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Kernel: Stop swallowing thread unblocks while process is stopped

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This easily led to kernel deadlocks if the stopped thread held an
important global mutex (like the disk cache lock) while blocking.
Resolve this by ensuring stopped threads have a chance to return to the
userland boundary before actually stopping.
This commit is contained in:
Idan Horowitz 2024-02-09 21:13:41 +02:00 committed by Andreas Kling
parent 458e990b7b
commit e38ccebfc8
Notes: sideshowbarker 2024-07-16 23:54:15 +09:00 
Author: https://github.com/IdanHo
Commit: https://github.com/SerenityOS/serenity/commit/e38ccebfc8
Pull-request: https://github.com/SerenityOS/serenity/pull/23142
4 changed files with 24 additions and 23 deletions
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4
Kernel/Syscalls/SyscallHandler.cpp
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@ -129,7 +129,7 @@ NEVER_INLINE void syscall_handler(TrapFrame* trap)
process.tracer_trap(*current_thread, regs); // this triggers SIGTRAP and stops the thread!
}
current_thread->yield_if_stopped();
current_thread->yield_if_should_be_stopped();
#if ARCH(X86_64)
// Apply a random offset in the range 0-255 to the stack pointer,
@ -178,7 +178,7 @@ NEVER_INLINE void syscall_handler(TrapFrame* trap)
process.tracer_trap(*current_thread, regs); // this triggers SIGTRAP and stops the thread!
}
current_thread->yield_if_stopped();
current_thread->yield_if_should_be_stopped();
current_thread->check_dispatch_pending_signal();

11
Kernel/Tasks/Scheduler.cpp
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@ -268,9 +268,14 @@ void Scheduler::context_switch(Thread* thread)
return;
// If the last process hasn't blocked (still marked as running),
// mark it as runnable for the next round.
if (from_thread->state() == Thread::State::Running)
from_thread->set_state(Thread::State::Runnable);
// mark it as runnable for the next round, unless it's supposed
// to be stopped, in which case just mark it as such.
if (from_thread->state() == Thread::State::Running) {
if (from_thread->should_be_stopped())
from_thread->set_state(Thread::State::Stopped);
else
from_thread->set_state(Thread::State::Runnable);
}
#ifdef LOG_EVERY_CONTEXT_SWITCH
auto const msg = "Scheduler[{}]: {} -> {} [prio={}] {:p}";

14
Kernel/Tasks/Thread.cpp
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@ -314,8 +314,8 @@ void Thread::unblock_from_blocker(Blocker& blocker)
SpinlockLocker block_lock(m_block_lock);
if (m_blocker != &blocker)
return;
if (!should_be_stopped() && !is_stopped())
unblock();
VERIFY(!is_stopped());
unblock();
};
if (Processor::current_in_irq() != 0) {
Processor::deferred_call_queue([do_unblock = move(do_unblock), self = try_make_weak_ptr().release_value_but_fixme_should_propagate_errors()]() {
@ -1273,14 +1273,8 @@ void Thread::set_state(State new_state, u8 stop_signal)
m_stop_state = previous_state != Thread::State::Running ? previous_state : Thread::State::Runnable;
auto& process = this->process();
if (!process.set_stopped(true)) {
process.for_each_thread([&](auto& thread) {
if (&thread == this)
return;
if (thread.is_stopped())
return;
dbgln_if(THREAD_DEBUG, "Stopping peer thread {}", thread);
thread.set_state(Thread::State::Stopped, stop_signal);
});
// Note that we don't explicitly stop peer threads, we let them stop on their own the next time they
// enter/exit a syscall, or once their current time slice runs out.
process.unblock_waiters(Thread::WaitBlocker::UnblockFlags::Stopped, stop_signal);
// Tell the parent process (if any) about this change.
if (auto parent = Process::from_pid_ignoring_jails(process.ppid())) {

18
Kernel/Tasks/Thread.h
View File

@ -32,6 +32,7 @@
#include <Kernel/Locking/LockRank.h>
#include <Kernel/Locking/SpinlockProtected.h>
#include <Kernel/Memory/VirtualRange.h>
#include <Kernel/Tasks/Scheduler.h>
#include <Kernel/UnixTypes.h>
namespace Kernel {
@ -789,16 +790,17 @@ public:
VirtualAddress thread_specific_data() const { return m_thread_specific_data; }
ALWAYS_INLINE void yield_if_stopped()
ALWAYS_INLINE void yield_if_should_be_stopped()
{
// If some thread stopped us, we need to yield to someone else
// We check this when entering/exiting a system call. A thread
// may continue to execute in user land until the next timer
// tick or entering the next system call, or if it's in kernel
// mode then we will intercept prior to returning back to user
// mode.
// A thread may continue to execute in user land until the next timer
// tick or until entering the next system call/exiting the current one.
if (!is_stopped() && should_be_stopped()) {
SpinlockLocker scheduler_lock(g_scheduler_lock);
set_state(State::Stopped);
}
// If we're stopped, we need to yield to someone else.
SpinlockLocker lock(m_lock);
while (state() == Thread::State::Stopped) {
while (is_stopped()) {
lock.unlock();
// We shouldn't be holding the big lock here
yield_without_releasing_big_lock();