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

[Julien Grall <julien.grall@xxxxxxxxxx>]

Forget to add George.

On 02/03/2014 05:51 PM, Julien Grall wrote:
> (+ Xen ARM maintainers)
> 
> Hello Oleksandr,
> 
> Thanks for the patch. For next time, can you add the Xen ARM maintainers
> in cc? With the amount of mail in the mailing list, your mail could be
> lost easily. :)
> 
> On 02/03/2014 05:33 PM, 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>
> Acked-by: Julien Grall <julien.grall@xxxxxxxxxx>
> 
> I think this patch should have a release exception for Xen 4.4. It's fix
> a race condition in the interrupt management.
> 
>> ---
>>  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,
>>
> 
> 


-- 
Julien Grall

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