netdev - [PATCH]: Fix myri10ge NAPI oops & warnings

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Date:	Wed, 31 Oct 2007 17:40:06 -0400
From:	Andrew Gallatin <gallatin@...i.com>
To:	shemminger@...ux-foundation.org
CC:	jeff@...zik.org, netdev@...r.kernel.org
Subject: [PATCH]: 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@...i.com>

Andrew Gallatin Myricom Inc

View attachment "myri10ge-napi-oops.diff" of type "text/plain" (1361 bytes)