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frameworks/base: acquire lock on am only when needed

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appendDropBoxProcessHeaders acquires a lock on am while accessing
ProcessRecord (even if it is null). Watchdog thread ends up invoking
this function (with a null ProcessRecord) to add the stack file to
dropbox. This function would block if and when the watchdog thread is
invoked due to unavailability of lock on am resulting in a deadlock.
This would prevent watchdog from killing system_server.

Change-Id: Ieb34b767779cb587e0c5f536b9b7ba44fb9a28d9
This commit is contained in:
Vairavan Srinivasan
2011-02-14 20:45:59 -08:00
parent 7d234fabe6
commit 68a4e0a38f
1 changed files with 11 additions and 4 deletions
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15
services/java/com/android/server/am/ActivityManagerService.java
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@@ -6730,18 +6730,25 @@ public final class ActivityManagerService extends ActivityManagerNative
* to append various headers to the dropbox log text.
*/
private void appendDropBoxProcessHeaders(ProcessRecord process, StringBuilder sb) {
// Watchdog thread ends up invoking this function (with
// a null ProcessRecord) to add the stack file to dropbox.
// Do not acquire a lock on this (am) in such cases, as it
// could cause a potential deadlock, if and when watchdog
// is invoked due to unavailability of lock on am and it
// would prevent watchdog from killing system_server.
if (process == null) {
sb.append("Process: system_server\n");
return;
}
// Note: ProcessRecord 'process' is guarded by the service
// instance. (notably process.pkgList, which could otherwise change
// concurrently during execution of this method)
synchronized (this) {
if (process == null || process.pid == MY_PID) {
if (process.pid == MY_PID) {
sb.append("Process: system_server\n");
} else {
sb.append("Process: ").append(process.processName).append("\n");
}
if (process == null) {
return;
}
int flags = process.info.flags;
IPackageManager pm = AppGlobals.getPackageManager();
sb.append("Flags: 0x").append(Integer.toString(flags, 16)).append("\n");