From 82175f342e1b64fcdf5e7d96319016fdbaf9b39a Mon Sep 17 00:00:00 2001
From: Mark Poliakov <mark@alnyan.me>
Date: Sat, 15 Feb 2025 20:18:30 +0200
Subject: [PATCH] debug: avoid debugging deadlocks

---
 kernel/driver/virtio/core/src/queue.rs |  5 ++---
 kernel/libk/src/debug/mod.rs           | 23 +++++++++++++++++++----
 2 files changed, 21 insertions(+), 7 deletions(-)

diff --git a/kernel/driver/virtio/core/src/queue.rs b/kernel/driver/virtio/core/src/queue.rs
index f3df3819..45ea0f25 100644
--- a/kernel/driver/virtio/core/src/queue.rs
+++ b/kernel/driver/virtio/core/src/queue.rs
@@ -1,13 +1,12 @@
 //! VirtIO queue implementation.
 
-use core::{future::poll_fn, mem::MaybeUninit, task::Poll, time::Duration};
+use core::{future::poll_fn, mem::MaybeUninit, task::Poll};
 
 use alloc::{boxed::Box, sync::Arc};
 use device_api::dma::DmaAllocator;
 use libk::{
     dma::{BusAddress, DmaBuffer, DmaSlice, DmaSliceMut},
     error::Error,
-    task::runtime::psleep,
 };
 use libk_util::{
     event::OneTimeEvent, hash_table::DefaultHashTable, sync::IrqSafeSpinlock, waker::QueueWaker,
@@ -451,7 +450,7 @@ impl VirtQueue<VqManualNotification> {
             if length != 0 {
                 break;
             }
-            psleep(Duration::from_millis(1));
+            core::hint::spin_loop();
         }
         Ok(length)
     }
diff --git a/kernel/libk/src/debug/mod.rs b/kernel/libk/src/debug/mod.rs
index 8c19dece..462c92d6 100644
--- a/kernel/libk/src/debug/mod.rs
+++ b/kernel/libk/src/debug/mod.rs
@@ -7,15 +7,16 @@ use alloc::{
 use core::{
     fmt,
     str::FromStr,
-    sync::atomic::{AtomicBool, Ordering},
+    sync::atomic::{AtomicBool, AtomicU32, Ordering},
 };
 use ring::RingLoggerSink;
 
-use libk_util::{sync::IrqSafeSpinlock, OneTimeInit};
+use libk_util::OneTimeInit;
 use sink::DEBUG_SINKS;
 use yggdrasil_abi::error::Error;
 
 use crate::{
+    arch::Cpu,
     fs::sysfs::{
         attribute::{StringAttribute, StringAttributeOps},
         object::KObject,
@@ -31,7 +32,7 @@ pub use panic::{panic_log, PanicLoggerSink};
 pub use ring::add_kernel_log_file;
 pub use sink::{add_early_sink, add_serial_sink, add_sink, disable_early_sinks, DebugSink};
 
-static DEBUG_LOCK: IrqSafeSpinlock<()> = IrqSafeSpinlock::new(());
+static DEBUG_LOCK: AtomicU32 = AtomicU32::new(u32::MAX);
 static MUTE_DEBUG: AtomicBool = AtomicBool::new(false);
 
 pub struct MuteGuard(bool);
@@ -104,6 +105,17 @@ impl From<log::Level> for LogLevel {
     }
 }
 
+fn lock_debug() -> bool {
+    let cpu = Cpu::try_local().map_or(0, |cpu| cpu.id());
+    loop {
+        match DEBUG_LOCK.compare_exchange(u32::MAX, cpu, Ordering::Acquire, Ordering::Relaxed) {
+            Ok(_) => return true,
+            Err(x) if x == cpu => return false,
+            _ => core::hint::spin_loop(),
+        }
+    }
+}
+
 impl log::Log for KernelLoggerSink {
     fn enabled(&self, metadata: &log::Metadata) -> bool {
         metadata.target() != "io"
@@ -120,12 +132,15 @@ impl log::Log for KernelLoggerSink {
 
         RingLoggerSink.log(record);
 
-        let _guard = DEBUG_LOCK.lock();
+        if !lock_debug() {
+            return;
+        }
         for sink in DEBUG_SINKS.read().iter() {
             if sink.enabled(record.metadata()) {
                 sink.log(record);
             }
         }
+        DEBUG_LOCK.store(u32::MAX, Ordering::Release);
     }
 
     fn flush(&self) {}