Re: [Xen-devel] [PATCH v2 4/4] The locking order is: first rank lock, then vgic lock. The order is respected everywhere, except for gic_update_one_lr.

[Julien Grall <julien.grall@xxxxxxx>]

Hi Stefano,

On 22/12/16 02:15, Stefano Stabellini wrote:
> gic_update_one_lr is called with the vgic lock held, but it calls
> vgic_get_target_vcpu, which tries to obtain the rank lock. This can
> cause deadlocks.
>
> We already have a version of vgic_get_target_vcpu that doesn't take the
> rank lock: __vgic_get_target_vcpu.
>
> Solve the lock inversion problem, by not taking the rank lock in
> gic_update_one_lr (calling __vgic_get_target_vcpu instead of
> vgic_get_target_vcpu).  This is safe, because vcpu target modifications
> are protected by the same vgic vcpu lock.
I maintain what I said on the first version of this patch. All this 
patch could be simplified by moving the call to irq_set_affinity in 
vgic_irq_migrate.
There are no restriction to do that and no need to have any lock taken 
but the rank lock.
Regards,

--
Julien Grall

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