On 3/25/2022 9:04 AM, Johannes Berg wrote:
On Fri, 2022-03-25 at 08:59 -0700, Jeff Johnson wrote:
On 3/25/2022 5:09 AM, Johannes Berg wrote:
On Tue, 2022-03-22 at 21:58 +0000, William McVicker wrote:
It would be nice if nl80211_vendor_cmd() could support taking the RTNL lock if
requested via the vendor flags. That would require moving the wiphy lock to
nl80211_vendor_cmds() so that it could take the RTNL and wiphy lock in the
correct order. Is that something you'd be open to Johannes?
Not very, to be honest. If we had a good use case for it, maybe, but
you're not even saying quite what the use case is :)
I believe Will and I are up against the same issues. Out-of-tree Android
drivers use a large number of vendor commands to support the
requirements of the Android framework. Prior to 5.12 these vendor
commands would always be called with the rtnl lock held, and in some
cases the implementation of the vendor commands care about that,
especially when calling back into the kernel. In particular we are faced
with the issue that there are some kernel APIs that require that the
rtnl lock be held, and as a result of the lock infrastructure change we
can no longer call those APIs from vendor commands. That is a pretty
severe limitation to work around.
I'm not really sure how sympathetic I am to an out-of-tree use case I
cannot even see, and I'd probably consider problematic in the first
place :)
You can see them, they're open source, just not in-tree.
That doesn't mean you wouldn't find things there problematic.
There are many reasons that most (all?) Android wifi drivers are
out-of-tree, but that is a different discussion.
Your easiest option might be to just patch NL80211_FLAG_NEED_RTNL into
your kernel for vendor commands and call it a day?
Well it isn't my kernel, it's Android's kernel since now with the ACK
they control the kernel:
https://source.android.com/devices/architecture/kernel/android-common
So Will and I would have to advocate for that, and this may be a
reasonable short-term solution. But I'm sure that Greg KH would like to
minimize the deltas between the ACK and upstream.
/jeff
