Re: 5.14-rc3 lockdep warning, iwlwifi 9560

[Johannes Berg <johannes@sipsolutions.net>]

Hi Chris,

Sorry for the late reply.

> [   17.384143] ======================================================
> [   17.384144] WARNING: possible circular locking dependency detected
> [   17.384146] 5.14.0-0.rc3.29.fc35.x86_64+debug #1 Not tainted
> [   17.384147] ------------------------------------------------------
> [   17.384148] kworker/u16:8/554 is trying to acquire lock:
> [   17.384149] ffff91e2af7d80e8 (&sta->rate_ctrl_lock){+.-.}-{2:2},
> at: rate_control_get_rate+0xc0/0x140 [mac80211]
> [   17.384197]
>                but task is already holding lock:
> [   17.384198] ffff91e2af7d8130 (&sta->lock){+.-.}-{2:2}, at:
> ieee80211_stop_tx_ba_cb+0x2e/0x1e0 [mac80211]
> [   17.384229]
> 
> dmesg:
> https://drive.google.com/file/d/1A5aZNMf_qXFU6arthGyu_FEIYV08V7wv/view?usp=sharing

I can confirm this is a problem, basically we have

aggregation start:
 * take sta's rate lock
 * call driver's rate control
 * that decides to start aggregation
 * calls ieee80211_start_tx_ba_session()
 * takes sta lock

aggregation stop:
 * ieee80211_stop_tx_ba_cb() is called
 * takes sta lock
 * releases TXQ from aggregation-related stop by
   calling ieee80211_agg_start_txq()
 * calls schedule_and_wake_txq()
 * calls driver
 * driver retrieves from, which calls rate control
 * takes sta's rate lock


If you could, I'd appreciate if you filed a bug report on bugzilla.kernel.org (see also
https://wireless.wiki.kernel.org/en/users/drivers/iwlwifi/debugging#how_to_report
for the product/component)

It's not obvious to me immediately how to fix it, so I'd prefer to track
it as a bug report.

johannes