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kernel/user_mutex: Check that a thread was actually unblocked during handoff.

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Otherwise, we will deadlock.

I don't know that this has ever actually occurred; it is very unlikely
due to the write-lock acquisition before unblocking. It could only
occur if a SIGINT was delivered or timeout+wakeup occurred at just
the right moment.
This commit is contained in:
Augustin Cavalier
2023-07-25 15:33:07 -04:00
parent aca21731ff
commit b3b7b89334
1 changed files with 4 additions and 4 deletions
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src/system/kernel/locks/user_mutex.cpp
+4 -4
View File
@@ -402,10 +402,11 @@ user_mutex_unblock(UserMutexEntry* entry, int32* mutex, uint32 flags, bool isWir
if ((flags & B_USER_MUTEX_UNBLOCK_ALL) != 0 if ((flags & B_USER_MUTEX_UNBLOCK_ALL) != 0
|| (oldValue & B_USER_MUTEX_DISABLED) != 0) { || (oldValue & B_USER_MUTEX_DISABLED) != 0) {
// unblock and dequeue all the waiting threads // unblock all waiting threads
entry->condition.NotifyAll(B_OK); entry->condition.NotifyAll(B_OK);
} else { } else {
entry->condition.NotifyOne(B_OK); if (!entry->condition.NotifyOne(B_OK))
user_atomic_or(mutex, ~(int32)B_USER_MUTEX_LOCKED, isWired);
} }
if (entry->condition.EntriesCount() == 0) if (entry->condition.EntriesCount() == 0)
@@ -436,7 +437,7 @@ static void
user_mutex_sem_release(UserMutexEntry* entry, int32* sem, bool isWired) user_mutex_sem_release(UserMutexEntry* entry, int32* sem, bool isWired)
{ {
WriteLocker entryLocker(entry->lock); WriteLocker entryLocker(entry->lock);
if (entry->condition.EntriesCount() == 0) { if (entry->condition.NotifyOne(B_OK) == 0) {
// no waiters - mark as uncontended and release // no waiters - mark as uncontended and release
int32 oldValue = user_atomic_get(sem, isWired); int32 oldValue = user_atomic_get(sem, isWired);
while (true) { while (true) {
@@ -448,7 +449,6 @@ user_mutex_sem_release(UserMutexEntry* entry, int32* sem, bool isWired)
} }
} }
entry->condition.NotifyOne(B_OK);
if (entry->condition.EntriesCount() == 0) { if (entry->condition.EntriesCount() == 0) {
// mark the semaphore uncontended // mark the semaphore uncontended
user_atomic_test_and_set(sem, 0, -1, isWired); user_atomic_test_and_set(sem, 0, -1, isWired);