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Ensure mutation to multiple objects is done atomically

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Acquire both parent and child locks before mutation begins.
This ensures no concurrent mutation is possible on another thread.

Bug: 161954235
Test: atest StagedInstallTest AtomicInstallTest
Change-Id: If4b83ef83bbe7e85e91a6b8f16e01d4dc0d6d8e6
This commit is contained in:
JW Wang
2020-07-27 14:52:28 +08:00
parent be70384952
commit acae3c0f3b
1 changed files with 59 additions and 17 deletions
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76
services/core/java/com/android/server/pm/PackageInstallerSession.java
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@@ -157,6 +157,7 @@ import java.util.Arrays;
import java.util.List;
import java.util.Objects;
import java.util.Set;
import java.util.concurrent.atomic.AtomicBoolean;
import java.util.concurrent.atomic.AtomicInteger;
public class PackageInstallerSession extends IPackageInstallerSession.Stub {
@@ -262,6 +263,12 @@ public class PackageInstallerSession extends IPackageInstallerSession.Stub {
private final Object mLock = new Object();
/**
* Used to detect and reject concurrent access to this session object to ensure mutation
* to multiple objects like {@link #addChildSessionId} are done atomically.
*/
private final AtomicBoolean mTransactionLock = new AtomicBoolean(false);
/** Timestamp of the last time this session changed state */
@GuardedBy("mLock")
private long updatedMillis;
@@ -3073,39 +3080,74 @@ public class PackageInstallerSession extends IPackageInstallerSession.Stub {
}
}
private void acquireTransactionLock() {
if (!mTransactionLock.compareAndSet(false, true)) {
throw new UnsupportedOperationException("Concurrent access not supported");
}
}
private void releaseTransactionLock() {
mTransactionLock.compareAndSet(true, false);
}
@Override
public void addChildSessionId(int childSessionId) {
final PackageInstallerSession childSession = mSessionProvider.getSession(childSessionId);
if (childSession == null || !childSession.canBeAddedAsChild(sessionId)) {
if (childSession == null) {
throw new IllegalStateException("Unable to add child session " + childSessionId
+ " as it does not exist or is in an invalid state.");
+ " as it does not exist.");
}
synchronized (mLock) {
assertCallerIsOwnerOrRootLocked();
assertPreparedAndNotSealedLocked("addChildSessionId");
final int indexOfSession = mChildSessionIds.indexOfKey(childSessionId);
if (indexOfSession >= 0) {
return;
try {
acquireTransactionLock();
childSession.acquireTransactionLock();
if (!childSession.canBeAddedAsChild(sessionId)) {
throw new IllegalStateException("Unable to add child session " + childSessionId
+ " as it is in an invalid state.");
}
childSession.setParentSessionId(this.sessionId);
addChildSessionIdLocked(childSessionId);
synchronized (mLock) {
assertCallerIsOwnerOrRootLocked();
assertPreparedAndNotSealedLocked("addChildSessionId");
final int indexOfSession = mChildSessionIds.indexOfKey(childSessionId);
if (indexOfSession >= 0) {
return;
}
childSession.setParentSessionId(this.sessionId);
addChildSessionIdLocked(childSessionId);
}
} finally {
releaseTransactionLock();
childSession.releaseTransactionLock();
}
}
@Override
public void removeChildSessionId(int sessionId) {
final PackageInstallerSession session = mSessionProvider.getSession(sessionId);
synchronized (mLock) {
final int indexOfSession = mChildSessionIds.indexOfKey(sessionId);
try {
acquireTransactionLock();
if (session != null) {
session.setParentSessionId(SessionInfo.INVALID_ID);
session.acquireTransactionLock();
}
if (indexOfSession < 0) {
// not added in the first place; no-op
return;
synchronized (mLock) {
final int indexOfSession = mChildSessionIds.indexOfKey(sessionId);
if (session != null) {
session.setParentSessionId(SessionInfo.INVALID_ID);
}
if (indexOfSession < 0) {
// not added in the first place; no-op
return;
}
mChildSessionIds.removeAt(indexOfSession);
}
} finally {
releaseTransactionLock();
if (session != null) {
session.releaseTransactionLock();
}
mChildSessionIds.removeAt(indexOfSession);
}
}