reg_check_chans_work() holds rtnl_mutex for the entire duration of iterating over all registered devices and calling cfg80211_leave() on each invalid wdev. cfg80211_leave() can be slow (disconnect, stop AP, leave mesh), causing rtnl_mutex starvation when many wireless interfaces are present. This results in tasks waiting for rtnl_mutex for longer than hung_task_timeout_secs: INFO: task hung in inet_rtm_newaddr INFO: task hung in inet6_rtm_newaddr INFO: task hung in nsim_destroy INFO: task hung in tun_chr_close INFO: task hung in switchdev_deferred_process_work Fix by walking cfg80211_rdev_list under RCU and acquiring rtnl per-device, so other rtnl waiters get a chance to run between devices. I could not add the Fixes: tag because this patch addresses five separate hung task reports whose cause bisections all failed, making it impossible to identify a single introducing commit. Reported-by: syzbot+adeb8550754921fece20@syzkaller.appspotmail.com Closes: https://syzkaller.appspot.com/bug?extid=adeb8550754921fece20 Reported-by: syzbot+101224300649c3eb8af4@syzkaller.appspotmail.com Closes: https://syzkaller.appspot.com/bug?extid=101224300649c3eb8af4 Reported-by: syzbot+8141dcbd23a8f857798a@syzkaller.appspotmail.com Closes: https://syzkaller.appspot.com/bug?extid=8141dcbd23a8f857798a Reported-by: syzbot+b0ae8f1abf7d891e0426@syzkaller.appspotmail.com Closes: https://syzkaller.appspot.com/bug?extid=b0ae8f1abf7d891e0426 Reported-by: syzbot+d6bbe0f5705cb8a5aa2b@syzkaller.appspotmail.com Closes: https://syzkaller.appspot.com/bug?extid=d6bbe0f5705cb8a5aa2b Signed-off-by: Ömer Mete Kaya --- net/wireless/reg.c | 19 ++++++++++++++----- 1 file changed, 14 insertions(+), 5 deletions(-) diff --git a/net/wireless/reg.c b/net/wireless/reg.c index a8336baf85dc..a2e0d1cf8317 100644 --- a/net/wireless/reg.c +++ b/net/wireless/reg.c @@ -2466,12 +2466,21 @@ static void reg_check_chans_work(struct work_struct *work) struct cfg80211_registered_device *rdev; pr_debug("Verifying active interfaces after reg change\n"); - rtnl_lock(); - - for_each_rdev(rdev) + /* + * Acquire rtnl per-device instead of holding it for the entire loop; + * cfg80211_leave() can be slow and starve other rtnl waiters otherwise. + * wiphy_unregister() holds rtnl across list_del_rcu() + synchronize_rcu(), + * so rdev cannot be freed while we hold rtnl_lock() below. + */ + rcu_read_lock(); + list_for_each_entry_rcu(rdev, &cfg80211_rdev_list, list) { + rcu_read_unlock(); + rtnl_lock(); reg_leave_invalid_chans(&rdev->wiphy); - - rtnl_unlock(); + rtnl_unlock(); + rcu_read_lock(); + } + rcu_read_unlock(); } void reg_check_channels(void) -- 2.55.0