riscv: add a return value to riscv_swint

arch/risc-v/src/common/riscv_fork.c

@@ -108,11 +108,16 @@ pid_t riscv_fork(const struct fork_s *context)
   uintptr_t newtop;
   uintptr_t stacktop;
   uintptr_t stackutil;
+  irqstate_t flags;
 #ifdef CONFIG_SCHED_THREAD_LOCAL
   uintptr_t tp;
 #endif
   UNUSED(context);
 
+  /* parent regs may change in irq, we should disable irq here */
+
+  flags = up_irq_save();
+
   /* Allocate and initialize a TCB for the child task. */
 
   child = nxtask_setup_fork((start_t)parent->xcp.regs[REG_RA]);
@@ -164,6 +169,8 @@ pid_t riscv_fork(const struct fork_s *context)
   child->cmn.xcp.regs[REG_TP] = tp;
 #endif
 
+  up_irq_restore(flags);
+
   /* And, finally, start the child task.  On a failure, nxtask_start_fork()
    * will discard the TCB by calling nxtask_abort_fork().
    */

arch/risc-v/src/common/riscv_internal.h

@@ -109,6 +109,10 @@
 #define PMP_ACCESS_DENIED   (-1)    /* Access set and denied */
 #define PMP_ACCESS_FULL     (1)     /* Access set and allowed */
 
+/* Return values from riscv_swint */
+
+#define SWINT_CONTEXT_SWITCH (1)    /* Indicate we need context switch */
+
 #ifndef __ASSEMBLY__
 
 /* Use ASM as rv64ilp32 compiler generated address is limited */

arch/risc-v/src/common/riscv_swint.c

@@ -496,6 +496,7 @@ int riscv_swint(int irq, void *context, void *arg)
   if (regs != new_regs)
     {
       restore_critical_section(this_task(), this_cpu());
+      return SWINT_CONTEXT_SWITCH;
     }
 
   return OK;

arch/risc-v/src/common/supervisor/riscv_perform_syscall.c

@@ -39,17 +39,17 @@ void *riscv_perform_syscall(uintreg_t *regs)
 {
   struct tcb_s *tcb;
   int cpu;
+  int ret;
 
   /* Set up the interrupt register set needed by swint() */
 
   up_set_current_regs(regs);
 
   /* Run the system call handler (swint) */
 
-  riscv_swint(0, regs, NULL);
-  tcb = this_task();
+  ret = riscv_swint(0, regs, NULL);
 
-  if (regs != tcb->xcp.regs)
+  if (ret == SWINT_CONTEXT_SWITCH)
     {
 #ifdef CONFIG_ARCH_ADDRENV
       /* Make sure that the address environment for the previously
@@ -69,10 +69,6 @@ void *riscv_perform_syscall(uintreg_t *regs)
       tcb = current_task(cpu);
       g_running_tasks[cpu] = tcb;
 
-      /* Restore the cpu lock */
-
-      restore_critical_section(tcb, cpu);
-
       /* If a context switch occurred while processing the interrupt then
        * current_regs may have change value.  If we return any value
        * different from the input regs, then the lower level will know