On 08.03.23 13:21, Linux regression tracking (Thorsten Leemhuis) wrote:
On 08.03.23 12:57, Felix Fietkau wrote:
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.
Alexander, Felix, many thx for looking into this.
This more and more sounds like something that might take a while to get
fixed, which makes it harder to get this fixed within those time-frames
Documentation/process/handling-regressions.rst outlines. So please allow
me to ask:
Is reverting the culprit (and reapplying it later once the real cause is
found and fixed) an option, or would that cause other regressions?
This patch turned out to fix a (much worse) pre-release regression. See e.g.
https://lore.kernel.org/linux-wireless/7cff27f8-d363-bbfb-241e-8d6fc0009c40@xxxxxxxxxxxxx/T/#t
To fix both regressions will force us to revert more commits other
patches depends on...
Ciao, Thorsten (wearing his 'the Linux kernel's regression tracker' hat)
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