s390/qeth: fix overestimated count of buffer elements

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[ Upstream commit 12472af896 ]

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: 2863c61334 ("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>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

...

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Julian Wiedmann 2018-02-27 18:58:12 +01:00 • committed by Greg Kroah-Hartman

parent 128c7e6923

commit fa4919e37f

2 changed files with 12 additions and 9 deletions

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10

drivers/s390/net/qeth_core_main.c

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11

drivers/s390/net/qeth_l3_main.c

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