[Xen-devel] [PATCH v1] xen/arm: Fix deadlock in gic_set_guest_irq()

[Oleksandr Tyshchenko <oleksandr.tyshchenko@xxxxxxxxxxxxxxx>]

The possible deadlock scenario is explained below:

non interrupt context:    interrupt contex        interrupt context
                          (CPU0):                 (CPU1):
vgic_distr_mmio_write()   do_trap_irq()           do_softirq()
  |                         |                       |
  vgic_disable_irqs()       ...                     ...
    |                         |                       |
    gic_remove_from_queues()  vgic_vcpu_inject_irq()  vgic_vcpu_inject_irq()
    |  ...                      |                       |
    |  spin_lock(...)           gic_set_guest_irq()     gic_set_guest_irq()
    |  ...                        ...                     ...
    |  ... <----------------.---- spin_lock_irqsave(...)  ...
    |  ... <----------------.-.---------------------------spin_lock_irqsave(...)
    |  ...                  . .       Oops! The lock has already taken.
    |  spin_unlock(...)     . .
    |  ...                  . .
    gic_irq_disable()       . .
       ...                  . .
       spin_lock(...)       . .
       ...                  . .
       ... <----------------. .
       ... <------------------.
       ...
       spin_unlock(...)

Since the gic_remove_from_queues() and gic_irq_disable() called from
non interrupt context and they acquire the same lock as gic_set_guest_irq()
which called from interrupt context we must disable interrupts in these
functions to avoid possible deadlocks.

Change-Id: Ia354d87bb44418956e30cd7e49cc76616c359cc9
Signed-off-by: Oleksandr Tyshchenko <oleksandr.tyshchenko@xxxxxxxxxxxxxxx>
---
 xen/arch/arm/gic.c |   10 ++++++----
 1 file changed, 6 insertions(+), 4 deletions(-)

diff --git a/xen/arch/arm/gic.c b/xen/arch/arm/gic.c
index c44a4d0..7d83b0c 100644
--- a/xen/arch/arm/gic.c
+++ b/xen/arch/arm/gic.c
@@ -147,14 +147,15 @@ static void gic_irq_enable(struct irq_desc *desc)
 static void gic_irq_disable(struct irq_desc *desc)
 {
     int irq = desc->irq;
+    unsigned long flags;
 
-    spin_lock(&desc->lock);
+    spin_lock_irqsave(&desc->lock, flags);
     spin_lock(&gic.lock);
     /* Disable routing */
     GICD[GICD_ICENABLER + irq / 32] = (1u << (irq % 32));
     desc->status |= IRQ_DISABLED;
     spin_unlock(&gic.lock);
-    spin_unlock(&desc->lock);
+    spin_unlock_irqrestore(&desc->lock, flags);
 }
 
 static unsigned int gic_irq_startup(struct irq_desc *desc)
@@ -658,11 +659,12 @@ static inline void gic_add_to_lr_pending(struct vcpu *v, 
unsigned int irq,
 void gic_remove_from_queues(struct vcpu *v, unsigned int virtual_irq)
 {
     struct pending_irq *p = irq_to_pending(v, virtual_irq);
+    unsigned long flags;
 
-    spin_lock(&gic.lock);
+    spin_lock_irqsave(&gic.lock, flags);
     if ( !list_empty(&p->lr_queue) )
         list_del_init(&p->lr_queue);
-    spin_unlock(&gic.lock);
+    spin_unlock_irqrestore(&gic.lock, flags);
 }
 
 void gic_set_guest_irq(struct vcpu *v, unsigned int virtual_irq,
-- 
1.7.9.5


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