Ticket #11482: 0001-user-mutex-dequeue-waiters-when-waking-them-up.patch

src/system/kernel/locks/user_mutex.cpp

@@ -131 +131 @@
     status_t error = waitEntry.Wait(flags, timeout);
     locker.Lock();
 
-    // dequeue
-    if (!remove_user_mutex_entry(&entry)) {
+    // dequeue if we weren't woken up
+    if (!entry.locked && !remove_user_mutex_entry(&entry)) {
         // no one is waiting anymore -- clear the waiting flag
         atomic_and(mutex, ~(int32)B_USER_MUTEX_WAITING);
     }
@@ -150 +150 @@
 static void
 user_mutex_unlock_locked(int32* mutex, addr_t physicalAddress, uint32 flags)
 {
-    if (UserMutexEntry* entry = sUserMutexTable.Lookup(physicalAddress)) {
-        // Someone is waiting -- set the locked flag. It might still be set,
-        // but when using userland atomic operations, the caller will usually
-        // have cleared it already.
-        int32 oldValue = atomic_or(mutex, B_USER_MUTEX_LOCKED);
-
-        // unblock the first thread
-        entry->locked = true;
-        entry->condition.NotifyOne();
-
-        if ((flags & B_USER_MUTEX_UNBLOCK_ALL) != 0
-                || (oldValue & B_USER_MUTEX_DISABLED) != 0) {
-            // unblock all the other waiting threads as well
-            for (UserMutexEntryList::Iterator it
-                    = entry->otherEntries.GetIterator();
-                UserMutexEntry* otherEntry = it.Next();) {
-                otherEntry->locked = true;
-                otherEntry->condition.NotifyOne();
-            }
-        }
-    } else {
+    UserMutexEntry* entry = sUserMutexTable.Lookup(physicalAddress);
+    if (entry == NULL) {
         // no one is waiting -- clear locked flag
         atomic_and(mutex, ~(int32)B_USER_MUTEX_LOCKED);
+        return;
+    }
+
+    // Someone is waiting -- set the locked flag. It might still be set,
+    // but when using userland atomic operations, the caller will usually
+    // have cleared it already.
+    int32 oldValue = atomic_or(mutex, B_USER_MUTEX_LOCKED);
+
+    // unblock the first thread
+    entry->locked = true;
+    entry->condition.NotifyOne();
+
+    if ((flags & B_USER_MUTEX_UNBLOCK_ALL) != 0
+            || (oldValue & B_USER_MUTEX_DISABLED) != 0) {
+        // unblock and dequeue all the other waiting threads as well
+        while (UserMutexEntry* otherEntry = entry->otherEntries.RemoveHead()) {
+            otherEntry->locked = true;
+            otherEntry->condition.NotifyOne();
+        }
+
+        // dequeue the first thread and mark the mutex uncontended
+        sUserMutexTable.Remove(entry);
+        atomic_and(mutex, ~(int32)B_USER_MUTEX_WAITING);
+    } else {
+        bool otherWaiters = remove_user_mutex_entry(entry);
+        if (!otherWaiters)
+            atomic_and(mutex, ~(int32)B_USER_MUTEX_WAITING);
     }
 }