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kernel/user_mutex: Fix race in user_mutex_sem_release.

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We need to be sure nothing will start waiting before marking the
semaphore as uncontended.

Fixes a deadlock observed in libuv.
This commit is contained in:
Augustin Cavalier
2023-07-25 15:21:00 -04:00
parent ae65daec10
commit 2cc89328fa
1 changed files with 3 additions and 3 deletions
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src/system/kernel/locks/user_mutex.cpp
+3 -3
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@@ -435,7 +435,8 @@ user_mutex_sem_acquire_locked(UserMutexEntry* entry, int32* sem,
static void static void
user_mutex_sem_release(UserMutexEntry* entry, int32* sem, bool isWired) user_mutex_sem_release(UserMutexEntry* entry, int32* sem, bool isWired)
{ {
if (entry == NULL) { WriteLocker entryLocker(entry->lock);
if (entry->condition.EntriesCount() == 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) {
@@ -447,7 +448,6 @@ user_mutex_sem_release(UserMutexEntry* entry, int32* sem, bool isWired)
} }
} }
WriteLocker entryLocker(entry->lock);
entry->condition.NotifyOne(B_OK); entry->condition.NotifyOne(B_OK);
if (entry->condition.EntriesCount() == 0) { if (entry->condition.EntriesCount() == 0) {
// mark the semaphore uncontended // mark the semaphore uncontended
@@ -706,7 +706,7 @@ _user_mutex_sem_release(int32* sem)
return error; return error;
UserMutexEntry* entry = get_user_mutex_entry(context, UserMutexEntry* entry = get_user_mutex_entry(context,
wiringInfo.physicalAddress, true); wiringInfo.physicalAddress);
{ {
user_mutex_sem_release(entry, sem, true); user_mutex_sem_release(entry, sem, true);
} }