[Xen-devel] Bug report and patch about IRQ freezing after gic_restore_state

[Jaeyong Yoo <jaeyong.yoo@xxxxxxxxxxx>]

Hello xen, 

I'm running xen on Arndale board and if I run both iperf and du command at 
Dom0, 
one of IRQ (either SATA or network) suddenly stop occuring anymore. 
After some investigation, I found out that when context switching at Xen, 
IRQs in LR (about to be delivered to Doms) could be lost and never occur 
anymore. 
Here goes function call sequence that this problem occurs: 
(in context switching)
  - schedule_tail 
      - ctxt_switch_from 
      - local_irq_enable 
      - // after this part, some IRQ can occur and could be directly written to 
LR 
      - ctxt_switch_to 
          - ... (some more functions) 
          - // before the above IRQ is delivered to Dom (and maintenance IRQ 
not called),
            // gic_restore_state can be called 
          - gic_restore_state /* when restoring gic state, the above IRQ 
                                       * (written to LR) is overwritten 
                                       * to the previous values, and somehow, 
                                       * the corresponding IRQ never occur 
again */ 

I made the following patch (i.e., enable local irq after gic_restore_state) 
for preventing the above problem. 

Signed-off-by: Jaeyong Yoo <jaeyong.yoo@xxxxxxxxxxx> 
--- 
 xen/arch/arm/domain.c |    4 ++-- 
 xen/arch/arm/gic.c    |    4 ++-- 
 2 files changed, 4 insertions(+), 4 deletions(-) 
diff --git a/xen/arch/arm/domain.c b/xen/arch/arm/domain.c 
index f71b582..2c3b132 100644 
--- a/xen/arch/arm/domain.c 
+++ b/xen/arch/arm/domain.c 
@@ -141,6 +141,8 @@ static void ctxt_switch_to(struct vcpu *n) 
     /* VGIC */ 
     gic_restore_state(n); 
+    local_irq_enable(); 
+ 
     /* XXX VFP */ 
     /* XXX MPU */ 
@@ -215,8 +217,6 @@ static void schedule_tail(struct vcpu *prev) 
 { 
     ctxt_switch_from(prev); 
-    local_irq_enable(); 
- 
     /* TODO 
        update_runstate_area(current); 
     */ 
diff --git a/xen/arch/arm/gic.c b/xen/arch/arm/gic.c 
index d4f0a43..8186ad8 100644 
--- a/xen/arch/arm/gic.c 
+++ b/xen/arch/arm/gic.c 
@@ -81,11 +81,11 @@ void gic_restore_state(struct vcpu *v) 
     if ( is_idle_vcpu(v) ) 
         return; 
-    spin_lock_irq(&gic.lock); 
+    spin_lock(&gic.lock); 
     this_cpu(lr_mask) = v->arch.lr_mask; 
     for ( i=0; i<nr_lrs; i++) 
         GICH[GICH_LR + i] = v->arch.gic_lr[i]; 
-    spin_unlock_irq(&gic.lock); 
+    spin_unlock(&gic.lock); 
     GICH[GICH_APR] = v->arch.gic_apr; 
     GICH[GICH_HCR] = GICH_HCR_EN; 
     isb(); 


best, 
Jaeyong
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