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ath5k: fix race condition in tx desc processing

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As pointed out by Benoit Papillault, there is a potential
race condition between the host and the hardware in reading
the next link in the transmit descriptor list:

cpu0              hw
                  tx for buf completed
                  raise tx_ok interrupt
process buf
buf->ds_link = 0
                  read buf->ds_link

This change checks txdp before processing a descriptor
(if there are any subsequent descriptors) to see if
hardware moved on.  We'll then process this descriptor on
the next tasklet.

Signed-off-by: Bob Copeland <me@bobcopeland.com>
Acked-by: Bruno Randolf <br1@einfach.org>
Signed-off-by: John W. Linville <linville@tuxdriver.com>
This commit is contained in:
Bob Copeland 2010-04-07 23:55:58 -04:00 committed by John W. Linville
parent 6b5d117edd
commit a05988bbbe
1 changed files with 11 additions and 0 deletions
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11
drivers/net/wireless/ath/ath5k/base.c
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@ -2083,6 +2083,17 @@ ath5k_tx_processq(struct ath5k_softc *sc, struct ath5k_txq *txq)
list_for_each_entry_safe(bf, bf0, &txq->q, list) {
ds = bf->desc;
/*
* It's possible that the hardware can say the buffer is
* completed when it hasn't yet loaded the ds_link from
* host memory and moved on. If there are more TX
* descriptors in the queue, wait for TXDP to change
* before processing this one.
*/
if (ath5k_hw_get_txdp(sc->ah, txq->qnum) == bf->daddr &&
!list_is_last(&bf->list, &txq->q))
break;
ret = sc->ah->ah_proc_tx_desc(sc->ah, ds, &ts);
if (unlikely(ret == -EINPROGRESS))
break;