[arm] Ensure context switch doesn't happen from irq

arch/arch.c

@@ -1 +1,13 @@
-// empty file to help build empty arch module
+/*
+ * Copyright (c) 2020 Travis Geiselbrecht
+ *
+ * Use of this source code is governed by a MIT-style
+ * license that can be found in the LICENSE file or at
+ * https://opensource.org/licenses/MIT
+ */
+
+#include <arch/ops.h>
+
+__WEAK bool arch_in_int_handler(void) {
+    return false;
+}

arch/arm/arm/arch.c

@@ -47,6 +47,32 @@ static void arm_basic_setup(void);
 static void spinlock_test(void);
 static void spinlock_test_secondary(void);
 
+static uint32_t cpu_in_irq_ctxt[SMP_MAX_CPUS];
+
+enum handler_return arch_irq(struct arm_iframe *frame) {
+    enum handler_return ret;
+    uint32_t cpu = arch_curr_cpu_num();
+    DEBUG_ASSERT(cpu < SMP_MAX_CPUS);
+
+    cpu_in_irq_ctxt[cpu] = 1;
+    ret = platform_irq(frame);
+    cpu_in_irq_ctxt[cpu] = 0;
+    return ret;
+}
+
+bool arch_in_int_handler() {
+#if ARM_ISA_ARMV7M
+    uint32_t ipsr;
+    __asm volatile ("MRS %0, ipsr" : "=r" (ipsr) );
+    return (ipsr & IPSR_ISR_Msk);
+#else
+    uint32_t cpu = arch_curr_cpu_num();
+    DEBUG_ASSERT(cpu < SMP_MAX_CPUS);
+
+    return (cpu_in_irq_ctxt[cpu] == 1);
+#endif
+}
+
 #if WITH_SMP
 /* smp boot lock */
 spin_lock_t arm_boot_cpu_lock = 1;

arch/arm/arm/exceptions.S

@@ -204,18 +204,8 @@ FUNCTION(arm_irq)
 
     /* r0 now holds pointer to iframe */
 
-    /* track that we're inside an irq handler */
-    LOADCONST(r2, __arm_in_handler)
-    mov     r1, #1
-    str     r1, [r2]
-
     /* call into higher level code */
-    bl  platform_irq
-
-    /* clear the irq handler status */
-    LOADCONST(r1, __arm_in_handler)
-    mov     r2, #0
-    str     r2, [r1]
+    bl arch_irq
 
     /* reschedule if the handler returns nonzero */
     cmp     r0, #0
@@ -237,7 +227,3 @@ FUNCTION(arm_fiq)
 DATA(__irq_cycle_count)
     .word   0
 #endif
-
-.data
-DATA(__arm_in_handler)
-    .word   0

arch/arm/include/arch/arch_ops.h

@@ -20,6 +20,8 @@
 
 __BEGIN_CDECLS
 
+enum handler_return platform_irq(struct arm_iframe *frame);
+
 #if ARM_ISA_ARMV7 || (ARM_ISA_ARMV6 && !__thumb__)
 #define ENABLE_CYCLE_COUNTER 1
 
@@ -67,19 +69,6 @@ static inline bool arch_fiqs_disabled(void) {
     return !!state;
 }
 
-static inline bool arch_in_int_handler(void) {
-#if ARM_ISA_ARMV7M
-    uint32_t ipsr;
-    __asm volatile ("MRS %0, ipsr" : "=r" (ipsr) );
-    return (ipsr & IPSR_ISR_Msk);
-#else
-    /* set by the interrupt glue to track that the cpu is inside a handler */
-    extern bool __arm_in_handler;
-
-    return __arm_in_handler;
-#endif
-}
-
 static inline ulong arch_cycle_count(void) {
 #if ARM_ISA_ARMV7M
 #if ENABLE_CYCLE_COUNTER

arch/arm64/arch.c

@@ -26,6 +26,25 @@
 static spin_lock_t arm_boot_cpu_lock = 1;
 static volatile int secondaries_to_init = 0;
 #endif
+static uint32_t cpu_in_irq_ctxt[SMP_MAX_CPUS];
+
+enum handler_return arch_irq(struct arm64_iframe_short *frame) {
+    enum handler_return ret;
+    uint32_t cpu = arch_curr_cpu_num();
+    DEBUG_ASSERT(cpu < SMP_MAX_CPUS);
+
+    cpu_in_irq_ctxt[cpu] = 1;
+    ret = platform_irq(frame);
+    cpu_in_irq_ctxt[cpu] = 0;
+    return ret;
+}
+
+bool arch_in_int_handler() {
+    uint32_t cpu = arch_curr_cpu_num();
+    DEBUG_ASSERT(cpu < SMP_MAX_CPUS);
+
+    return (cpu_in_irq_ctxt[cpu] == 1);
+}
 
 static void arm64_cpu_early_init(void) {
     /* set the vector base */

arch/arm64/exceptions.S

@@ -111,7 +111,7 @@ add sp, sp, #32
     regsave_short
     msr daifclr, #1 /* reenable fiqs once elr and spsr have been saved */
     mov x0, sp
-    bl  platform_irq
+    bl  arch_irq
     cbz x0, .Lirq_exception_no_preempt\@
     bl  thread_preempt
 .Lirq_exception_no_preempt\@:

arch/arm64/include/arch/arch_ops.h

@@ -17,6 +17,7 @@
 #define ENABLE_CYCLE_COUNTER 1
 
 void arch_stacktrace(uint64_t fp, uint64_t pc);
+enum handler_return platform_irq(struct arm64_iframe_short *frame);
 
 // override of some routines
 static inline void arch_enable_ints(void) {

arch/include/arch/ops.h

@@ -16,11 +16,12 @@
 
 __BEGIN_CDECLS
 
+bool arch_in_int_handler(void);
+
 /* fast routines that most arches will implement inline */
 static void arch_enable_ints(void);
 static void arch_disable_ints(void);
 static bool arch_ints_disabled(void);
-static bool arch_in_int_handler(void);
 
 static ulong arch_cycle_count(void);
 

kernel/thread.c

@@ -472,6 +472,10 @@ void thread_resched(void) {
     thread_t *current_thread = get_current_thread();
     uint cpu = arch_curr_cpu_num();
 
+    /* Assert that cpu is not in active irq handling
+     * context */
+    ASSERT(!arch_in_int_handler());
+
     DEBUG_ASSERT(arch_ints_disabled());
     DEBUG_ASSERT(spin_lock_held(&thread_lock));
     DEBUG_ASSERT(current_thread->state != THREAD_RUNNING);