Jeff Sharkey | 3d1cb6a | 2016-02-27 21:10:34 -0700 | [diff] [blame] | 1 | /* |
| 2 | * Copyright (C) 2016 The Android Open Source Project |
| 3 | * |
| 4 | * Licensed under the Apache License, Version 2.0 (the "License"); |
| 5 | * you may not use this file except in compliance with the License. |
| 6 | * You may obtain a copy of the License at |
| 7 | * |
| 8 | * http://www.apache.org/licenses/LICENSE-2.0 |
| 9 | * |
| 10 | * Unless required by applicable law or agreed to in writing, software |
| 11 | * distributed under the License is distributed on an "AS IS" BASIS, |
| 12 | * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. |
| 13 | * See the License for the specific language governing permissions and |
| 14 | * limitations under the License. |
| 15 | */ |
| 16 | |
| 17 | package com.android.server; |
| 18 | |
Makoto Onuki | eed5b5a | 2018-03-13 14:22:23 -0700 | [diff] [blame] | 19 | import android.annotation.Nullable; |
| 20 | import android.text.TextUtils; |
Jeff Sharkey | 3d1cb6a | 2016-02-27 21:10:34 -0700 | [diff] [blame] | 21 | import android.util.ArrayMap; |
| 22 | import android.util.ArraySet; |
| 23 | import android.util.Slog; |
| 24 | |
Makoto Onuki | eed5b5a | 2018-03-13 14:22:23 -0700 | [diff] [blame] | 25 | import com.android.internal.os.BackgroundThread; |
| 26 | |
Jeff Sharkey | 3d1cb6a | 2016-02-27 21:10:34 -0700 | [diff] [blame] | 27 | import java.io.FileDescriptor; |
| 28 | import java.io.PrintWriter; |
| 29 | |
| 30 | /** |
| 31 | * LockGuard is a mechanism to help detect lock inversions inside the system |
| 32 | * server. It works by requiring each lock acquisition site to follow this |
| 33 | * pattern: |
| 34 | * |
| 35 | * <pre> |
| 36 | * synchronized (LockGuard.guard(lock)) { |
| 37 | * } |
| 38 | * </pre> |
| 39 | * |
| 40 | * <pre> |
| 41 | * $ find services/ -name "*.java" -exec sed -i -r \ |
| 42 | * 's/synchronized.?\((.+?)\)/synchronized \(com.android.server.LockGuard.guard\(\1\)\)/' {} \; |
| 43 | * </pre> |
| 44 | * |
| 45 | * The {@link #guard(Object)} method internally verifies that all locking is |
| 46 | * done in a consistent order, and will log if any inversion is detected. For |
| 47 | * example, if the calling thread is trying to acquire the |
| 48 | * {@code ActivityManager} lock while holding the {@code PackageManager} lock, |
| 49 | * it will yell. |
| 50 | * <p> |
| 51 | * This class requires no prior knowledge of locks or their ordering; it derives |
| 52 | * all of this data at runtime. However, this means the overhead is |
| 53 | * <em>substantial</em> and it should not be enabled by default. For example, |
| 54 | * here are some benchmarked timings: |
| 55 | * <ul> |
| 56 | * <li>An unguarded synchronized block takes 40ns. |
| 57 | * <li>A guarded synchronized block takes 50ns when disabled. |
| 58 | * <li>A guarded synchronized block takes 460ns per lock checked when enabled. |
| 59 | * </ul> |
Jeff Sharkey | 5f3e934 | 2017-03-13 14:53:11 -0600 | [diff] [blame] | 60 | * <p> |
| 61 | * This class also supports a second simpler mode of operation where well-known |
| 62 | * locks are explicitly registered and checked via indexes. |
Jeff Sharkey | 3d1cb6a | 2016-02-27 21:10:34 -0700 | [diff] [blame] | 63 | */ |
