From: Andrew Gallatin <gallatin@myri.com>
Date: Wed, 31 Oct 2007 21:40:06 +0000 (-0400)
Subject: Fix myri10ge NAPI oops & warnings
X-Git-Tag: v2.6.24-rc2~55^2
X-Git-Url: http://git.openpandora.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=c956a24018819bd903fad0cd275a63c089cdba53;p=pandora-kernel.git

Fix myri10ge NAPI oops & warnings

When testing the myri10ge driver with 2.6.24-rc1, I found
that the machine crashed under heavy load:

Unable to handle kernel paging request at 0000000000100108 RIP:
  [<ffffffff803cc8dd>] net_rx_action+0x11b/0x184

The address corresponds to the list_move_tail() in
netif_rx_complete():
                     if (unlikely(work == weight))
                             list_move_tail(&n->poll_list, list);

Eventually, I traced the crashes to calling netif_rx_complete() with
work_done == budget.  From looking at other drivers, it appears that
one should only call netif_rx_complete() when work_done < budget.

To fix it, I changed the test in myri10ge_poll() so that it refers
to to work_done rather than looking at the rx ring status.  If
work_done is < budget, then that implies we have no more packets to
process. Any races will be resolved by the NIC when the write to
irq_claim is made.

In myri10ge_clean_rx_done(), if we ever exceeded our budget, it would
report a work_done one larger than was acutally done.  This is because
the increment was done in the conditional, so work_done would be
incremented regardless of whether or not the test passed or failed.
This would lead to the WARN_ON_ONCE(work > weight); warning in
net_rx_action triggering.  I've moved the increment of work_done
inside the loop.  Note that this would only be a problem when we had
exceeded our budget.

Signed off by: Andrew Gallatin <gallatin@myri.com>

Andrew Gallatin Myricom Inc

Signed-off-by: Jeff Garzik <jeff@garzik.org>
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