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Commit 12472af8 authored by Julian Wiedmann's avatar Julian Wiedmann Committed by David S. Miller
Browse files

s390/qeth: fix overestimated count of buffer elements 



qeth_get_elements_for_range() doesn't know how to handle a 0-length
range (ie. start == end), and returns 1 when it should return 0.
Such ranges occur on TSO skbs, where the L2/L3/L4 headers (and thus all
of the skb's linear data) are skipped when mapping the skb into regular
buffer elements.

This overestimation may cause several performance-related issues:
1. sub-optimal IO buffer selection, where the next buffer gets selected
   even though the skb would actually still fit into the current buffer.
2. forced linearization, if the element count for a non-linear skb
   exceeds QETH_MAX_BUFFER_ELEMENTS.

Rather than modifying qeth_get_elements_for_range() and adding overhead
to every caller, fix up those callers that are in risk of passing a
0-length range.

Fixes: 2863c613 ("qeth: refactor calculation of SBALE count")
Signed-off-by: default avatarJulian Wiedmann <jwi@linux.vnet.ibm.com>
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
parent 590399dd

drivers/s390/net/qeth_core_main.c

+6 −4
Original line number Diff line number Diff line
@@ -3898,10 +3898,12 @@ EXPORT_SYMBOL_GPL(qeth_get_elements_for_frags); 
int qeth_get_elements_no(struct qeth_card *card,

		     struct sk_buff *skb, int extra_elems, int data_offset)

{

	int elements = qeth_get_elements_for_range(

				(addr_t)skb->data + data_offset,

				(addr_t)skb->data + skb_headlen(skb)) +

			qeth_get_elements_for_frags(skb);

	addr_t end = (addr_t)skb->data + skb_headlen(skb);

	int elements = qeth_get_elements_for_frags(skb);

	addr_t start = (addr_t)skb->data + data_offset;



	if (start != end)

		elements += qeth_get_elements_for_range(start, end);



	if ((elements + extra_elems) > QETH_MAX_BUFFER_ELEMENTS(card)) {

		QETH_DBF_MESSAGE(2, "Invalid size of IP packet "

drivers/s390/net/qeth_l3_main.c

+6 −5
Original line number Diff line number Diff line
@@ -2450,11 +2450,12 @@ static void qeth_tso_fill_header(struct qeth_card *card, 
static int qeth_l3_get_elements_no_tso(struct qeth_card *card,

			struct sk_buff *skb, int extra_elems)

{

	addr_t tcpdptr = (addr_t)tcp_hdr(skb) + tcp_hdrlen(skb);

	int elements = qeth_get_elements_for_range(

				tcpdptr,

				(addr_t)skb->data + skb_headlen(skb)) +

				qeth_get_elements_for_frags(skb);

	addr_t start = (addr_t)tcp_hdr(skb) + tcp_hdrlen(skb);

	addr_t end = (addr_t)skb->data + skb_headlen(skb);

	int elements = qeth_get_elements_for_frags(skb);



	if (start != end)

		elements += qeth_get_elements_for_range(start, end);



	if ((elements + extra_elems) > QETH_MAX_BUFFER_ELEMENTS(card)) {

		QETH_DBF_MESSAGE(2,