[incubator-nuttx] 01/06: arch: cxd56xx: Fix the pause handler for SMP

[ma...@apache.org]

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masayuki pushed a commit to branch releases/10.0
in repository https://gitbox.apache.org/repos/asf/incubator-nuttx.git

commit 31a8167821b0a82a384dfd0e4d3ef867e2a8184d
Author: Masayuki Ishikawa <ma...@gmail.com>
AuthorDate: Fri Nov 20 13:16:45 2020 +0900

    arch: cxd56xx: Fix the pause handler for SMP
    
    Summary:
    - I noticed that sched_add_readytorun() runs on multiple CPUs simultaneously
    - Finally, I found the root cause which was described in TODO
    - Actually, the task newly scheduled on remote CPU did not acquire g_cpu_irqlock
    - This commit fixes this issue by adding a critical section to the pause handler
    - Which will acquire g_cpu_irqlock on the remote CPU explicitly
    
    Impact:
    - SMP only
    
    Testing:
    - Tested with spresense:wifi_smp (NCPUS=2 and 4)
    - Run smp, ostest, nxplayer
    
    Signed-off-by: Masayuki Ishikawa <Ma...@jp.sony.com>
---
 arch/arm/src/cxd56xx/cxd56_cpupause.c | 16 ++++++++++++++--
 1 file changed, 14 insertions(+), 2 deletions(-)

diff --git a/arch/arm/src/cxd56xx/cxd56_cpupause.c b/arch/arm/src/cxd56xx/cxd56_cpupause.c
index c8bd410..1f5e6b4 100644
--- a/arch/arm/src/cxd56xx/cxd56_cpupause.c
+++ b/arch/arm/src/cxd56xx/cxd56_cpupause.c
@@ -283,6 +283,7 @@ int up_cpu_paused(int cpu)
 int arm_pause_handler(int irq, void *c, FAR void *arg)
 {
   int cpu = up_cpu_index();
+  int ret = OK;
 
   DPRINTF("cpu%d will be paused \n", cpu);
 
@@ -297,10 +298,21 @@ int arm_pause_handler(int irq, void *c, FAR void *arg)
 
   if (spin_islocked(&g_cpu_paused[cpu]))
     {
-      return up_cpu_paused(cpu);
+      /* NOTE: up_cpu_paused() needs to be executed in a critical section
+       * to ensure that this CPU holds g_cpu_irqlock. However, adding
+       * a critical section in up_cpu_paused() is not a good idea,
+       * because it is also called in enter_critical_section() to break
+       * a deadlock
+       */
+
+      irqstate_t flags = enter_critical_section();
+
+      ret = up_cpu_paused(cpu);
+
+      leave_critical_section(flags);
     }
 
-  return OK;
+  return ret;
 }
 
 /****************************************************************************