netdev - Re: [syzbot] [net?] possible deadlock in rtnl

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Message-ID: <aDjzpDHwcFuGhAqp@LQ3V64L9R2>
Date: Thu, 29 May 2025 16:54:12 -0700
From: Joe Damato <jdamato@...tly.com>
To: Stanislav Fomichev <stfomichev@...il.com>
Cc: Jakub Kicinski <kuba@...nel.org>,
	syzbot <syzbot+846bb38dc67fe62cc733@...kaller.appspotmail.com>,
	davem@...emloft.net, edumazet@...gle.com, horms@...nel.org,
	linux-kernel@...r.kernel.org, netdev@...r.kernel.org,
	pabeni@...hat.com, syzkaller-bugs@...glegroups.com
Subject: Re: [syzbot] [net?] possible deadlock in rtnl_newlink

On Thu, May 29, 2025 at 09:45:10AM -0700, Stanislav Fomichev wrote:
> On 05/29, Jakub Kicinski wrote:
> > On Thu, 29 May 2025 08:59:43 -0700 Stanislav Fomichev wrote:
> > > So this is internal WQ entry lock that is being reordered with rtnl
> > > lock. But looking at process_one_work, I don't see actual locks, mostly
> > > lock_map_acquire/lock_map_release calls to enforce some internal WQ
> > > invariants. Not sure what to do with it, will try to read more.
> > 
> > Basically a flush_work() happens while holding rtnl_lock,
> > but the work itself takes that lock. It's a driver bug.
> 
> e400c7444d84 ("e1000: Hold RTNL when e1000_down can be called") ?
> I think similar things (but wrt netdev instance lock) are happening
> with iavf: iavf_remove calls cancel_work_sync while holding the
> instance lock and the work callbacks grab the instance lock as well :-/

I think this is probably the same thread as:

 https://lore.kernel.org/netdev/CAP=Rh=OEsn4y_2LvkO3UtDWurKcGPnZ_NPSXK=FbgygNXL37Sw@mail.gmail.com/

I posted a response there about how to possibly avoid the problem
(based on my rough reading of the driver code), but am still
thinking more on this.