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Fixes an edge case which leads to deadlock in ShortcutService

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ShortcutService uses two levels of synchronization lock, one on the
service-level, another on package-level. To prevent deadlock, we made an
implicit rule that a thread can never acquire service-level lock if they
were holding onto package-level lock.

An edge case emerges when we ran into "what a terrible failure",
service-level lock was acquired to increase wtf counter and capture
stack traces, regardless of the implicit rule mentioned above.

This CL solves the deadlock by using a separate lock in wtf.

Bug: 243880581
Test: manual
Change-Id: I136ed4018b07ae17591207c5c855e9d34082ae77
This commit is contained in:
Pinyao Ting
2022-09-01 11:19:31 -07:00
parent b4c3a06820
commit 30fed8c21b
1 changed files with 12 additions and 9 deletions
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21
services/core/java/com/android/server/pm/ShortcutService.java
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@@ -280,6 +280,7 @@ public class ShortcutService extends IShortcutService.Stub {
private final Object mLock = new Object();
private final Object mNonPersistentUsersLock = new Object();
private final Object mWtfLock = new Object();
private static List<ResolveInfo> EMPTY_RESOLVE_INFO = new ArrayList<>(0);
@@ -444,10 +445,10 @@ public class ShortcutService extends IShortcutService.Stub {
@interface ShortcutOperation {
}
@GuardedBy("mLock")
@GuardedBy("mWtfLock")
private int mWtfCount = 0;
@GuardedBy("mLock")
@GuardedBy("mWtfLock")
private Exception mLastWtfStacktrace;
@GuardedBy("mLock")
@@ -4727,13 +4728,15 @@ public class ShortcutService extends IShortcutService.Stub {
mStatLogger.dump(pw, " ");
pw.println();
pw.print(" #Failures: ");
pw.println(mWtfCount);
synchronized (mWtfLock) {
pw.println();
pw.print(" #Failures: ");
pw.println(mWtfCount);
if (mLastWtfStacktrace != null) {
pw.print(" Last failure stack trace: ");
pw.println(Log.getStackTraceString(mLastWtfStacktrace));
if (mLastWtfStacktrace != null) {
pw.print(" Last failure stack trace: ");
pw.println(Log.getStackTraceString(mLastWtfStacktrace));
}
}
pw.println();
@@ -5148,7 +5151,7 @@ public class ShortcutService extends IShortcutService.Stub {
if (e == null) {
e = new RuntimeException("Stacktrace");
}
synchronized (mLock) {
synchronized (mWtfLock) {
mWtfCount++;
mLastWtfStacktrace = new Exception("Last failure was logged here:");
}