| 64 | public class LockGuard { |
| 65 | private static final String TAG = "LockGuard"; |
| 66 | |
Jeff Sharkey | 5f3e934 | 2017-03-13 14:53:11 -0600 | [diff] [blame] | 67 | /** |
| 68 | * Well-known locks ordered by fixed index. Locks with a specific index |
| 69 | * should never be acquired while holding a lock of a lower index. |
| 70 | */ |
| 71 | public static final int INDEX_APP_OPS = 0; |
| 72 | public static final int INDEX_POWER = 1; |
| 73 | public static final int INDEX_USER = 2; |
| 74 | public static final int INDEX_PACKAGES = 3; |
| 75 | public static final int INDEX_STORAGE = 4; |
| 76 | public static final int INDEX_WINDOW = 5; |
| 77 | public static final int INDEX_ACTIVITY = 6; |
Makoto Onuki | eed5b5a | 2018-03-13 14:22:23 -0700 | [diff] [blame] | 78 | public static final int INDEX_DPMS = 7; |
Jeff Sharkey | 5f3e934 | 2017-03-13 14:53:11 -0600 | [diff] [blame] | 79 | |
Makoto Onuki | eed5b5a | 2018-03-13 14:22:23 -0700 | [diff] [blame] | 80 | private static Object[] sKnownFixed = new Object[INDEX_DPMS + 1]; |
Jeff Sharkey | 5f3e934 | 2017-03-13 14:53:11 -0600 | [diff] [blame] | 81 | |
Jeff Sharkey | 3d1cb6a | 2016-02-27 21:10:34 -0700 | [diff] [blame] | 82 | private static ArrayMap<Object, LockInfo> sKnown = new ArrayMap<>(0, true); |
| 83 | |
| 84 | private static class LockInfo { |
| 85 | /** Friendly label to describe this lock */ |
| 86 | public String label; |
| 87 | |
| 88 | /** Child locks that can be acquired while this lock is already held */ |
| 89 | public ArraySet<Object> children = new ArraySet<>(0, true); |
Makoto Onuki | eed5b5a | 2018-03-13 14:22:23 -0700 | [diff] [blame] | 90 | |
| 91 | /** If true, do wtf instead of a warning log. */ |
| 92 | public boolean doWtf; |
Jeff Sharkey | 3d1cb6a | 2016-02-27 21:10:34 -0700 | [diff] [blame] | 93 | } |
| 94 | |
| 95 | private static LockInfo findOrCreateLockInfo(Object lock) { |
| 96 | LockInfo info = sKnown.get(lock); |
| 97 | if (info == null) { |
| 98 | info = new LockInfo(); |
| 99 | info.label = "0x" + Integer.toHexString(System.identityHashCode(lock)) + " [" |
| 100 | + new Throwable().getStackTrace()[2].toString() + "]"; |
| 101 | sKnown.put(lock, info); |
| 102 | } |
| 103 | return info; |
| 104 | } |
| 105 | |
| 106 | /** |
| 107 | * Check if the calling thread is holding any locks in an inverted order. |
| 108 | * |
| 109 | * @param lock The lock the calling thread is attempting to acquire. |
| 110 | */ |
| 111 | public static Object guard(Object lock) { |
| 112 | // If we already hold this lock, ignore |
| 113 | if (lock == null || Thread.holdsLock(lock)) return lock; |
| 114 | |
| 115 | // Check to see if we're already holding any child locks |
| 116 | boolean triggered = false; |
| 117 | final LockInfo info = findOrCreateLockInfo(lock); |
| 118 | for (int i = 0; i < info.children.size(); i++) { |
| 119 | final Object child = info.children.valueAt(i); |
| 120 | if (child == null) continue; |
| 121 | |
| 122 | if (Thread.holdsLock(child)) { |
Makoto Onuki | eed5b5a | 2018-03-13 14:22:23 -0700 | [diff] [blame] | 123 | doLog(lock, "Calling thread " + Thread.currentThread().getName() |
| 124 | + " is holding " + lockToString(child) + " while trying to acquire " |
