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Kernel: Various context switch fixes

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These changes solve a number of problems with the software
context swithcing:

* The scheduler lock really should be held throughout context switches
* Transitioning from the initial (idle) thread to another needs to
  hold the scheduler lock
* Transitioning from a dying thread to another also needs to hold
  the scheduler lock
* Dying threads cannot necessarily be finalized if they haven't
  switched out of it yet, so flag them as active while a processor
  is running it (the Running state may be switched to Dying while
  it still is actually running)
This commit is contained in:
Tom 2020-07-05 14:32:07 -06:00 • committed by Andreas Kling
parent 49f5069b76
commit 2a82a25fec
9 changed files with 235 additions and 89 deletions
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28
Kernel/Arch/i386/CPU.cpp
View file

@ -1035,10 +1035,10 @@ extern "C" void enter_thread_context(Thread* from_thread, Thread* to_thread)
#define ENTER_THREAD_CONTEXT_ARGS_SIZE (2 * 4) // to_thread, from_thread
void Processor::switch_context(Thread* from_thread, Thread* to_thread)
void Processor::switch_context(Thread*& from_thread, Thread*& to_thread)
{
ASSERT(!in_irq());
ASSERT(!m_in_critical);
ASSERT(m_in_critical == 1);
ASSERT(is_kernel_mode());
#ifdef CONTEXT_SWITCH_DEBUG
dbg() << "switch_context --> switching out of: " << VirtualAddress(from_thread) << " " << *from_thread;
@ -1096,13 +1096,23 @@ extern "C" void context_first_init(Thread* from_thread, Thread* to_thread, TrapF
(void)to_thread;
(void)trap;
ASSERT(to_thread == Thread::current());
#ifdef CONTEXT_SWITCH_DEBUG
dbg() << "switch_context <-- from " << VirtualAddress(from_thread) << " " << *from_thread << " to " << VirtualAddress(to_thread) << " " << *to_thread << " (context_first_init)";
#endif
ASSERT(to_thread == Thread::current());
Scheduler::enter_current(*from_thread);
if (to_thread->process().wait_for_tracer_at_next_execve()) {
to_thread->send_urgent_signal_to_self(SIGSTOP);
}
// Since we got here and don't have Scheduler::context_switch in the
// call stack (because this is the first time we switched into this
// context), we need to unlock the scheduler lock manually. We're
// using the flags initially set up by init_context
g_scheduler_lock.unlock(trap->regs->eflags);
}
extern "C" void thread_context_first_enter(void);
@ -1124,10 +1134,12 @@ asm(
u32 Processor::init_context(Thread& thread, bool leave_crit)
{
ASSERT(is_kernel_mode());
ASSERT(g_scheduler_lock.is_locked());
if (leave_crit) {
ASSERT(in_critical());
m_in_critical--; // leave it without triggering anything
ASSERT(!in_critical());
// Leave the critical section we set up in in Process::exec,
// but because we still have the scheduler lock we should end up with 1
m_in_critical--; // leave it without triggering anything or restoring flags
ASSERT(in_critical() == 1);
}
const u32 kernel_stack_top = thread.kernel_stack_top();
@ -1213,7 +1225,6 @@ u32 Processor::init_context(Thread& thread, bool leave_crit)
extern "C" u32 do_init_context(Thread* thread, u32 flags)
{
ASSERT_INTERRUPTS_DISABLED();
ASSERT(Processor::current().in_critical());
thread->tss().eflags = flags;
return Processor::current().init_context(*thread, true);
}
@ -1246,6 +1257,9 @@ void Processor::assume_context(Thread& thread, u32 flags)
dbg() << "Assume context for thread " << VirtualAddress(&thread) << " " << thread;
#endif
ASSERT_INTERRUPTS_DISABLED();
// in_critical() should be 2 here. The critical section in Process::exec
// and then the scheduler lock
ASSERT(Processor::current().in_critical() == 2);
do_assume_context(&thread, flags);
ASSERT_NOT_REACHED();
}

26
Kernel/Arch/i386/CPU.h
View file

@ -751,6 +751,30 @@ public:
}
if (prev_flags & 0x200)
sti();
else
cli();
}
ALWAYS_INLINE u32 clear_critical(u32& prev_flags, bool enable_interrupts)
{
u32 prev_crit = m_in_critical;
m_in_critical = 0;
prev_flags = cpu_flags();
if (!m_in_irq)
check_invoke_scheduler();
if (enable_interrupts)
sti();
return prev_crit;
}
ALWAYS_INLINE void restore_critical(u32 prev_crit, u32 prev_flags)
{
ASSERT(m_in_critical == 0);
m_in_critical = prev_crit;
if (prev_flags & 0x200)
sti();
else
cli();
}
ALWAYS_INLINE u32& in_critical() { return m_in_critical; }
@ -772,7 +796,7 @@ public:
void exit_trap(TrapFrame& trap);
[[noreturn]] void initialize_context_switching(Thread& initial_thread);
void switch_context(Thread* from_thread, Thread* to_thread);
void switch_context(Thread*& from_thread, Thread*& to_thread);
[[noreturn]] static void assume_context(Thread& thread, u32 flags);
u32 init_context(Thread& thread, bool leave_crit);
static bool get_context_frame_ptr(Thread& thread, u32& frame_ptr, u32& eip);