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Kernel/SMP: Make entering/leaving critical sections multi-processor safe

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By making these functions static we close a window where we could get
preempted after calling Processor::current() and move to another
processor.

Co-authored-by: Tom <tomut@yahoo.com>
This commit is contained in:
Andreas Kling 2021-08-10 01:16:08 +02:00
parent 369e3da6a2
commit 9babb92a4b
11 changed files with 82 additions and 53 deletions
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12
Kernel/Arch/x86/common/Processor.cpp
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@ -613,7 +613,7 @@ void Processor::exit_trap(TrapFrame& trap)
// to trigger a context switch while we're executing this function
// See the comment at the end of the function why we don't use
// ScopedCritical here.
m_in_critical++;
m_in_critical = m_in_critical + 1;
VERIFY(m_in_irq >= trap.prev_irq_level);
m_in_irq = trap.prev_irq_level;
@ -646,11 +646,13 @@ void Processor::exit_trap(TrapFrame& trap)
current_thread->update_time_scheduled(Scheduler::current_time(), true, false);
}
VERIFY_INTERRUPTS_DISABLED();
// Leave the critical section without actually enabling interrupts.
// We don't want context switches to happen until we're explicitly
// triggering a switch in check_invoke_scheduler.
auto new_critical = m_in_critical.fetch_sub(1) - 1;
if (!m_in_irq && !new_critical)
m_in_critical = m_in_critical - 1;
if (!m_in_irq && !m_in_critical)
check_invoke_scheduler();
}
@ -730,7 +732,7 @@ ProcessorMessage& Processor::smp_get_from_pool()
u32 Processor::smp_wake_n_idle_processors(u32 wake_count)
{
VERIFY(Processor::current().in_critical());
VERIFY(Processor::in_critical());
VERIFY(wake_count > 0);
if (!s_smp_enabled)
return 0;
@ -1311,7 +1313,7 @@ void Processor::assume_context(Thread& thread, FlatPtr flags)
Scheduler::prepare_after_exec();
// in_critical() should be 2 here. The critical section in Process::exec
// and then the scheduler lock
VERIFY(Processor::current().in_critical() == 2);
VERIFY(Processor::in_critical() == 2);
do_assume_context(&thread, flags);