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s390/qeth: fix overestimated count of buffer elements

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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: 2863c61334aa ("qeth: refactor calculation of SBALE count")
Signed-off-by: Julian Wiedmann <jwi@linux.vnet.ibm.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
Julian Wiedmann 2018-02-27 18:58:12 +01:00 committed by David S. Miller
parent 590399ddf9
commit 12472af896
2 changed files with 12 additions and 9 deletions
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10
drivers/s390/net/qeth_core_main.c
View File

@ -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 "

11
drivers/s390/net/qeth_l3_main.c
View File

@ -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,