On 08.03.23 12:41, Alexander Wetzel wrote:
On 08.03.23 08:52, Felix Fietkau wrote:
I'm also planning to provide some more debug patches, to figuring out
which part of commit 4444bc2116ae ("wifi: mac80211: Proper mark iTXQs
for resumption") fixes the issue for you. Assuming my understanding
above is correct the patch should not really fix/break anything for
you...With the findings above I would have expected your git bisec to
identify commit a790cc3a4fad ("wifi: mac80211: add wake_tx_queue
callback to drivers") as the first broken commit...
I can't point to any specific series of events where it would go wrong,
but I suspect that the problem might be the fact that you're doing tx
scheduling from within ieee80211_handle_wake_tx_queue. I don't see how
it's properly protected from potentially being called on different CPUs
concurrently.
Back when I was debugging some iTXQ issues in mt76, I also had problems
when tx scheduling could happen from multiple places. My solution was to
have a single worker thread that handles tx, which is scheduled from the
wake_tx_queue op.
Maybe you could do something similar in mac80211 for non-iTXQ drivers.
I think it's already doing all of that:
ieee80211_handle_wake_tx_queue() is the mac80211 implementation for the
wake_tx_queue op. The drivers without native iTXQ support simply link it
to this handler.
I know. The problem I see is that I can't find anything that guarantees
that .wake_tx_queue_op is not being called concurrently from multiple
different places. ieee80211_handle_wake_tx_queue is doing the scheduling
directly, instead of deferring it to a single workqueue/tasklet/thread,
and multiple concurrent calls to it could potentially cause issues.
- Felix
