Commit 5091730d authored by Ido Schimmel's avatar Ido Schimmel Committed by David S. Miller

mlxsw: pci: Correctly determine if descriptor queue is full

The descriptor queues for sending (SDQs) and receiving (RDQs) packets
are managed by two counters - producer and consumer - which are both
16-bit in size. A queue is considered full when the difference between
the two equals the queue's maximum number of descriptors.

However, if the producer counter overflows, then it's possible for the
full queue check to fail, as it doesn't take the overflow into account.
In such a case, descriptors already passed to the device - but for which
a completion has yet to be posted - will be overwritten, thereby causing
undefined behavior. The above can be achieved under heavy load (~30
netperf instances).

Fix that by casting the subtraction result to u16, preventing it from
being treated as a signed integer.

Fixes: eda6500a ("mlxsw: Add PCI bus implementation")
Signed-off-by: default avatarIdo Schimmel <idosch@mellanox.com>
Signed-off-by: default avatarJiri Pirko <jiri@mellanox.com>
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
parent 912b1c89
......@@ -215,7 +215,7 @@ mlxsw_pci_queue_elem_info_producer_get(struct mlxsw_pci_queue *q)
{
int index = q->producer_counter & (q->count - 1);
if ((q->producer_counter - q->consumer_counter) == q->count)
if ((u16) (q->producer_counter - q->consumer_counter) == q->count)
return NULL;
return mlxsw_pci_queue_elem_info_get(q, index);
}
......
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