From 7002d2feab970aa740820d9c3a42891c6f53bb21 Mon Sep 17 00:00:00 2001
From: August <shibedrill1@gmail.com>
Date: Thu, 6 Nov 2025 01:34:24 -0500
Subject: [PATCH] Investigate talc dealloc panic deadlock

---
 Cargo.lock                       | 25 ++++++++++++-------------
 src/kernel/arch/x86_64/paging.rs | 24 +++++++++++++++++++++---
 src/kernel/main.rs               |  2 ++
 src/kernel/panic.rs              |  2 +-
 4 files changed, 36 insertions(+), 17 deletions(-)

diff --git a/Cargo.lock b/Cargo.lock
index 6afea4f..bd6e914 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -45,9 +45,9 @@ checksum = "1e4b40c7323adcfc0a41c4b88143ed58346ff65a288fc144329c5c45e05d70c6"
 
 [[package]]
 name = "bitflags"
-version = "2.9.4"
+version = "2.10.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "2261d10cca569e4643e526d8dc2e62e433cc8aba21ab764233731f8d369bf394"
+checksum = "812e12b5285cc515a9c72a5c1d3b6d46a19dac5acfef5265968c166106e31dd3"
 
 [[package]]
 name = "build_const"
@@ -177,11 +177,10 @@ dependencies = [
 
 [[package]]
 name = "lock_api"
-version = "0.4.13"
+version = "0.4.14"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "96936507f153605bddfcda068dd804796c84324ed2510809e5b2a624c81da765"
+checksum = "224399e74b87b5f3557511d98dff8b14089b3dadafcab6bb93eab67d3aace965"
 dependencies = [
- "autocfg",
  "scopeguard",
 ]
 
@@ -255,18 +254,18 @@ checksum = "f84267b20a16ea918e43c6a88433c2d54fa145c92a811b5b047ccbe153674483"
 
 [[package]]
 name = "proc-macro2"
-version = "1.0.101"
+version = "1.0.103"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "89ae43fd86e4158d6db51ad8e2b80f313af9cc74f5c0e03ccb87de09998732de"
+checksum = "5ee95bc4ef87b8d5ba32e8b7714ccc834865276eab0aed5c9958d00ec45f49e8"
 dependencies = [
  "unicode-ident",
 ]
 
 [[package]]
 name = "quote"
-version = "1.0.40"
+version = "1.0.41"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "1885c039570dc00dcb4ff087a89e185fd56bae234ddc7f056a945bf36467248d"
+checksum = "ce25767e7b499d1b604768e7cde645d14cc8584231ea6b295e9c9eb22c02e1d1"
 dependencies = [
  "proc-macro2",
 ]
@@ -330,9 +329,9 @@ checksum = "5cdeee85371b1ec1f4b305c91787271a39f56b66e673bdbd73b7742150de5b0e"
 
 [[package]]
 name = "syn"
-version = "2.0.106"
+version = "2.0.109"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "ede7c438028d4436d71104916910f5bb611972c5cfd7f89b8300a8186e6fada6"
+checksum = "2f17c7e013e88258aa9543dcbe81aca68a667a9ac37cd69c9fbc07858bfe0e2f"
 dependencies = [
  "proc-macro2",
  "quote",
@@ -361,9 +360,9 @@ dependencies = [
 
 [[package]]
 name = "unicode-ident"
-version = "1.0.19"
+version = "1.0.22"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "f63a545481291138910575129486daeaf8ac54aee4387fe7906919f7830c7d9d"
+checksum = "9312f7c4f6ff9069b165498234ce8be658059c6728633667c526e27dc2cf1df5"
 
 [[package]]
 name = "volatile"
diff --git a/src/kernel/arch/x86_64/paging.rs b/src/kernel/arch/x86_64/paging.rs
index 1c49e82..90c8607 100644
--- a/src/kernel/arch/x86_64/paging.rs
+++ b/src/kernel/arch/x86_64/paging.rs
@@ -5,13 +5,20 @@
 
 use crate::constants::KERNEL_BUILD_PROFILE;
 use crate::{LOGGER, LogLevel, format, log_info, log_trace, memory::HHDM_RESPONSE};
+use crate::memory::alloc::boxed::Box;
 use free_list::{PAGE_SIZE, PageLayout};
+use lazy_static::lazy_static;
+use spin::Mutex;
 use x86_64::{
     PhysAddr, VirtAddr,
     registers::control::*,
     structures::paging::{PageTable, PageTableFlags},
 };
 
+lazy_static! {
+    pub static ref KERNEL_PML4: Mutex<Option<Box<PageTable>>> = Mutex::new(None);
+}
+
 pub fn switch_ptable() {
     let allocated_region = crate::memory::FREELIST
         .lock()
@@ -20,9 +27,20 @@ pub fn switch_ptable() {
     log_info!("Got region for new PML4: 0x{:x}", allocated_region.start());
     let pml4_start_vaddr = allocated_region.start() + HHDM_RESPONSE.offset() as usize;
     let pml4_ptr = pml4_start_vaddr as *mut PageTable;
-    let mut pml4 = unsafe { crate::memory::alloc::boxed::Box::from_raw(pml4_ptr) };
-    *pml4 = PageTable::new();
-    log_info!("Initialized page table at 0x{:p}", pml4);
+
+    /*
+    Dropping this PML4 causes a deadlock. Here is why:
+    - The allocator, Talc, did not allocate the memory we built the PML4 in.
+    - When this function exits, the allocator is *locked*.
+    - The allocator is told to drop this PML4, and panics, because it was never "allocated" to begin with.
+    - The allocator panics.
+    - The panic function tries to call the logging code.
+    - The logging code tries to acquire lock on the allocator, but it will never get it, since it is locked
+      until the function finishes exiting. Which it won't, because the allocator panicked.
+    */
+    //let mut pml4 = unsafe { crate::memory::alloc::boxed::Box::from_raw(pml4_ptr) };
+    //*pml4 = PageTable::new();
+    //log_info!("Initialized page table at 0x{:p}", pml4);
 }
 
 pub fn get_mappings() {
diff --git a/src/kernel/main.rs b/src/kernel/main.rs
index 32a7cf7..4075981 100644
--- a/src/kernel/main.rs
+++ b/src/kernel/main.rs
@@ -4,6 +4,7 @@
 #![no_std]
 #![no_main]
 #![feature(abi_x86_interrupt)]
+#![feature(breakpoint)]
 
 mod arch;
 mod boot;
@@ -160,6 +161,7 @@ unsafe extern "C" fn main() -> ! {
     log_info!("Virtualization provider: {:?}", virt_supported());
 
     arch::x86_64::paging::switch_ptable();
+    log_info!("Made it this far");
 
     panic!("Finished boot, but cannot start init because processes not implemented!");
 }
diff --git a/src/kernel/panic.rs b/src/kernel/panic.rs
index 4c773dc..dfa9f2d 100644
--- a/src/kernel/panic.rs
+++ b/src/kernel/panic.rs
@@ -3,8 +3,8 @@
 
 use core::panic::*;
 
-use crate::format;
 use crate::{LOGGER, LogLevel};
+use crate::format;
 
 #[panic_handler]
 pub fn panic(info: &PanicInfo) -> ! {