Andreas Kling cc9ed31c37 Kernel: Don't mark current thread as inactive after successful exec() ...

At the end of sys$execve(), we perform a context switch from the old
executable into the new executable.

However, the Kernel::Thread object we are switching to is the *same*
thread as the one we are switching from. So we must not assume the
from_thread and to_thread are different threads.

We had a bug caused by this misconception, where the "from" thread would
always get marked as "inactive" when switching to a new thread.
This meant that threads would always get switched into "inactive" mode
on first context switch into them.

If a thread then tried blocking on a kernel mutex within its first time
slice, we'd end up in Thread::block(Mutex&) with an inactive thread.

Once a thread is inactive, the scheduler believes it's okay to
reactivate the thread (by scheduling it.) If a thread got re-scheduled
prematurely while setting up a mutex block, things would fall apart and
we'd crash in Thread::block() due to the thread state being "Runnable"
instead of the expected "Running".

2022-01-30 16:21:59 +01:00

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