From cf58ad369e0701643f6cbfb1d9a8210dc99988e4 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Lo=C3=AFc=20Gr=C3=A9goire?= <loic@gregoire.dev>
Date: Wed, 2 Sep 2026 22:17:54 -0400
Subject: [PATCH] ke: freeze CPUs on panic

---
 src/kern/amd64/impl.zig |  4 ++++
 src/kern/ipi.zig        | 39 ++++++++++++++++++++++++++++++++++++++-
 src/kern/panic.zig      | 36 +++++++++++++++++++++++++++++++-----
 src/kern/private.zig    |  3 +++
 4 files changed, 76 insertions(+), 6 deletions(-)

diff --git a/src/kern/amd64/impl.zig b/src/kern/amd64/impl.zig
index 302d3b4..159a333 100644
--- a/src/kern/amd64/impl.zig
+++ b/src/kern/amd64/impl.zig
@@ -158,6 +158,10 @@ pub inline fn percpu_ptr_other(variable: anytype, id: u32) @TypeOf(variable) {
     return percpu_ptr_for(variable, id);
 }
 
+pub inline fn halt() void {
+    asm volatile ("hlt");
+}
+
 pub inline fn percpu_ptr(variable: anytype) @TypeOf(variable) {
     const offset = asm volatile ("mov %%gs:(%[self]), %[out]"
         : [out] "=r" (-> u64),
diff --git a/src/kern/ipi.zig b/src/kern/ipi.zig
index 97b8b70..285b947 100644
--- a/src/kern/ipi.zig
+++ b/src/kern/ipi.zig
@@ -4,7 +4,7 @@ const r = @import("root");
 const std = @import("std");
 
 const ke = r.ke;
-const ki = r.ki;
+const ki = ke.private;
 const pl = r.pl;
 
 const State = enum(u8) {
@@ -31,6 +31,8 @@ const PerCpu = struct {
 
 const percpu = ke.CpuLocal(PerCpu, undefined);
 
+var frozen_cpus: std.atomic.Value(u32) = .init(0);
+
 /// Call a function on another CPU.
 /// The function will be executed synchronously, i.e this will block until
 /// the function finishes running. The callback is called with the sender cpu
@@ -63,6 +65,10 @@ pub fn unicast(
     ke.ipl.lower(ipl);
 }
 
+/// Call a function on all other CPUs.
+/// The function will be executed synchronously, i.e this will block until
+/// the function finishes running. The callback is called with the sender cpu
+/// and provided argument as arguments.
 pub fn broadcast(func: *const fn (u32, ?*anyopaque) void, arg: ?*anyopaque) void {
     const ipl = ke.ipl.raise(.Dispatch);
     const curcpu = percpu.local();
@@ -91,6 +97,28 @@ pub fn broadcast(func: *const fn (u32, ?*anyopaque) void, arg: ?*anyopaque) void
     ke.ipl.lower(ipl);
 }
 
+/// Freeze all other CPUs.
+/// Called at IPL >= Dispatch.
+pub fn freeze_cpus() void {
+    frozen_cpus.store(1, .monotonic);
+
+    for (0..ke.ncpus) |i| {
+        if (i == ke.cpu.current()) continue;
+        const remote = percpu.remote(@intCast(i));
+        remote.pending.set(ke.cpu.current(), .monotonic);
+
+        const state = remote.state.swap(.Pending, .release);
+
+        if (state == .Idle) {
+            pl.send_ipi(@intCast(i));
+        }
+    }
+
+    while (frozen_cpus.load(.monotonic) != ke.ncpus) {
+        std.atomic.spinLoopHint();
+    }
+}
+
 pub fn ipi_handler() void {
     const curcpu = percpu.local();
 
@@ -105,6 +133,15 @@ pub fn ipi_handler() void {
             .monotonic,
         );
 
+        if (frozen_cpus.load(.monotonic) != 0) {
+            // We have been requested to freeze, ack and do it now.
+            _ = frozen_cpus.fetchAdd(1, .monotonic);
+
+            while (true) {
+                ki.impl.halt();
+            }
+        }
+
         if (val != null) {
             // CAS failed.
             return;
diff --git a/src/kern/panic.zig b/src/kern/panic.zig
index b26526d..2c3c6db 100644
--- a/src/kern/panic.zig
+++ b/src/kern/panic.zig
@@ -71,24 +71,50 @@ fn walk_stack_frame(base: usize) void {
 }
 
 pub var panic_lock: ke.SpinLock = .init();
+var crash_count: std.atomic.Value(u8) = .init(0);
 
 pub fn panic_with_frame(
     msg: []const u8,
     frame: usize,
 ) noreturn {
-    std.log.err("KERNEL PANIC: {s} on CPU {}, curthread is {*}", .{ msg, ke.cpu.current(), ki.sched.percpu.local().current_thread.? });
+    _ = ki.impl.disable_interrupts();
+
+    std.log.info("Crash count is {} on cpu {}", .{ crash_count.load(.monotonic), ke.cpu.current() });
+
+    if (crash_count.fetchAdd(1, .monotonic) != 0) {
+        std.log.err("Recursive panic from CPU {}", .{ke.cpu.current()});
+        // Another CPU has already crashed, just freeze manually right now.
+
+        while (true) {
+            ki.impl.halt();
+        }
+    }
+
+    // We're the first one who actually crashed, that means we get to handle
+    // things like dumping the system info and freezing other CPUs. Start by
+    // doing the freeze.
+    ki.ipi.freeze_cpus();
+
+    _ = ke.ipl.raise(.High);
+
+    std.log.err("KERNEL PANIC: {s} on CPU {}, curthread is {*}", .{
+        msg,
+        ke.cpu.current(),
+        ki.sched.percpu.local().current_thread.?,
+    });
+
     std.log.err("Stack trace:", .{});
+
     walk_stack_frame(frame);
 
-    panic_lock.release_no_ipl();
-
-    while (true) {}
+    while (true) {
+        ki.impl.halt();
+    }
 }
 
 pub fn panic(
     msg: []const u8,
     _: ?usize,
 ) noreturn {
-    panic_lock.acquire_no_ipl();
     panic_with_frame(msg, @frameAddress());
 }
diff --git a/src/kern/private.zig b/src/kern/private.zig
index c53f672..bb33425 100644
--- a/src/kern/private.zig
+++ b/src/kern/private.zig
@@ -46,6 +46,9 @@ const ImplSchema = struct {
         return false;
     }
 
+    /// Halt the CPU. This is called on crashes.
+    pub fn halt() void {}
+
     /// Restore the state of interrupts.
     pub fn restore_interrupts(state: bool) void {
         _ = state;