Kernel: Fix Lock race causing infinite spinning between two threads

We need to account for how many shared lock instances the current
thread owns, so that we can properly release such references when
yielding execution.

We also need to release the process lock when donating.

1 files changed, 2 insertions, 5 deletions

diff --git a/Kernel/Syscalls/sched.cpp b/Kernel/Syscalls/sched.cpp
index 8882a0c627..f497a26ca0 100644
--- a/Kernel/Syscalls/sched.cpp
+++ b/Kernel/Syscalls/sched.cpp
@@ -41,14 +41,11 @@ int Process::sys$donate(pid_t tid)
     if (tid < 0)
         return -EINVAL;
 
-    // We don't strictly need to grab the scheduler lock here, but it
-    // will close a race where we can find the thread but it disappears
-    // before we call Scheduler::donate_to.
-    ScopedSpinLock lock(g_scheduler_lock);
+    ScopedCritical critical;
     auto thread = Thread::from_tid(tid);
     if (!thread || thread->pid() != pid())
         return -ESRCH;
-    Scheduler::donate_to(thread, "sys$donate");
+    Thread::current()->donate_without_holding_big_lock(thread, "sys$donate");
     return 0;
 }