[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.

[Stefano Stabellini <sstabellini@xxxxxxxxxx>]

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.

Signed-off-by: Stefano Stabellini <sstabellini@xxxxxxxxxx>
---
 xen/arch/arm/gic.c         | 2 +-
 xen/arch/arm/vgic.c        | 4 +---
 xen/include/asm-arm/vgic.h | 1 +
 3 files changed, 3 insertions(+), 4 deletions(-)

diff --git a/xen/arch/arm/gic.c b/xen/arch/arm/gic.c
index 51148b4..28ab2f9 100644
--- a/xen/arch/arm/gic.c
+++ b/xen/arch/arm/gic.c
@@ -509,7 +509,7 @@ static void gic_update_one_lr(struct vcpu *v, int i)
             list_del_init(&p->inflight);
             if ( test_and_clear_bit(GIC_IRQ_GUEST_MIGRATING, &p->status) )
             {
-                struct vcpu *v_target = vgic_get_target_vcpu(v, irq);
+                struct vcpu *v_target = __vgic_get_target_vcpu(v, irq);
                 irq_set_affinity(p->desc, cpumask_of(v_target->processor));
             }
             /* 
diff --git a/xen/arch/arm/vgic.c b/xen/arch/arm/vgic.c
index cceac24..c89b85f 100644
--- a/xen/arch/arm/vgic.c
+++ b/xen/arch/arm/vgic.c
@@ -221,12 +221,10 @@ int vcpu_vgic_free(struct vcpu *v)
 }
 
 /* The function should be called by rank lock taken. */
-static struct vcpu *__vgic_get_target_vcpu(struct vcpu *v, unsigned int virq)
+struct vcpu *__vgic_get_target_vcpu(struct vcpu *v, unsigned int virq)
 {
     struct vgic_irq_rank *rank = vgic_rank_irq(v, virq);
 
-    ASSERT(spin_is_locked(&rank->lock));
-
     return v->domain->vcpu[rank->vcpu[virq & INTERRUPT_RANK_MASK]];
 }
 
diff --git a/xen/include/asm-arm/vgic.h b/xen/include/asm-arm/vgic.h
index dce2f84..26594b0 100644
--- a/xen/include/asm-arm/vgic.h
+++ b/xen/include/asm-arm/vgic.h
@@ -295,6 +295,7 @@ extern int domain_vgic_init(struct domain *d, unsigned int 
nr_spis);
 extern void domain_vgic_free(struct domain *d);
 extern int vcpu_vgic_init(struct vcpu *v);
 extern struct vcpu *vgic_get_target_vcpu(struct vcpu *v, unsigned int virq);
+extern struct vcpu *__vgic_get_target_vcpu(struct vcpu *v, unsigned int virq);
 extern void vgic_vcpu_inject_irq(struct vcpu *v, unsigned int virq);
 extern void vgic_vcpu_inject_spi(struct domain *d, unsigned int virq);
 extern void vgic_clear_pending_irqs(struct vcpu *v);
-- 
1.9.1


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