2016-01-25 13:42:43

by Michal Kazior

Subject: [PATCH] mac80211: fix unnecessary frame drops in mesh fwding

The ieee80211_queue_stopped() expects hw queue
number but it was given raw WMM AC number instead.

This could cause frame drops and problems with
traffic in some cases - most notably if driver
doesn't map AC numbers to queue numbers 1:1 and
uses ieee80211_stop_queues() and
ieee80211_wake_queue() only without ever calling
ieee80211_wake_queues().

On ath10k it was possible to hit this problem in
the following case:

1. wlan0 uses queue 0
(ath10k maps queues per vif)
2. offchannel uses queue 15
3. queues 1-14 are unused
4. ieee80211_stop_queues()
5. ieee80211_wake_queue(q=0)
6. ieee80211_wake_queue(q=15)
(other queues are not woken up because both
driver and mac80211 know other queues are
unused)
7. ieee80211_rx_h_mesh_fwding()
8. ieee80211_select_queue_80211() returns 2
9. ieee80211_queue_stopped(q=2) returns true
10. frame is dropped (oops!)

Fixes: d3c1597b8d1b ("mac80211: fix forwarded mesh frame queue mapping")
Signed-off-by: Michal Kazior <[email protected]>
---
net/mac80211/rx.c | 5 +++--
1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/net/mac80211/rx.c b/net/mac80211/rx.c
index ae993edfdecf..664e8861edbe 100644
--- a/net/mac80211/rx.c
+++ b/net/mac80211/rx.c
@@ -2235,7 +2235,7 @@ ieee80211_rx_h_mesh_fwding(struct ieee80211_rx_data *rx)
struct ieee80211_local *local = rx->local;
struct ieee80211_sub_if_data *sdata = rx->sdata;
struct ieee80211_if_mesh *ifmsh = &sdata->u.mesh;
- u16 q, hdrlen;
+ u16 ac, q, hdrlen;

hdr = (struct ieee80211_hdr *) skb->data;
hdrlen = ieee80211_hdrlen(hdr->frame_control);
@@ -2304,7 +2304,8 @@ ieee80211_rx_h_mesh_fwding(struct ieee80211_rx_data *rx)
ether_addr_equal(sdata->vif.addr, hdr->addr3))
return RX_CONTINUE;

- q = ieee80211_select_queue_80211(sdata, skb, hdr);
+ ac = ieee80211_select_queue_80211(sdata, skb, hdr);
+ q = sdata->vif.hw_queue[ac];
if (ieee80211_queue_stopped(&local->hw, q)) {
IEEE80211_IFSTA_MESH_CTR_INC(ifmsh, dropped_frames_congestion);
return RX_DROP_MONITOR;
--
2.1.4

2016-01-26 13:13:40

by Johannes Berg

Subject: Re: [PATCH] mac80211: fix unnecessary frame drops in mesh fwding

On Mon, 2016-01-25 at 14:43 +0100, Michal Kazior wrote:
> The ieee80211_queue_stopped() expects hw queue
> number but it was given raw WMM AC number instead.
>
> This could cause frame drops and problems with
> traffic in some cases - most notably if driver
> doesn't map AC numbers to queue numbers 1:1 and
> uses ieee80211_stop_queues() and
> ieee80211_wake_queue() only without ever calling
> ieee80211_wake_queues().
>
[...]

Yeah, this seems right - applied.

I put it into mac80211-next since you nobody complained before so it's
likely not relevant without your other ath10k patches.

johannes