Re: [PATCH 2/5] net: Make rtnetlink infrastructure network namespace aware

Eric W. Biederman wrote:

Patrick McHardy [off-list ref] writes:

quoted

Maybe I can save you some time: we used to do down_trylock()
for the rtnl mutex, so senders would simply return if someone
else was already processing the queue *or* the rtnl was locked
for some other reason. In the first case the process already
processing the queue would also process the new messages, but
if it the rtnl was locked for some other reason (for example
during module registration) the message would sit in the
queue until the next rtnetlink sendmsg call, which is why
rtnl_unlock does queue processing. Commit 6756ae4b changed
the down_trylock to mutex_lock, so senders will now simply wait
until the mutex is released and then call netlink_run_queue
themselves. This means its not needed anymore.

Sounds reasonable.

I started looking through the code paths and I currently cannot
see anything that would leave a message on a kernel rtnl socket.

However I did a quick test adding a WARN_ON if there were any messages
found in the queue during rtnl_unlock and I found this code path
getting invoked from linkwatch_event.  So there is clearly something I
don't understand, and it sounds at odds just a bit from your
description.

That sounds like a bug. Did you place the WARN_ON before or after
the mutex_unlock()?