KVM: arm/arm64: vgic: Fix potential deadlock when ap_list is long

[ Upstream commit d4a8061a7c5f7c27a2dc002ee4cb89b3e6637e44 ]

If the ap_list is longer than 256 entries, merge_final() in list_sort()
will call the comparison callback with the same element twice, causing
a deadlock in vgic_irq_cmp().

Fix it by returning early when irqa == irqb.

Cc: stable@vger.kernel.org # 4.7+
Fixes: 8e4447457965 ("KVM: arm/arm64: vgic-new: Add IRQ sorting")
Signed-off-by: Zenghui Yu <yuzenghui@huawei.com>
Signed-off-by: Heyi Guo <guoheyi@huawei.com>
[maz: massaged commit log and patch, added Fixes and Cc-stable]
Signed-off-by: Marc Zyngier <maz@kernel.org>
Signed-off-by: Will Deacon <will@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>

diff --git a/virt/kvm/arm/vgic/vgic.c b/virt/kvm/arm/vgic/vgic.c
index 9d4e01f109499c41374375e0a553a8da343c8628..07ee8e4e00a215a381164a02c44ffd672ed27c6d 100644 (file)
--- a/virt/kvm/arm/vgic/vgic.c
+++ b/virt/kvm/arm/vgic/vgic.c
@@ -199,6 +199,13 @@ static int vgic_irq_cmp(void *priv, struct list_head *a, struct list_head *b)
        bool penda, pendb;
        int ret;
 
+       /*
+        * list_sort may call this function with the same element when
+        * the list is fairly long.
+        */
+       if (unlikely(irqa == irqb))
+               return 0;
+
        spin_lock(&irqa->irq_lock);
        spin_lock_nested(&irqb->irq_lock, SINGLE_DEPTH_NESTING);