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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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61
Kernel/Arch/i386/CPU.cpp
View file

@ -828,6 +828,10 @@ void Processor::early_initialize(u32 cpu)
m_cpu = cpu;
m_in_irq = 0;
m_in_critical = 0;
m_invoke_scheduler_async = false;
m_scheduler_initialized = false;
m_idle_thread = nullptr;
m_current_thread = nullptr;
@ -961,9 +965,10 @@ extern "C" void enter_thread_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(is_kernel_mode());
#ifdef CONTEXT_SWITCH_DEBUG
dbg() << "switch_context --> switching out of: " << *from_thread;
dbg() << "switch_context --> switching out of: " << VirtualAddress(from_thread) << " " << *from_thread;
#endif
// Switch to new thread context, passing from_thread and to_thread
@ -1006,7 +1011,7 @@ void Processor::switch_context(Thread* from_thread, Thread* to_thread)
[to_thread] "a" (to_thread)
);
#ifdef CONTEXT_SWITCH_DEBUG
dbg() << "switch_context <-- from " << *from_thread << " to " << *to_thread;
dbg() << "switch_context <-- from " << VirtualAddress(from_thread) << " " << *from_thread << " to " << VirtualAddress(to_thread) << " " << *to_thread;
#endif
}
@ -1017,9 +1022,14 @@ extern "C" void context_first_init(Thread* from_thread, Thread* to_thread, TrapF
(void)from_thread;
(void)to_thread;
(void)trap;
ASSERT(to_thread == Thread::current());
#ifdef CONTEXT_SWITCH_DEBUG
dbg() << "switch_context <-- from " << *from_thread << " to " << *to_thread << " (context_first_init)";
dbg() << "switch_context <-- from " << VirtualAddress(from_thread) << " " << *from_thread << " to " << VirtualAddress(to_thread) << " " << *to_thread << " (context_first_init)";
#endif
if (to_thread->process().wait_for_tracer_at_next_execve()) {
to_thread->send_urgent_signal_to_self(SIGSTOP);
}
}
extern "C" void thread_context_first_enter(void);
@ -1038,9 +1048,15 @@ asm(
" jmp common_trap_exit \n"
);
u32 Processor::init_context(Thread& thread)
u32 Processor::init_context(Thread& thread, bool leave_crit)
{
ASSERT(is_kernel_mode());
if (leave_crit) {
ASSERT(in_critical());
m_in_critical--; // leave it without triggering anything
ASSERT(!in_critical());
}
const u32 kernel_stack_top = thread.kernel_stack_top();
u32 stack_top = kernel_stack_top;
@ -1098,7 +1114,10 @@ u32 Processor::init_context(Thread& thread)
*reinterpret_cast<u32*>(stack_top) = stack_top + 4;
#ifdef CONTEXT_SWITCH_DEBUG
dbg() << "init_context " << thread << " set up to execute at eip: " << VirtualAddress(tss.eip) << " esp: " << VirtualAddress(tss.esp) << " stack top: " << VirtualAddress(stack_top);
if (return_to_user)
dbg() << "init_context " << thread << " (" << VirtualAddress(&thread) << ") set up to execute at eip: " << String::format("%02x:%08x", iretframe.cs, (u32)tss.eip) << " esp: " << VirtualAddress(tss.esp) << " stack top: " << VirtualAddress(stack_top) << " user esp: " << String::format("%02x:%08x", iretframe.userspace_ss, (u32)iretframe.userspace_esp);
else
dbg() << "init_context " << thread << " (" << VirtualAddress(&thread) << ") set up to execute at eip: " << String::format("%02x:%08x", iretframe.cs, (u32)tss.eip) << " esp: " << VirtualAddress(tss.esp) << " stack top: " << VirtualAddress(stack_top);
#endif
// make switch_context() always first return to thread_context_first_enter()
@ -1118,24 +1137,29 @@ u32 Processor::init_context(Thread& thread)
}
extern "C" u32 do_init_context(Thread* thread)
extern "C" u32 do_init_context(Thread* thread, u32 flags)
{
return Processor::init_context(*thread);
ASSERT_INTERRUPTS_DISABLED();
ASSERT(Processor::current().in_critical());
thread->tss().eflags = flags;
return Processor::current().init_context(*thread, true);
}
extern "C" void do_assume_context(Thread* thread);
extern "C" void do_assume_context(Thread* thread, u32 flags);
asm(
".global do_assume_context \n"
"do_assume_context: \n"
" movl 4(%esp), %ebx \n"
" movl 8(%esp), %esi \n"
// We're going to call Processor::init_context, so just make sure
// we have enough stack space so we don't stomp over it
" subl $(" __STRINGIFY(4 + REGISTER_STATE_SIZE + TRAP_FRAME_SIZE + 4) "), %esp \n"
" pushl %esi \n"
" pushl %ebx \n"
" cld \n"
" call do_init_context \n"
" addl $4, %esp \n"
" addl $8, %esp \n"
" movl %eax, %esp \n" // move stack pointer to what Processor::init_context set up for us
" pushl %ebx \n" // push to_thread
" pushl %ebx \n" // push from_thread
@ -1143,9 +1167,13 @@ asm(
" jmp enter_thread_context \n"
);
void Processor::assume_context(Thread& thread)
void Processor::assume_context(Thread& thread, u32 flags)
{
do_assume_context(&thread);
#ifdef CONTEXT_SWITCH_DEBUG
dbg() << "Assume context for thread " << VirtualAddress(&thread) << " " << thread;
#endif
ASSERT_INTERRUPTS_DISABLED();
do_assume_context(&thread, flags);
ASSERT_NOT_REACHED();
}
@ -1161,6 +1189,7 @@ void Processor::initialize_context_switching(Thread& initial_thread)
m_tss.cs = m_tss.ds = m_tss.es = m_tss.gs = m_tss.ss = GDT_SELECTOR_CODE0 | 3;
m_tss.fs = GDT_SELECTOR_PROC | 3;
m_scheduler_initialized = true;
asm volatile(
"movl %[new_esp], %%esp \n" // swich to new stack
@ -1197,7 +1226,15 @@ void Processor::exit_trap(TrapFrame& trap)
ASSERT(m_in_irq >= trap.prev_irq_level);
m_in_irq = trap.prev_irq_level;
if (m_invoke_scheduler_async && !m_in_irq) {
if (!m_in_irq && !m_in_critical)
check_invoke_scheduler();
}
void Processor::check_invoke_scheduler()
{
ASSERT(!m_in_irq);
ASSERT(!m_in_critical);
if (m_invoke_scheduler_async && m_scheduler_initialized) {
m_invoke_scheduler_async = false;
Scheduler::invoke_async();
}