Re: [PATCH 2/2] mac80211: put upper bound on txqi queue length.

[Michal Kazior]

On 5 December 2016 at 14:56, Johannes Berg  wrote:
> On Tue, 2016-11-29 at 10:05 -0800, gree...@candelatech.com wrote:
>> From: Ben Greear 
>>
>> This fixes OOM when using pktgen to drive a wifi station at more than
>> the station can transmit.  pktgen uses ndo_start_xmit instead of
>> going
>> through the queue layer, so it will not back off when the queues are
>> stopped, and would thus cause packets to be added to the txqi->queue
>> until the system goes OOM and crashes.
>>
>> Signed-off-by: Ben Greear 
>> ---
>>
>> This is against 4.7.10+, not sure if it is actually needed in latest
>> kernel.
>
> One would hope that fq_tin_enqueue() does something like that, but
> anyway the patch doesn't apply so I'm dropping it.

fq_tin_enqueue() drops "fat" flow head packet upon reaching packet
count limit (8192) or memory limit (4 or 16 mbytes depending on vht
availability) whichever is hit first.


Michał

Re: [PATCH 2/2] mac80211: put upper bound on txqi queue length.

[Johannes Berg]

On Tue, 2016-11-29 at 10:05 -0800, gree...@candelatech.com wrote:
> From: Ben Greear 
> 
> This fixes OOM when using pktgen to drive a wifi station at more than
> the station can transmit.  pktgen uses ndo_start_xmit instead of
> going
> through the queue layer, so it will not back off when the queues are
> stopped, and would thus cause packets to be added to the txqi->queue
> until the system goes OOM and crashes.
> 
> Signed-off-by: Ben Greear 
> ---
> 
> This is against 4.7.10+, not sure if it is actually needed in latest
> kernel.

One would hope that fq_tin_enqueue() does something like that, but
anyway the patch doesn't apply so I'm dropping it.

johannes

[PATCH 2/2] mac80211: put upper bound on txqi queue length.

[greearb]

From: Ben Greear 

This fixes OOM when using pktgen to drive a wifi station at more than
the station can transmit.  pktgen uses ndo_start_xmit instead of going
through the queue layer, so it will not back off when the queues are
stopped, and would thus cause packets to be added to the txqi->queue
until the system goes OOM and crashes.

Signed-off-by: Ben Greear 
---

This is against 4.7.10+, not sure if it is actually needed in latest kernel.

 net/mac80211/tx.c | 10 ++
 1 file changed, 10 insertions(+)

diff --git a/net/mac80211/tx.c b/net/mac80211/tx.c
index fbcb5fc..0573ab9 100644
--- a/net/mac80211/tx.c
+++ b/net/mac80211/tx.c
@@ -1293,6 +1293,16 @@ static void ieee80211_drv_tx(struct ieee80211_local 
*local,
goto tx_normal;
 
ac = txq->ac;
+
+   if (atomic_read(>txqs_len[ac]) >=
+   (local->hw.txq_ac_max_pending * 2)) {
+   /* Must be that something is not paying attention to
+* max-pending, like pktgen, so just drop this frame.
+*/
+   ieee80211_free_txskb(>hw, skb);
+   return;
+   }
+
txqi = to_txq_info(txq);
atomic_inc(>txqs_len[ac]);
if (atomic_read(>txqs_len[ac]) >= local->hw.txq_ac_max_pending)
-- 
2.4.11