| 125 | + lockToString(lock)); |
Jeff Sharkey | 3d1cb6a | 2016-02-27 21:10:34 -0700 | [diff] [blame] | 126 | triggered = true; |
| 127 | } |
| 128 | } |
| 129 | |
| 130 | if (!triggered) { |
| 131 | // If no trouble found above, record this lock as being a valid |
| 132 | // child of all locks currently being held |
| 133 | for (int i = 0; i < sKnown.size(); i++) { |
| 134 | final Object test = sKnown.keyAt(i); |
| 135 | if (test == null || test == lock) continue; |
| 136 | |
| 137 | if (Thread.holdsLock(test)) { |
| 138 | sKnown.valueAt(i).children.add(lock); |
| 139 | } |
| 140 | } |
| 141 | } |
| 142 | |
| 143 | return lock; |
| 144 | } |
| 145 | |
| 146 | /** |
Jeff Sharkey | 5f3e934 | 2017-03-13 14:53:11 -0600 | [diff] [blame] | 147 | * Yell if any lower-level locks are being held by the calling thread that |
| 148 | * is about to acquire the given lock. |
| 149 | */ |
| 150 | public static void guard(int index) { |
| 151 | for (int i = 0; i < index; i++) { |
| 152 | final Object lock = sKnownFixed[i]; |
| 153 | if (lock != null && Thread.holdsLock(lock)) { |
Makoto Onuki | eed5b5a | 2018-03-13 14:22:23 -0700 | [diff] [blame] | 154 | |
| 155 | // Note in this case sKnownFixed may not contain a lock at the given index, |
| 156 | // which is okay and in that case we just don't do a WTF. |
| 157 | final Object targetMayBeNull = sKnownFixed[index]; |
| 158 | doLog(targetMayBeNull, "Calling thread " + Thread.currentThread().getName() |
| 159 | + " is holding " + lockToString(i) + " while trying to acquire " |
| 160 | + lockToString(index)); |
Jeff Sharkey | 5f3e934 | 2017-03-13 14:53:11 -0600 | [diff] [blame] | 161 | } |
| 162 | } |
| 163 | } |
| 164 | |
Makoto Onuki | eed5b5a | 2018-03-13 14:22:23 -0700 | [diff] [blame] | 165 | private static void doLog(@Nullable Object lock, String message) { |
| 166 | if (lock != null && findOrCreateLockInfo(lock).doWtf) { |
| 167 | |
| 168 | // Don't want to call into ActivityManager with any lock held, so let's just call it |
| 169 | // from a new thread. We don't want to use known threads (e.g. BackgroundThread) either |
| 170 | // because they may be stuck too. |
| 171 | final Throwable stackTrace = new RuntimeException(message); |
| 172 | new Thread(() -> Slog.wtf(TAG, stackTrace)).start(); |
| 173 | return; |
| 174 | } |
| 175 | Slog.w(TAG, message, new Throwable()); |
| 176 | } |
| 177 | |
Jeff Sharkey | 5f3e934 | 2017-03-13 14:53:11 -0600 | [diff] [blame] | 178 | /** |
Jeff Sharkey | 3d1cb6a | 2016-02-27 21:10:34 -0700 | [diff] [blame] | 179 | * Report the given lock with a well-known label. |
| 180 | */ |
Jeff Sharkey | 5f3e934 | 2017-03-13 14:53:11 -0600 | [diff] [blame] | 181 | public static Object installLock(Object lock, String label) { |
Jeff Sharkey | 3d1cb6a | 2016-02-27 21:10:34 -0700 | [diff] [blame] | 182 | final LockInfo info = findOrCreateLockInfo(lock); |
| 183 | info.label = label; |
Jeff Sharkey | 5f3e934 | 2017-03-13 14:53:11 -0600 | [diff] [blame] | 184 | return lock; |
| 185 | } |
| 186 | |
| 187 | /** |
| 188 | * Report the given lock with a well-known index. |
| 189 | */ |
| 190 | public static Object installLock(Object lock, int index) { |
