Hi,

Upstream commit 1474bc87fe57 ("wifi: cfg80211: check wiphy mutex is held for wdev mutex") has been backported recently to 5.15/6.1/6.6 stable branches. After that we started seeing numerous lockdep assertion splats in these kernels originating from different parts of wireless stack where wdev_lock() is called. There is also a huge pile of them already found in Syzbot [1,2,3].

Digging more into the issue it appears that the blamed commit is a part of a much larger series [4] with locking cleanups and improvements for the whole wireless subsystem. The series was merged at 6.7.

The cover letter for the series says: There's a kind of pointless commit in there that adds some wiphy locking assertions to the wdev as an intermediate step, I can remove that if you think that's better. We ran with it at that intermediate stage for a while to test things.

So backporting this commit to stable branches without taking the series as a whole is pointless and just leads to bogus lockdep assertion splats there. The series itself is an improvement and cleanup work and therefore is not considered as material for old stable kernels.

The solution which comes to mind is to revert this backported patch from the affected stable branches.

Namely: - 5.15 https://lore.kernel.org/stable/20240901160825.013135421@linuxfoundation.org/ - 6.1 https://lore.kernel.org/stable/20240827143842.546537850@linuxfoundation.org/ - 6.6 https://lore.kernel.org/stable/20240827143846.794100356@linuxfoundation.org/

The intention why it was suddenly backported to these branches a year after merge-to-upstream is not clear actually: there are no stable or Fixes tags in commit message, and I don't find any public request for explicit backport on mailing lists.

Please let me know if you can revert the commits yourself or I have to prepare and send them to you.

[1]: https://syzkaller.appspot.com/bug?extid=310a1a9715fc1c9ead61 [2]: https://syzkaller.appspot.com/bug?extid=b730e8b6bc76d07fe10b [3]: https://syzkaller.appspot.com/bug?extid=09501cf606ec2823fafa [4]: https://lore.kernel.org/linux-wireless/20230828115927.116700-41-johannes@sip...

-- Thanks, Fedor