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

[Stefano Stabellini <stefano.stabellini@xxxxxxxxxxxxx>]

On Mon, 3 Feb 2014, Oleksandr Tyshchenko wrote:
> 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>

nice work Oleksandr!

Acked-by: Stefano Stabellini <stefano.stabellini@xxxxxxxxxxxxx>


>  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
> 
> 
> _______________________________________________
> Xen-devel mailing list
> Xen-devel@xxxxxxxxxxxxx
> http://lists.xen.org/xen-devel
> 

_______________________________________________
Xen-devel mailing list
Xen-devel@xxxxxxxxxxxxx
http://lists.xen.org/xen-devel