Re: [PATCH iwl-net] e1000: Move cancel_work_sync to avoid deadlock

[Jakub Kicinski <kuba@kernel.org>]

On Fri, 30 May 2025 12:45:13 -0700 Joe Damato wrote:
> > nit: as Jakub mentioned in another thread, it seems more about the
> > flush_work waiting for the reset_task to complete rather than
> > wq mutexes (which are fake)?  
> 
> Hm, I probably misunderstood something. Also, not sure what you
> meant by the wq mutexes being fake?
> 
> My understanding (which is prob wrong) from the syzbot and user
> report was that the order of wq mutex and rtnl are inverted in the
> two paths, which can cause a deadlock if both paths run.

Take a look at touch_work_lockdep_map(), theres nosaj thing as wq mutex.
It's just a lockdep "annotation" that helps lockdep connect the dots
between waiting thread and the work item, not a real mutex. So the
commit msg may be better phrased like this (modulo the lines in front):

   CPU 0:
  , - RTNL is held
 /  - e1000_close
 |  - e1000_down
 +- - cancel_work_sync (cancel / wait for e1000_reset_task())
 |
 | CPU 1:
 |  - process_one_work
  \ - e1000_reset_task
   `- take RTNL