Kernel oops while routing

Ricardo Scop scop at
Wed Dec 5 14:24:57 EST 2001


I apologize for the delay. We were conducting some more tests so as to
not make any more false alarms :-) about kernel crashes, memory leaks
and/or performance problems in the linuxppc port to our 8255 hardware

So, after a _carefull_ test period, these are our findings:

1 - Andy's patch (which is attached) works well and does _not_
append any performance penalties in our tests (we were having PHY
negatiation problems there, again :-/ ).

2 - We _did_ have a memory leak which was causing a kernel crash after
a while, and it _was_ solved by Andy's patch (thanks, Andy!). I believe
it's still on linuxppc_2_4, _2_4_devel and _2_5. It goes like this:

     - in fcc_enet_start_xmit, after setting up another bd and
     incrementing bdp, the next bd's tx-ready bit is tested in order
     to stop the xmit queue if it is set, ok? But, sometimes, the CPM
     may already have cleared this bit _and_ the corresponding
     interrupt has not been serviced yet (because we're in a
     spin_lock_irq); so, netif_stop_queue is not called in this case,
     nor is tx_full set;

     - next, the interrupt is serviced, but then curr_tx equals
     dirty_tx _and_ tx_full is not set, so no sk_buffers are freed!

     - next time fcc_enet_start_xmit is called, tx_ready bit is still
     cleared and the next bd is used, but the corresponding sk_buffer
     wasn't freed, and it's pointer is now lost;

     - cep->lock can't help with this problem, because the CPM is not
     bothered by that 8-). AFAIK, Andy's solution is a good one.

So, we're offering this patch to the public list (with Andy's
blessing :-). I can provide any other details about our tests, if


Ricardo Scop                            mailto:scop at
R SCOP Consulting

"What's money? A man is a success if he gets up in the morning and
goes to bed at night and in between does what he wants to do."
~Bob Dylan

Thursday, November 29, 2001, 7:42:24 PM, you wrote:

DM> Ricardo Scop wrote:

>> I'm kind of lost with this performance variations. As far as I could
>> see, the patch did not insert much processing overhead, so...

DM> Perhaps if someone would post the patch for the rest of us to see we
DM> could be of some assistance.

DM>         -- Dan
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