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From: Adrian Chadd <adrian@FreeBSD.org>
Date: Fri, 28 Oct 2011 15:44:09 +0000 (UTC)
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Subject: svn commit: r226884 - head/sys/dev/ath
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Author: adrian
Date: Fri Oct 28 15:44:09 2011
New Revision: 226884
URL: http://svn.freebsd.org/changeset/base/226884

Log:
  When punting frames to the RX tap, free the mbufs since we've tampered with
  their length.
  
  Without this, an error frame mbuf would:
  
  * have its size adjusted;
  * thrown at the radiotap code;
  * then since it's never consumed, the rxbuf/mbuf is then re-added to the
    RX descriptor list with the small size;
  * .. and the hardware ends up (sometimes) only DMA'ing part of a frame into
    the small buffer, chaining RX frames together (setting the more flag).
  
  I discovered this particular issue when doing some promiscuous radiotap
  testing; I found that I'd occasionally get rs_more set in RX descriptors
  w/ the first frame length being very small (sub-100 bytes.) The driver
  handles 2-descriptor RX frames (but not more), so this still worked; it
  was just odd.
  
  This is suboptimal and may benefit from being replaced with caching
  the m_pkthdr_len and m_len fields, then restoring them after completion.

Modified:
  head/sys/dev/ath/if_ath.c

Modified: head/sys/dev/ath/if_ath.c
==============================================================================
--- head/sys/dev/ath/if_ath.c	Fri Oct 28 15:38:11 2011	(r226883)
+++ head/sys/dev/ath/if_ath.c	Fri Oct 28 15:44:09 2011	(r226884)
@@ -3624,8 +3624,10 @@ rx_error:
 				/* NB: bpf needs the mbuf length setup */
 				len = rs->rs_datalen;
 				m->m_pkthdr.len = m->m_len = len;
+				bf->bf_m = NULL;
 				ath_rx_tap(ifp, m, rs, tsf, nf);
 				ieee80211_radiotap_rx_all(ic, m);
+				m_freem(m);
 			}
 			/* XXX pass MIC errors up for s/w reclaculation */
 			goto rx_next;