netdev - Re: [PATCH iwl-net] e1000: Move cancel_work

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Message-ID: <20250530183140.6cfad3ae@kernel.org>
Date: Fri, 30 May 2025 18:31:40 -0700
From: Jakub Kicinski <kuba@...nel.org>
To: Joe Damato <jdamato@...tly.com>
Cc: Stanislav Fomichev <stfomichev@...il.com>, netdev@...r.kernel.org,
 john.cs.hey@...il.com, jacob.e.keller@...el.com,
 syzbot+846bb38dc67fe62cc733@...kaller.appspotmail.com, Tony Nguyen
 <anthony.l.nguyen@...el.com>, Przemek Kitszel
 <przemyslaw.kitszel@...el.com>, Andrew Lunn <andrew+netdev@...n.ch>, "David
 S. Miller" <davem@...emloft.net>, Eric Dumazet <edumazet@...gle.com>, Paolo
 Abeni <pabeni@...hat.com>, "moderated list:INTEL ETHERNET DRIVERS"
 <intel-wired-lan@...ts.osuosl.org>, open list
 <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH iwl-net] e1000: Move cancel_work_sync to avoid deadlock

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