[Bug 225408] re_rxeof erroneously returns EAGAIN, resulting in unnecessary processing

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https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=225408

Mark Johnston <markj at FreeBSD.org> changed:

           What    |Removed                     |Added
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                 CC|                            |markj at FreeBSD.org

--- Comment #1 from Mark Johnston <markj at FreeBSD.org> ---
I also noticed this while adding netdump hooks to re(4). The code seems broken
even with your patch applied.

In the legacy interrupt task handler we have:

2580         status = CSR_READ_2(sc, RL_ISR);                                   
2581         CSR_WRITE_2(sc, RL_ISR, status);
...
2596         if (status & (RL_ISR_RX_OK|RL_ISR_RX_ERR|RL_ISR_FIFO_OFLOW))       
2597                 rval = re_rxeof(sc, NULL);
...
2629         if ((CSR_READ_2(sc, RL_ISR) & RL_INTRS_CPLUS) || rval) {           
2630                 taskqueue_enqueue(taskqueue_fast, &sc->rl_inttask);        
2631                 return;                                                    
2632         }                                                                  
2633                                                                            
2634         CSR_WRITE_2(sc, RL_IMR, RL_INTRS_CPLUS);

with rval initialized to 0.

So, we initially clear the bits in the ISR by writing status back, and pull
packets off the rx ring if we had received a packet. If another interrupt came
in while processing, or rx_rxeof() returned EAGAIN, we'll reschedule the task
handler, else we're done and we unmask interrupts. In the case where rx_rxeof()
hit the processing limit, though, we'll only call rx_rxeof() again if another
rx interrupt was raised. So it seems that this EAGAIN check really isn't
accomplishing much.

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