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Kernel: Fix signal delivery

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When delivering urgent signals to the current thread
we need to check if we should be unblocked, and if not
we need to yield to another process.

We also need to make sure that we suppress context switches
during Process::exec() so that we don't clobber the registers
that it sets up (eip mainly) by a context switch. To be able
to do that we add the concept of a critical section, which are
similar to Process::m_in_irq but different in that they can be
requested at any time. Calls to Scheduler::yield and
Scheduler::donate_to will return instantly without triggering
a context switch, but the processor will then asynchronously
trigger a context switch once the critical section is left.
This commit is contained in:
Tom 2020-07-03 05:19:50 -06:00 • committed by Andreas Kling
parent a308b176ce
commit e373e5f007
12 changed files with 242 additions and 95 deletions
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46
Kernel/Process.cpp
View file

@ -84,10 +84,10 @@
#include <LibELF/Validation.h>
#include <LibKeyboard/CharacterMapData.h>
#define PROCESS_DEBUG
//#define PROCESS_DEBUG
//#define DEBUG_POLL_SELECT
//#define DEBUG_IO
#define TASK_DEBUG
//#define TASK_DEBUG
//#define FORK_DEBUG
//#define EXEC_DEBUG
//#define SIGNAL_DEBUG
@ -821,9 +821,10 @@ void Process::kill_all_threads()
});
}
int Process::do_exec(NonnullRefPtr<FileDescription> main_program_description, Vector<String> arguments, Vector<String> environment, RefPtr<FileDescription> interpreter_description)
int Process::do_exec(NonnullRefPtr<FileDescription> main_program_description, Vector<String> arguments, Vector<String> environment, RefPtr<FileDescription> interpreter_description, Thread*& new_main_thread, u32& prev_flags)
{
ASSERT(is_ring3());
ASSERT(!Processor::current().in_critical());
auto path = main_program_description->absolute_path();
#ifdef EXEC_DEBUG
dbg() << "do_exec(" << path << ")";
@ -867,7 +868,7 @@ int Process::do_exec(NonnullRefPtr<FileDescription> main_program_description, Ve
{
// Need to make sure we don't swap contexts in the middle
InterruptDisabler disabler;
ScopedCritical critical;
old_page_directory = move(m_page_directory);
old_regions = move(m_regions);
m_page_directory = PageDirectory::create_for_userspace(*this);
@ -910,7 +911,7 @@ int Process::do_exec(NonnullRefPtr<FileDescription> main_program_description, Ve
ArmedScopeGuard rollback_regions_guard([&]() {
ASSERT(Process::current() == this);
// Need to make sure we don't swap contexts in the middle
InterruptDisabler disabler;
ScopedCritical critical;
m_page_directory = move(old_page_directory);
m_regions = move(old_regions);
MM.enter_process_paging_scope(*this);
@ -963,6 +964,7 @@ int Process::do_exec(NonnullRefPtr<FileDescription> main_program_description, Ve
master_tls_alignment = alignment;
return master_tls_region->vaddr().as_ptr();
};
ASSERT(!Processor::current().in_critical());
bool success = loader->load();
if (!success) {
klog() << "do_exec: Failure loading " << path.characters();
@ -1026,7 +1028,7 @@ int Process::do_exec(NonnullRefPtr<FileDescription> main_program_description, Ve
}
}
Thread* new_main_thread = nullptr;
new_main_thread = nullptr;
if (&current_thread->process() == this) {
new_main_thread = current_thread;
} else {
@ -1041,11 +1043,10 @@ int Process::do_exec(NonnullRefPtr<FileDescription> main_program_description, Ve
// and we don't want to deal with faults after this point.
u32 new_userspace_esp = new_main_thread->make_userspace_stack_for_main_thread(move(arguments), move(environment));
// We cli() manually here because we don't want to get interrupted between do_exec() and Processor::assume_context().
// The reason is that the task redirection we've set up above will be clobbered by the timer IRQ.
// We cli() manually here because we don't want to get interrupted between do_exec()
// and Processor::assume_context() or the next context switch.
// If we used an InterruptDisabler that sti()'d on exit, we might timer tick'd too soon in exec().
if (&current_thread->process() == this)
cli();
Processor::current().enter_critical(prev_flags);
// NOTE: Be careful to not trigger any page faults below!
@ -1059,7 +1060,6 @@ int Process::do_exec(NonnullRefPtr<FileDescription> main_program_description, Ve
new_main_thread->make_thread_specific_region({});
new_main_thread->reset_fpu_state();
// NOTE: if a context switch were to happen, tss.eip and tss.esp would get overwritten!!!
auto& tss = new_main_thread->m_tss;
tss.cs = GDT_SELECTOR_CODE3 | 3;
tss.ds = GDT_SELECTOR_DATA3 | 3;
@ -1073,7 +1073,7 @@ int Process::do_exec(NonnullRefPtr<FileDescription> main_program_description, Ve
tss.ss2 = m_pid;
#ifdef TASK_DEBUG
klog() << "Process exec'd " << path.characters() << " @ " << String::format("%p", entry_eip);
klog() << "Process " << VirtualAddress(this) << " thread " << VirtualAddress(new_main_thread) << " exec'd " << path.characters() << " @ " << String::format("%p", entry_eip);
#endif
if (was_profiling)
@ -1081,6 +1081,8 @@ int Process::do_exec(NonnullRefPtr<FileDescription> main_program_description, Ve
new_main_thread->set_state(Thread::State::Skip1SchedulerPass);
big_lock().force_unlock_if_locked();
ASSERT_INTERRUPTS_DISABLED();
ASSERT(Processor::current().in_critical());
return 0;
}
@ -1249,26 +1251,26 @@ int Process::exec(String path, Vector<String> arguments, Vector<String> environm
// The bulk of exec() is done by do_exec(), which ensures that all locals
// are cleaned up by the time we yield-teleport below.
int rc = do_exec(move(description), move(arguments), move(environment), move(interpreter_description));
Thread* new_main_thread = nullptr;
u32 prev_flags = 0;
int rc = do_exec(move(description), move(arguments), move(environment), move(interpreter_description), new_main_thread, prev_flags);
m_exec_tid = 0;
if (rc < 0)
return rc;
auto current_thread = Thread::current();
if (m_wait_for_tracer_at_next_execve) {
ASSERT(current_thread->state() == Thread::State::Skip1SchedulerPass);
// State::Skip1SchedulerPass is irrelevant since we block the thread
current_thread->set_state(Thread::State::Running);
current_thread->send_urgent_signal_to_self(SIGSTOP);
}
ASSERT_INTERRUPTS_DISABLED();
ASSERT(Processor::current().in_critical());
if (&current_thread->process() == this) {
auto current_thread = Thread::current();
if (current_thread == new_main_thread) {
current_thread->set_state(Thread::State::Running);
Processor::assume_context(*current_thread);
Processor::assume_context(*current_thread, prev_flags);
ASSERT_NOT_REACHED();
}
Processor::current().leave_critical(prev_flags);
return 0;
}