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Kernel: Always return from Thread::wait_on

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We need to always return from Thread::wait_on, even when a thread
is being killed. This is necessary so that the kernel call stack
can clean up and release references held by it. Then, right before
transitioning back to user mode, we check if the thread is
supposed to die, and at that point change the thread state to
Dying to prevent further scheduling of this thread.

This addresses some possible resource leaks similar to #3073
This commit is contained in:
Tom 2020-08-10 14:05:24 -06:00 • committed by Andreas Kling
parent 1f7190d3bd
commit 49d5232f33
4 changed files with 28 additions and 33 deletions
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15
Kernel/Scheduler.cpp
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@ -365,6 +365,21 @@ bool Scheduler::pick_next()
ScopedSpinLock lock(g_scheduler_lock);
if (current_thread->should_die() && current_thread->state() == Thread::Running) {
// Rather than immediately killing threads, yanking the kernel stack
// away from them (which can lead to e.g. reference leaks), we always
// allow Thread::wait_on to return. This allows the kernel stack to
// clean up and eventually we'll get here shortly before transitioning
// back to user mode (from Processor::exit_trap). At this point we
// no longer want to schedule this thread. We can't wait until
// Scheduler::enter_current because we don't want to allow it to
// transition back to user mode.
#ifdef SCHEDULER_DEBUG
dbg() << "Scheduler[" << Processor::current().id() << "]: Thread " << *current_thread << " is dying";
#endif
current_thread->set_state(Thread::Dying);
}
// Check and unblock threads whose wait conditions have been met.
Scheduler::for_each_nonrunnable([&](Thread& thread) {
thread.consider_unblock(now_sec, now_usec);