riscv: use g_running_task store current regs

This commit fixes the regression from https://github.com/apache/nuttx/pull/13561

In order to determine whether a context switch has occurred,
we can use g_running_task to store the current regs.
This allows us to compare the current register state with the previously
stored state to identify if a context switch has taken place.

Signed-off-by: hujun5 <hujun5@xiaomi.com>

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

@@ -58,6 +58,7 @@
 
 uintreg_t *riscv_doirq(int irq, uintreg_t *regs)
 {
+  struct tcb_s **running_task = &g_running_tasks[this_cpu()];
   struct tcb_s *tcb = this_task();
 
   board_autoled_on(LED_INIRQ);
@@ -71,9 +72,10 @@ uintreg_t *riscv_doirq(int irq, uintreg_t *regs)
     {
       regs[REG_EPC] += 4;
     }
-  else
+
+  if (*running_task != NULL)
     {
-      tcb->xcp.regs = regs;
+      (*running_task)->xcp.regs = regs;
     }
 
   /* Current regs non-zero indicates that we are processing an interrupt;
@@ -97,7 +99,7 @@ uintreg_t *riscv_doirq(int irq, uintreg_t *regs)
    * returning from the interrupt.
    */
 
-  if (regs != tcb->xcp.regs)
+  if ((*running_task) != tcb)
     {
 #ifdef CONFIG_ARCH_ADDRENV
       /* Make sure that the address environment for the previously
@@ -119,15 +121,7 @@ uintreg_t *riscv_doirq(int irq, uintreg_t *regs)
        * crashes.
        */
 
-      g_running_tasks[this_cpu()] = tcb;
-
-      /* 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
-       * that a context switch occurred during interrupt processing.
-       */
-
-      regs = tcb->xcp.regs;
+      *running_task = tcb;
     }
 
   /* Set current_regs to NULL to indicate that we are no longer in an
@@ -138,5 +132,5 @@ uintreg_t *riscv_doirq(int irq, uintreg_t *regs)
 
 #endif
   board_autoled_off(LED_INIRQ);
-  return regs;
+  return tcb->xcp.regs;
 }

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

@@ -78,6 +78,10 @@ void up_exit(int status)
 
   nxsched_resume_scheduler(tcb);
 
+  /* g_running_tasks is not valid now */
+
+  g_running_tasks[this_cpu()] = NULL;
+
   /* Then switch contexts */
 
   riscv_fullcontextrestore(tcb);

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

@@ -109,10 +109,6 @@
 #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_sigdeliver.c

@@ -162,6 +162,10 @@ retry:
   rtcb->irqcount--;
 #endif
 
+  /* g_running_tasks is not valid now */
+
+  g_running_tasks[this_cpu()] = NULL;
+
   rtcb->xcp.regs = regs;
   riscv_fullcontextrestore(rtcb);
 }

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

@@ -257,7 +257,6 @@ int riscv_swint(int irq, void *context, void *arg)
           struct tcb_s *next = (struct tcb_s *)(uintptr_t)regs[REG_A2];
 
           DEBUGASSERT(regs[REG_A1] != 0 && regs[REG_A2] != 0);
-          prev->xcp.regs = regs;
           riscv_savecontext(prev);
           new_regs = next->xcp.regs;
           riscv_restorecontext(next);
@@ -496,7 +495,6 @@ 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

@@ -37,9 +37,13 @@
 
 void *riscv_perform_syscall(uintreg_t *regs)
 {
+  struct tcb_s **running_task = &g_running_tasks[this_cpu()];
   struct tcb_s *tcb;
-  int cpu;
-  int ret;
+
+  if (*running_task != NULL)
+    {
+      (*running_task)->xcp.regs = regs;
+    }
 
   /* Set up the interrupt register set needed by swint() */
 
@@ -47,9 +51,10 @@ void *riscv_perform_syscall(uintreg_t *regs)
 
   /* Run the system call handler (swint) */
 
-  ret = riscv_swint(0, regs, NULL);
+  riscv_swint(0, regs, NULL);
+  tcb = this_task();
 
-  if (ret == SWINT_CONTEXT_SWITCH)
+  if ((*running_task) != tcb)
     {
 #ifdef CONFIG_ARCH_ADDRENV
       /* Make sure that the address environment for the previously
@@ -65,20 +70,10 @@ void *riscv_perform_syscall(uintreg_t *regs)
        * assertion logic for reporting crashes.
        */
 
-      cpu = this_cpu();
-      tcb = current_task(cpu);
-      g_running_tasks[cpu] = tcb;
-
-      /* 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
-       * that a context switch occurred during interrupt processing.
-       */
-
-      regs = tcb->xcp.regs;
+      *running_task = tcb;
     }
 
   up_set_current_regs(NULL);
 
-  return regs;
+  return tcb->xcp.regs;
 }