Kernel: Add a syscall to clear the profiling buffer

While profiling all processes the profile buffer lives forever.
Once you have copied the profile to disk, there's no need to keep it
in memory. This syscall surfaces the ability to clear that buffer.

Kernel/Syscalls/profiling.cpp

@@ -67,6 +67,8 @@ KResultOr<int> Process::sys$profiling_enable(pid_t pid)
 
 KResultOr<int> Process::sys$profiling_disable(pid_t pid)
 {
+    REQUIRE_NO_PROMISES;
+
     if (pid == -1) {
         if (!is_superuser())
             return EPERM;
@@ -87,4 +89,35 @@ KResultOr<int> Process::sys$profiling_disable(pid_t pid)
     return 0;
 }
 
+KResultOr<int> Process::sys$profiling_free_buffer(pid_t pid)
+{
+    REQUIRE_NO_PROMISES;
+
+    if (pid == -1) {
+        if (!is_superuser())
+            return EPERM;
+
+        OwnPtr<PerformanceEventBuffer> perf_events;
+
+        {
+            ScopedCritical critical;
+
+            perf_events = g_global_perf_events;
+            g_global_perf_events = nullptr;
+        }
+
+        return 0;
+    }
+
+    ScopedSpinLock lock(g_processes_lock);
+    auto process = Process::from_pid(pid);
+    if (!process)
+        return ESRCH;
+    if (!is_superuser() && process->uid() != euid())
+        return EPERM;
+    if (process->is_profiling())
+        return EINVAL;
+    process->delete_perf_events_buffer();
+    return 0;
+}
 }