From: Matthias Kruk <m@m10k.eu>
Date: Tue, 1 Oct 2019 12:53:28 +0000 (+0900)
Subject: Issue the EOI at the beginning of the interrupt handler in order to avoid deadlocks
X-Git-Url: https://git.corax.cc/?a=commitdiff_plain;h=e2409a0e5269fb6ba5268d820b7ad50a0392ade1;p=corax

Issue the EOI at the beginning of the interrupt handler in order to avoid deadlocks
---

diff --git a/kernel/arch/interrupt.c b/kernel/arch/interrupt.c
index 8649a4a..b0db93c 100644
--- a/kernel/arch/interrupt.c
+++ b/kernel/arch/interrupt.c
@@ -50,6 +50,27 @@ int _int_handle(stack_frame_t ctx)
 	default:
 		break;
     }
+
+	/*
+	 * Issue the EOI before invoking the scheduler since it might reschedule
+	 * tasks, and the remainder of the function would not be executed until
+	 * this task gets scheduled again. Since the interrupt controller (whether
+	 * it be the i8259 or the APIC) will not issue further interrupts until
+	 * an EOI is issued, the next task would effectively not get preempted
+	 * until it makes a syscall or causes an exception (or an NMI or IPI
+	 * occurs).
+	 *
+	 * TLDR: Issue the EOI first to avoid deadlocks.
+	 */
+
+#if CONFIG_APIC == 1
+    /* FIXME: Make sure this is NOT done for NMI, SMI, INIT, ExtInt,
+     * SIPI or INIT-deassert mode interrupts */
+    _apic_eoi(ctx.intn);
+#else
+    _i8259_eoi(ctx.intn);
+#endif /* CONFIG_APIC */
+
 /*
     if(ctx.intn == 32) {
         unsigned *apic_esr;
@@ -95,14 +116,6 @@ int _int_handle(stack_frame_t ctx)
 		break;
 	}
 
-    #if CONFIG_APIC == 1
-    /* FIXME: Make sure this is NOT done for NMI, SMI, INIT, ExtInt,
-     * SIPI or INIT-deassert mode interrupts */
-    _apic_eoi(ctx.intn);
-    #else
-    _i8259_eoi(ctx.intn);
-    #endif /* CONFIG_APIC */
-
     return(0);
 }