kern/165866: commit references a PR

[dfilter service]

The following reply was made to PR kern/165866; it has been noted by GNATS.

From: dfilter at FreeBSD.ORG (dfilter service)
To: bug-followup at FreeBSD.org
Cc:  
Subject: Re: kern/165866: commit references a PR
Date: Thu,  8 Mar 2012 23:53:47 +0000 (UTC)

 Author: adrian
 Date: Thu Mar  8 23:53:38 2012
 New Revision: 232707
 URL: http://svn.freebsd.org/changeset/base/232707
 
 Log:
   Correctly initialise the TXQ link pointer to the last descriptor in
   the last buffer in the list.
   
   The current behaviour (due to me, so pointy hat is firmly on my head here)
   was incorrect - it was setting the link pointer to the last descriptor
   of the _first_ buffer in the TXQ.  Instead, it should have set it to the
   last descriptor in the _last_ buffer in the TXQ.
   
   This showed up as occasional TX stalls with frames in the TXQ but no
   TX progress being made.  Further inspection showed the TXQ looked like
   it contained multiple "lists" of frames - there'd be a list of correct
   frames, then a NULL link pointer, but there'd be a next buffer in the
   list.
   
   Since this code is only called upon an interface reset, it's likely
   this only began showing up when I started doing stress testing
   in environments which annoy the radios enough to cause lockups.
   
   I've not yet any TX stalls with this patch applied.
   
   PR:		kern/165866
 
 Modified:
   head/sys/dev/ath/if_ath_tx.c
 
 Modified: head/sys/dev/ath/if_ath_tx.c
 ==============================================================================
 --- head/sys/dev/ath/if_ath_tx.c	Thu Mar  8 23:52:22 2012	(r232706)
 +++ head/sys/dev/ath/if_ath_tx.c	Thu Mar  8 23:53:38 2012	(r232707)
 @@ -623,19 +623,22 @@ void
  ath_txq_restart_dma(struct ath_softc *sc, struct ath_txq *txq)
  {
  	struct ath_hal *ah = sc->sc_ah;
 -	struct ath_buf *bf;
 +	struct ath_buf *bf, *bf_last;
  
  	ATH_TXQ_LOCK_ASSERT(txq);
  
  	/* This is always going to be cleared, empty or not */
  	txq->axq_flags &= ~ATH_TXQ_PUTPENDING;
  
 +	/* XXX make this ATH_TXQ_FIRST */
  	bf = TAILQ_FIRST(&txq->axq_q);
 +	bf_last = ATH_TXQ_LAST(txq, axq_q_s);
 +
  	if (bf == NULL)
  		return;
  
  	ath_hal_puttxbuf(ah, txq->axq_qnum, bf->bf_daddr);
 -	txq->axq_link = &bf->bf_lastds->ds_link;
 +	txq->axq_link = &bf_last->bf_lastds->ds_link;
  	ath_hal_txstart(ah, txq->axq_qnum);
  }
  
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