On 07.05.22 13:26, Toke Høiland-Jørgensen wrote:
Alexander Wetzel <alexander@xxxxxxxxxxxxxx> writes:
Calling only __ieee80211_select_queue() for control port TX exposes
drivers which do not support QoS to non-zero values in
skb->queue_mapping and even can assign not available queues to
info->hw_queue.
This can cause issues for drivers like we did e.g. see in
'746285cf81dc ("rtl818x: Prevent using not initialized queues")'.
This also prevents a redundant call to __ieee80211_select_queue() when
using control port TX with iTXQ (pull path).
And it starts to prioritize 802.11 preauthentication frames
(ETH_P_PREAUTH) on all TX paths.
Pierre Asselin confirmed that this patch indeed prevents crashing his
system without '746285cf81dc ("rtl818x: Prevent using not initialized
queues")'.
Tested-by: Pierre Asselin <pa@xxxxxxxxx>
Signed-off-by: Alexander Wetzel <alexander@xxxxxxxxxxxxxx>
---
Starting to prioritize ETH_P_PREAUTH was just added since I noticed that
contradictory to at least my expectations control port does accept
ETH_P_PREAUTH but handles these like a normal frame for the priority.
That can be broken out or even drop, when needed.
While looking at the code I also tripped over multiple other questions
and I'll probably propose a much more invasive change how to handle
the queue assignment. (End2end we seem to do some quite stupid things.)
Additionally I really don't get why we call skb_get_hash() on queue
assignment:
I found the commit '180ac48ee62f ("mac80211: calculate skb hash early
when using itxq")' but don't see why calculating the hash early is
useful. Any hints here are appreciated. fq_flow_idx() seems to do that
when needed and I can't find any other usage of the hash...
The commit message of that commit has a hint:
This avoids flow separation issues when using software encryption.
The idea being that the packet contents can change on encryption, but
skb->hash is preserved, so you want it to run before encryption happens
to keep flows in the same queue.
However, AFAICT ieee80211_tx_h_encrypt() is called after frames are
dequeued from the TXQs, so not actually sure this is needed. Adding
Felix, in the hope that he can explain the reasoning behind that commit :)Sorry, I don't remember the details on that one. One advantage that I
can think of (which isn't mentioned in the commit msg) is that it is
likely better for performance to calculate the hash early since there is
a good chance that more of the skb data is still in the CPU cache.
- Felix
