xen/arm: Fix deadlock in gic_set_guest_irq()

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@globallogic.com>
Acked-by: Stefano Stabellini <stefano.stabellini@eu.citrix.com>
Acked-by: Julien Grall <julien.grall@linaro.org>
Acked-by: Ian Campbell <ian.campbell@citrix.com>

diff --git a/xen/arch/arm/gic.c b/xen/arch/arm/gic.c
index e6257a7ada3434348bdc8b9020c3fd8c09887a2f..13bbf48c5b6d1bcac8df1fe321d49321d0fad09d 100644 (file)
--- 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)
@@ -652,11 +653,12 @@ 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,