s390/qeth: implement smarter resizing of the RX buffer pool

The RX buffer pool is allocated in qeth_alloc_qdio_queues().
A subsequent pool resizing is then handled in a very simple way:
first free the current pool, then allocate a new pool of the requested
size.

There's two ways where this can go wrong:
1. if the resize action happens _before_ the initial pool was allocated,
   then a subsequent initialization will call qeth_alloc_qdio_queues()
   and fill the pool with a second(!) set of pages. We consume twice the
   planned amount of memory.
   This is easy to fix - just skip the resizing if the queues haven't
   been allocated yet.
2. if the initial pool was created by qeth_alloc_qdio_queues() but a
   subsequent resizing fails, then the device has no(!) RX buffer pool.
   The next initialization will _not_ call qeth_alloc_qdio_queues(), and
   attempting to back the RX buffers with pages in
   qeth_init_qdio_queues() will fail.
   Not very difficult to fix either - instead of re-allocating the whole
   pool, just allocate/free as many entries to match the desired size.

Fixes: 4a71df50047f ("qeth: new qeth device driver")
Signed-off-by: Julian Wiedmann <jwi@linux.ibm.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 4 insertions, 5 deletions

diff --git a/drivers/s390/net/qeth_l3_sys.c b/drivers/s390/net/qeth_l3_sys.c
index 29f2517d2a31..a3d1c3bdfadb 100644
--- a/drivers/s390/net/qeth_l3_sys.c
+++ b/drivers/s390/net/qeth_l3_sys.c
@@ -206,12 +206,11 @@ static ssize_t qeth_l3_dev_sniffer_store(struct device *dev,
 		qdio_get_ssqd_desc(CARD_DDEV(card), &card->ssqd);
 		if (card->ssqd.qdioac2 & CHSC_AC2_SNIFFER_AVAILABLE) {
 			card->options.sniffer = i;
-			if (card->qdio.init_pool.buf_count !=
-					QETH_IN_BUF_COUNT_MAX)
-				qeth_realloc_buffer_pool(card,
-					QETH_IN_BUF_COUNT_MAX);
-		} else
+			qeth_resize_buffer_pool(card, QETH_IN_BUF_COUNT_MAX);
+		} else {
 			rc = -EPERM;
+		}
+
 		break;
 	default:
 		rc = -EINVAL;