On Thu, 23 Apr 2020 at 02:29, Hauke Mehrtens hauke@hauke-m.de wrote:

Hi,

Since commit 52e04b4ce5d0 ("mac80211: fix race in ieee80211_register_hw()") the debugfs entries for mac80211 drivers are broken. https://git.kernel.org/linus/52e04b4ce5d03775b6a78f3ed1097480faacc9fd

Felix reported that the file /sys/kernel/debug/ieee80211/phy0/rc is now located at /sys/kernel/debug/rc.

Before this commit we had the following flow:

1. wiphy_register()

-> creates /sys/kernel/debug/ieee80211/phy0/ -> fill rdev->wiphy.debugfsdir pointer 2. ieee80211_init_rate_ctrl_alg() -> call rate_control_alloc() -> use rdev->wiphy.debugfsdir pointer to create /sys/kernel/debug/ieee80211/phy0/rc/

This works like expected.

With the commit the flow in ieee80211_register_hw() is the other way around: 2. ieee80211_init_rate_ctrl_alg() -> call rate_control_alloc() -> use rdev->wiphy.debugfsdir pointer (now NULL) to create /sys/kernel/debug/rc/ 2. wiphy_register() -> creates /sys/kernel/debug/ieee80211/phy0/ -> fill rdev->wiphy.debugfsdir pointer

Thanks for the detailed report. I missed to notice this hidden debugfs dependency on "wiphy_register()". To address this issue, I think it's reasonable to move creation of wiphy debugfs directory during allocation of wiphy device as per following change (untested though):

diff --git a/net/wireless/core.c b/net/wireless/core.c index 341402b..239e9ff 100644 --- a/net/wireless/core.c +++ b/net/wireless/core.c @@ -473,6 +473,10 @@ struct wiphy *wiphy_new_nm(const struct cfg80211_ops *ops, int sizeof_priv, } }

+ /* add to debugfs */ + rdev->wiphy.debugfsdir = debugfs_create_dir(wiphy_name(&rdev->wiphy), + ieee80211_debugfs_dir); + INIT_LIST_HEAD(&rdev->wiphy.wdev_list); INIT_LIST_HEAD(&rdev->beacon_registrations); spin_lock_init(&rdev->beacon_registrations_lock); @@ -903,10 +907,6 @@ int wiphy_register(struct wiphy *wiphy) list_add_rcu(&rdev->list, &cfg80211_rdev_list); cfg80211_rdev_list_generation++;

- /* add to debugfs */ - rdev->wiphy.debugfsdir = debugfs_create_dir(wiphy_name(&rdev->wiphy), - ieee80211_debugfs_dir); - cfg80211_debugfs_rdev_add(rdev); nl80211_notify_wiphy(rdev, NL80211_CMD_NEW_WIPHY);

With this change we can remove this hidden debugfs dependency. Please give it a try and let me know if it works for you.

-Sumit

This patch was backported to multiple stable kernel versions: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?h=l...

Hauke