string public_libraries_;
+
 
   DISALLOW_COPY_AND_ASSIGN(LibraryNamespaces);
 };
@@ -158,10 +163,10 @@
 }
 #endif
 
-void PreloadPublicNativeLibraries() {
+void InitializeNativeLoader() {
 #if defined(__ANDROID__)
   std::lock_guard<std::mutex> guard(g_namespaces_mutex);
-  g_namespaces->PreloadPublicLibraries();
+  g_namespaces->Initialize();
 #endif
 }
 
diff --git a/rootdir/etc/public.libraries.android.txt b/rootdir/etc/public.libraries.android.txt
new file mode 100644
index 0000000..6244761
--- /dev/null
+++ b/rootdir/etc/public.libraries.android.txt
@@ -0,0 +1,20 @@
+libandroid.so
+libc.so
+libdl.so
+libEGL.so
+libGLESv1_CM.so
+libGLESv2.so
+libGLESv3.so
+libicui18n.so
+libicuuc.so
+libjnigraphics.so
+liblog.so
+libmediandk.so
+libm.so
+libOpenMAXAL.so
+libOpenSLES.so
+libRS.so
+libstdc++.so
+libvulkan.so
+libwebviewchromium_plat_support.so
+libz.so
diff --git a/rootdir/etc/public.libraries.wear.txt b/rootdir/etc/public.libraries.wear.txt
new file mode 100644
index 0000000..d499f38
--- /dev/null
+++ b/rootdir/etc/public.libraries.wear.txt
@@ -0,0 +1,19 @@
+libandroid.so
+libc.so
+libdl.so
+libEGL.so
+libGLESv1_CM.so
+libGLESv2.so
+libGLESv3.so
+libicui18n.so
+libicuuc.so
+libjnigraphics.so
+liblog.so
+libmediandk.so
+libm.so
+libOpenMAXAL.so
+libOpenSLES.so
+libRS.so
+libstdc++.so
+libvulkan.so
+libz.so
diff --git a/rootdir/init.rc b/rootdir/init.rc
index 194b41b..a95eaa2 100644
--- a/rootdir/init.rc
+++ b/rootdir/init.rc
@@ -62,6 +62,10 @@
     mount tmpfs tmpfs /mnt mode=0755,uid=0,gid=1000
     restorecon_recursive /mnt
 
+    mount configfs none /config
+    chmod 0775 /config/sdcardfs
+    chown system package_info /config/sdcardfs
+
     mkdir /mnt/secure 0700 root root
     mkdir /mnt/secure/asec 0700 root root
     mkdir /mnt/asec 0755 root system
diff --git a/sdcard/sdcard.c b/sdcard/sdcard.c
index 45efe36..d8fda67 100644
--- a/sdcard/sdcard.c
+++ b/sdcard/sdcard.c
@@ -1894,6 +1894,105 @@
     exit(1);
 }
 
+static int sdcardfs_setup(const char *source_path, const char *dest_path, uid_t fsuid,
+                        gid_t fsgid, bool multi_user, userid_t userid, gid_t gid, mode_t mask) {
+    char opts[256];
+
+    snprintf(opts, sizeof(opts),
+            "fsuid=%d,fsgid=%d,%smask=%d,userid=%d,gid=%d",
+            fsuid, fsgid, multi_user?"multiuser,":"", mask, userid, gid);
+
+    if (mount(source_path, dest_path, "sdcardfs",
+                        MS_NOSUID | MS_NODEV | MS_NOEXEC | MS_NOATIME, opts) != 0) {
+        ERROR("failed to mount sdcardfs filesystem: %s\n", strerror(errno));
+        return -1;
+    }
+
+    return 0;
+}
+
+static void run_sdcardfs(const char* source_path, const char* label, uid_t uid,
+        gid_t gid, userid_t userid, bool multi_user, bool full_write) {
+    char dest_path_default[PATH_MAX];
+    char dest_path_read[PATH_MAX];
+    char dest_path_write[PATH_MAX];
+    char obb_path[PATH_MAX];
+    snprintf(dest_path_default, PATH_MAX, "/mnt/runtime/default/%s", label);
+    snprintf(dest_path_read, PATH_MAX, "/mnt/runtime/read/%s", label);
+    snprintf(dest_path_write, PATH_MAX, "/mnt/runtime/write/%s", label);
+
+    umask(0);
+    if (multi_user) {
+        /* Multi-user storage is fully isolated per user, so "other"
+         * permissions are completely masked off. */
+        if (sdcardfs_setup(source_path, dest_path_default, uid, gid, multi_user, userid,
+                                                      AID_SDCARD_RW, 0006)
+                || sdcardfs_setup(source_path, dest_path_read, uid, gid, multi_user, userid,
+                                                      AID_EVERYBODY, 0027)
+                || sdcardfs_setup(source_path, dest_path_write, uid, gid, multi_user, userid,
+                                                      AID_EVERYBODY, full_write ? 0007 : 0027)) {
+            ERROR("failed to fuse_setup\n");
+            exit(1);
+        }
+    } else {
+        /* Physical storage is readable by all users on device, but
+         * the Android directories are masked off to a single user
+         * deep inside attr_from_stat(). */
+        if (sdcardfs_setup(source_path, dest_path_default, uid, gid, multi_user, userid,
+                                                      AID_SDCARD_RW, 0006)
+                || sdcardfs_setup(source_path, dest_path_read, uid, gid, multi_user, userid,
+                                                      AID_EVERYBODY, full_write ? 0027 : 0022)
+                || sdcardfs_setup(source_path, dest_path_write, uid, gid, multi_user, userid,
+                                                      AID_EVERYBODY, full_write ? 0007 : 0022)) {
+            ERROR("failed to fuse_setup\n");
+            exit(1);
+        }
+    }
+
+    /* Drop privs */
+    if (setgroups(sizeof(kGroups) / sizeof(kGroups[0]), kGroups) < 0) {
+        ERROR("cannot setgroups: %s\n", strerror(errno));
+        exit(1);
+    }
+    if (setgid(gid) < 0) {
+        ERROR("cannot setgid: %s\n", strerror(errno));
+        exit(1);
+    }
+    if (setuid(uid) < 0) {
+        ERROR("cannot setuid: %s\n", strerror(errno));
+        exit(1);
+    }
+
+    if (multi_user) {
+        snprintf(obb_path, sizeof(obb_path), "%s/obb", source_path);
+        fs_prepare_dir(&obb_path[0], 0775, uid, gid);
+    }
+
+    exit(0);
+}
+
+static bool supports_sdcardfs(void) {
+    FILE *fp;
+    char *buf = NULL;
+    size_t buflen = 0;
+
+    fp = fopen("/proc/filesystems", "r");
+    if (!fp) {
+        ERROR("Could not read /proc/filesystems, error: %s\n", strerror(errno));
+        return false;
+    }
+    while ((getline(&buf, &buflen, fp)) > 0) {
+        if (strstr(buf, "sdcardfs\n")) {
+            free(buf);
+            fclose(fp);
+            return true;
+        }
+    }
+    free(buf);
+    fclose(fp);
+    return false;
+}
+
 int main(int argc, char **argv) {
     const char *source_path = NULL;
     const char *label = NULL;
@@ -1966,6 +2065,10 @@
         sleep(1);
     }
 
-    run(source_path, label, uid, gid, userid, multi_user, full_write);
+    if (supports_sdcardfs()) {
+        run_sdcardfs(source_path, label, uid, gid, userid, multi_user, full_write);
+    } else {
+        run(source_path, label, uid, gid, userid, multi_user, full_write);
+    }
     return 1;
 }