From e698cfdfd16bae08cb33c73bb575c89ec8c062ba Mon Sep 17 00:00:00 2001
From: Benji Dial <benji@benjidial.net>
Date: Sun, 28 Dec 2025 20:27:00 -0500
Subject: [PATCH] kernel: fix race condition in input component

---
 src/kernel/input.c       |  7 +++++--
 src/kernel/input.h       |  1 +
 src/kernel/scheduler.asm | 18 ++++++++++++++++++
 src/kernel/scheduler.h   |  3 +++
 4 files changed, 27 insertions(+), 2 deletions(-)

diff --git a/src/kernel/input.c b/src/kernel/input.c
index 4c24293..0913696 100644
--- a/src/kernel/input.c
+++ b/src/kernel/input.c
@@ -38,6 +38,7 @@ void add_mouse_movement(int x, int y) {
     add_to_queue(&ready_continuations, &waiting_continuation);
     total_unreported_x_movement = 0;
     total_unreported_y_movement = 0;
+    is_somebody_waiting_for_mouse_packet = 0;
   }
 
 }
@@ -46,6 +47,8 @@ void syscall_wait_for_mouse_packet(struct mouse_packet *packet_out) {
 
   assert(running_thread != 0);
 
+  __asm__ ("cli");
+
   //TODO: handle these
   if (is_somebody_waiting_for_mouse_packet ||
       !is_mapped_writable(
@@ -57,12 +60,12 @@ void syscall_wait_for_mouse_packet(struct mouse_packet *packet_out) {
     packet_out->y_change = total_unreported_y_movement;
     total_unreported_x_movement = 0;
     total_unreported_y_movement = 0;
+    __asm__ ("sti");
     return;
   }
 
   is_somebody_waiting_for_mouse_packet = 1;
   resume_by_reporting_to = packet_out;
-  yield(&waiting_continuation);
-  is_somebody_waiting_for_mouse_packet = 0;
+  yield_sti(&waiting_continuation);
 
 }
diff --git a/src/kernel/input.h b/src/kernel/input.h
index bb5970b..65059b0 100644
--- a/src/kernel/input.h
+++ b/src/kernel/input.h
@@ -19,6 +19,7 @@
 
 #include <kernel-public/input.h>
 
+//should only be called with interrupts disabled
 void add_mouse_movement(int x, int y);
 
 void syscall_wait_for_mouse_packet(struct mouse_packet *packet_out);
diff --git a/src/kernel/scheduler.asm b/src/kernel/scheduler.asm
index aefc835..76b16f6 100644
--- a/src/kernel/scheduler.asm
+++ b/src/kernel/scheduler.asm
@@ -53,3 +53,21 @@ yield:
 
 .ret:
   ret
+
+global yield_sti
+yield_sti:
+  mov qword [rdi], ret
+  mov qword [rdi + 8], rbx
+  mov qword [rdi + 16], rbp
+  mov qword [rdi + 24], rsp
+  mov qword [rdi + 32], r12
+  mov qword [rdi + 40], r13
+  mov qword [rdi + 48], r14
+  mov qword [rdi + 56], r15
+
+  sti
+
+  jmp resume_next_continuation
+
+.ret:
+  ret
diff --git a/src/kernel/scheduler.h b/src/kernel/scheduler.h
index cac8936..febefd2 100644
--- a/src/kernel/scheduler.h
+++ b/src/kernel/scheduler.h
@@ -54,3 +54,6 @@ int take_from_queue(struct continuation_queue *queue, struct continuation_info *
 //saves a continuation that returns from this function to save_current_continuation_to, then resumes
 //the next ready continuation (thus doesn't return until save_current_continuation_to is resumed).
 void yield(struct continuation_info *save_current_continuation_to);
+
+//save as yield but enables interrupts between saving this continuation and resuming next ready one.
+void yield_sti(struct continuation_info *save_current_continuation_to);