Date: Mon, 21 May 2012 23:36:49 -0700 From: Adrian Chadd <adrian@freebsd.org> To: freebsd-wireless@freebsd.org Subject: [net80211] Fix some corner cases in BAR TX handling Message-ID: <CAJ-Vmo=uOrK=RB_ezz-A8r=-bNOaV-6%2BqcbGMYGuC3buZZefYw@mail.gmail.com>
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Hi,
This patch fixes a couple of rather annoying corner cases that I've
seen with BAR TX handling in ath(4).
They showed up because I am using a very cut down set of buffers in
ath(4) (128 tx and 128 rx) rather than the older number (512) and I
can easily exhaust them whilst the TID is paused. I'll soon implement
some changes which will leave a "reserved" set of frames for
management - and if I can line all the stars up correctly, have the
management frames go out on the highest priority TX queue.
Specifically:
* ieee80211_send_bar() disables the timer and doesn't restart it
unless ic_raw_xmit() suceeds;
* if the TX fails and the timeout occurs via bar_timeout(), it'll try
calling ieee80211_send_bar() to retransmit - but if that fails, the
timer will never occur.
* Callbacks are only done via bar_tx_complete(), which is not called
if ieee80211_send_bar() fails to queue any frames to the driver.
* If the timer does get started again, BARPEND may have been cleared
(due to a failed ieee80211_send_bar() attempt to call ic_raw_xmit())
and it won't actually be processed, causing the attempts to fail.
Again.
So to maintain some semblence of predicable behaviour, I've done the following:
* The ic_bar_response() handler is called just before AMPDU is
disabled, giving the driver a chance to be told that the max number of
retries has been reached. I don't like how this is the only real way
to know that the BAR TX attempt has totally failed; I'll worry about
that later.
* If a retransmit attempt fails, set BARPEND and restart the timer.
I've verified that this fixes all the weird BAR TX stalls I've seen.
Thanks,
Adrian
Index: net80211/ieee80211_ht.c
===================================================================
--- net80211/ieee80211_ht.c (revision 235772)
+++ net80211/ieee80211_ht.c (working copy)
@@ -2166,6 +2166,9 @@
}
}
+/* XXX */
+static void bar_start_timer(struct ieee80211_tx_ampdu *tap);
+
static void
bar_timeout(void *arg)
{
@@ -2184,11 +2187,34 @@
return;
/* XXX ? */
if (tap->txa_attempts >= ieee80211_bar_maxtries) {
+ struct ieee80211com *ic = ni->ni_ic;
+
ni->ni_vap->iv_stats.is_ampdu_bar_tx_fail++;
+ /*
+ * If (at least) the last BAR TX timeout was due to
+ * an ieee80211_send_bar() failures, then we need
+ * to make sure we notify the driver that a BAR
+ * TX did occur and fail. This gives the driver
+ * a chance to undo any queue pause that may
+ * have occured.
+ */
+ ic->ic_bar_response(ni, tap, 1);
ieee80211_ampdu_stop(ni, tap, IEEE80211_REASON_TIMEOUT);
} else {
ni->ni_vap->iv_stats.is_ampdu_bar_tx_retry++;
- ieee80211_send_bar(ni, tap, tap->txa_seqpending);
+ if (ieee80211_send_bar(ni, tap, tap->txa_seqpending) != 0) {
+ /*
+ * If ieee80211_send_bar() fails here, the
+ * timer may have stopped and/or the pending
+ * flag may be clear. Because of this,
+ * fake the BARPEND and reset the timer.
+ * A retransmission attempt will then occur
+ * during the next timeout.
+ */
+ /* XXX locking */
+ tap->txa_flags |= IEEE80211_AGGR_BARPEND;
+ bar_start_timer(tap);
+ }
}
}
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