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Kernel/SMP: Don't enable interrupts in Processor::exit_trap

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Enter a critical section in Processor::exit_trap so that processing
SMP messages doesn't enable interrupts upon leaving. We need to delay
this until the end where we call into the Scheduler if exiting the
trap results in being outside of a critical section and irq handler.

Co-authored-by: Tom <tomut@yahoo.com>
This commit is contained in:
Andreas Kling 2021-08-08 22:22:38 +02:00
parent cd0fc7f52c
commit f27e7bbbf4
3 changed files with 27 additions and 6 deletions
Download patch file Download diff file Expand all files Collapse all files

25
Kernel/Arch/x86/common/Processor.cpp
View file

@ -602,6 +602,14 @@ void Processor::exit_trap(TrapFrame& trap)
{
VERIFY_INTERRUPTS_DISABLED();
VERIFY(&Processor::current() == this);
// Temporarily enter a critical section. This is to prevent critical
// sections entered and left within e.g. smp_process_pending_messages
// 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++;
VERIFY(m_in_irq >= trap.prev_irq_level);
m_in_irq = trap.prev_irq_level;
@ -628,7 +636,11 @@ void Processor::exit_trap(TrapFrame& trap)
current_thread->update_time_scheduled(Scheduler::current_time(), true, false);
}
if (!m_in_irq && !m_in_critical)
// 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)
check_invoke_scheduler();
}
@ -636,6 +648,8 @@ void Processor::check_invoke_scheduler()
{
VERIFY(!m_in_irq);
VERIFY(!m_in_critical);
VERIFY_INTERRUPTS_DISABLED();
VERIFY(&Processor::current() == this);
if (m_invoke_scheduler_async && m_scheduler_initialized) {
m_invoke_scheduler_async = false;
Scheduler::invoke_async();
@ -1191,6 +1205,10 @@ extern "C" void context_first_init([[maybe_unused]] Thread* from_thread, [[maybe
Scheduler::enter_current(*from_thread, true);
auto in_critical = to_thread->saved_critical();
VERIFY(in_critical > 0);
Processor::current().restore_in_critical(in_critical);
// 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 notify the scheduler so that it can release
@ -1249,7 +1267,10 @@ extern "C" void enter_thread_context(Thread* from_thread, Thread* to_thread)
write_cr3(to_regs.cr3);
to_thread->set_cpu(processor.get_id());
processor.restore_in_critical(to_thread->saved_critical());
auto in_critical = to_thread->saved_critical();
VERIFY(in_critical > 0);
processor.restore_in_critical(in_critical);
if (has_fxsr)
asm volatile("fxrstor %0" ::"m"(to_thread->fpu_state()));

4
Kernel/Arch/x86/i386/Processor.cpp
View file

@ -185,6 +185,8 @@ void Processor::switch_context(Thread*& from_thread, Thread*& to_thread)
VERIFY(is_kernel_mode());
dbgln_if(CONTEXT_SWITCH_DEBUG, "switch_context --> switching out of: {} {}", VirtualAddress(from_thread), *from_thread);
// m_in_critical is restored in enter_thread_context
from_thread->save_critical(m_in_critical);
// clang-format off
@ -230,8 +232,6 @@ void Processor::switch_context(Thread*& from_thread, Thread*& to_thread)
// clang-format on
dbgln_if(CONTEXT_SWITCH_DEBUG, "switch_context <-- from {} {} to {} {}", VirtualAddress(from_thread), *from_thread, VirtualAddress(to_thread), *to_thread);
Processor::current().restore_in_critical(to_thread->saved_critical());
}
UNMAP_AFTER_INIT void Processor::initialize_context_switching(Thread& initial_thread)

4
Kernel/Arch/x86/x86_64/Processor.cpp
View file

@ -169,6 +169,8 @@ void Processor::switch_context(Thread*& from_thread, Thread*& to_thread)
VERIFY(is_kernel_mode());
dbgln_if(CONTEXT_SWITCH_DEBUG, "switch_context --> switching out of: {} {}", VirtualAddress(from_thread), *from_thread);
// m_in_critical is restored in enter_thread_context
from_thread->save_critical(m_in_critical);
// clang-format off
@ -238,8 +240,6 @@ void Processor::switch_context(Thread*& from_thread, Thread*& to_thread)
// clang-format on
dbgln_if(CONTEXT_SWITCH_DEBUG, "switch_context <-- from {} {} to {} {}", VirtualAddress(from_thread), *from_thread, VirtualAddress(to_thread), *to_thread);
Processor::current().restore_in_critical(to_thread->saved_critical());
}
UNMAP_AFTER_INIT void Processor::initialize_context_switching(Thread& initial_thread)