Makoto Onuki | eed5b5a | 2018-03-13 14:22:23 -0700 | [diff] [blame] | 191 | return installLock(lock, index, /*doWtf=*/ false); |
| 192 | } |
| 193 | |
| 194 | /** |
| 195 | * Report the given lock with a well-known index. |
| 196 | */ |
| 197 | public static Object installLock(Object lock, int index, boolean doWtf) { |
Jeff Sharkey | 5f3e934 | 2017-03-13 14:53:11 -0600 | [diff] [blame] | 198 | sKnownFixed[index] = lock; |
Makoto Onuki | eed5b5a | 2018-03-13 14:22:23 -0700 | [diff] [blame] | 199 | final LockInfo info = findOrCreateLockInfo(lock); |
| 200 | info.doWtf = doWtf; |
| 201 | info.label = "Lock-" + lockToString(index); |
Jeff Sharkey | 5f3e934 | 2017-03-13 14:53:11 -0600 | [diff] [blame] | 202 | return lock; |
| 203 | } |
| 204 | |
| 205 | public static Object installNewLock(int index) { |
Makoto Onuki | eed5b5a | 2018-03-13 14:22:23 -0700 | [diff] [blame] | 206 | return installNewLock(index, /*doWtf=*/ false); |
| 207 | } |
| 208 | |
| 209 | public static Object installNewLock(int index, boolean doWtf) { |
Jeff Sharkey | 5f3e934 | 2017-03-13 14:53:11 -0600 | [diff] [blame] | 210 | final Object lock = new Object(); |
Makoto Onuki | eed5b5a | 2018-03-13 14:22:23 -0700 | [diff] [blame] | 211 | installLock(lock, index, doWtf); |
Jeff Sharkey | 5f3e934 | 2017-03-13 14:53:11 -0600 | [diff] [blame] | 212 | return lock; |
Jeff Sharkey | 3d1cb6a | 2016-02-27 21:10:34 -0700 | [diff] [blame] | 213 | } |
| 214 | |
| 215 | private static String lockToString(Object lock) { |
| 216 | final LockInfo info = sKnown.get(lock); |
Makoto Onuki | eed5b5a | 2018-03-13 14:22:23 -0700 | [diff] [blame] | 217 | if (info != null && !TextUtils.isEmpty(info.label)) { |
Jeff Sharkey | 3d1cb6a | 2016-02-27 21:10:34 -0700 | [diff] [blame] | 218 | return info.label; |
| 219 | } else { |
| 220 | return "0x" + Integer.toHexString(System.identityHashCode(lock)); |
| 221 | } |
| 222 | } |
| 223 | |
Jeff Sharkey | 5f3e934 | 2017-03-13 14:53:11 -0600 | [diff] [blame] | 224 | private static String lockToString(int index) { |
| 225 | switch (index) { |
| 226 | case INDEX_APP_OPS: return "APP_OPS"; |
| 227 | case INDEX_POWER: return "POWER"; |
| 228 | case INDEX_USER: return "USER"; |
| 229 | case INDEX_PACKAGES: return "PACKAGES"; |
| 230 | case INDEX_STORAGE: return "STORAGE"; |
| 231 | case INDEX_WINDOW: return "WINDOW"; |
| 232 | case INDEX_ACTIVITY: return "ACTIVITY"; |
Makoto Onuki | eed5b5a | 2018-03-13 14:22:23 -0700 | [diff] [blame] | 233 | case INDEX_DPMS: return "DPMS"; |
Jeff Sharkey | 5f3e934 | 2017-03-13 14:53:11 -0600 | [diff] [blame] | 234 | default: return Integer.toString(index); |
| 235 | } |
| 236 | } |
| 237 | |
Jeff Sharkey | 3d1cb6a | 2016-02-27 21:10:34 -0700 | [diff] [blame] | 238 | public static void dump(FileDescriptor fd, PrintWriter pw, String[] args) { |
| 239 | for (int i = 0; i < sKnown.size(); i++) { |
| 240 | final Object lock = sKnown.keyAt(i); |
| 241 | final LockInfo info = sKnown.valueAt(i); |
| 242 | pw.println("Lock " + lockToString(lock) + ":"); |
| 243 | for (int j = 0; j < info.children.size(); j++) { |
| 244 | pw.println(" Child " + lockToString(info.children.valueAt(j))); |
| 245 | } |
| 246 | pw.println(); |
| 247 | } |
| 248 | } |
| 249 | } |