linux-kernel - Re: [PATCH] nfsd: validate the nfsd_serv pointer before calling svc_wake

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Message-id: <173818520688.22054.4135013466624893151@noble.neil.brown.name>
Date: Thu, 30 Jan 2025 08:13:26 +1100
From: "NeilBrown" <neilb@...e.de>
To: cel@...nel.org
Cc: "Olga Kornievskaia" <okorniev@...hat.com>, "Dai Ngo" <Dai.Ngo@...cle.com>,
 "Tom Talpey" <tom@...pey.com>, "Jeff Layton" <jlayton@...nel.org>,
 "Chuck Lever" <chuck.lever@...cle.com>,
 "Salvatore Bonaccorso" <carnil@...ian.org>, linux-nfs@...r.kernel.org,
 linux-kernel@...r.kernel.org
Subject:
 Re: [PATCH] nfsd: validate the nfsd_serv pointer before calling svc_wake_up

On Wed, 29 Jan 2025, cel@...nel.org wrote:
> From: Chuck Lever <chuck.lever@...cle.com>
> 
> On Sat, 25 Jan 2025 20:13:18 -0500, Jeff Layton wrote:
> > nfsd_file_dispose_list_delayed can be called from the filecache
> > laundrette, which is shut down after the nfsd threads are shut down and
> > the nfsd_serv pointer is cleared. If nn->nfsd_serv is NULL then there
> > are no threads to wake.
> > 
> > Ensure that the nn->nfsd_serv pointer is non-NULL before calling
> > svc_wake_up in nfsd_file_dispose_list_delayed. This is safe since the
> > svc_serv is not freed until after the filecache laundrette is cancelled.
> > 
> > [...]
> 
> Applied to nfsd-testing, thanks!
> 
> Test experience should demonstrate whether more strict memory
> ordering semantics are needed.

No it won't.  The need for READ_ONCE is theoretical, not - in this case
- practical.

“Program testing can be used to show the presence of bugs, but never to show their absence!”
― Edsger W. Dijkstra 

NeilBrown

> 
> [1/1] nfsd: validate the nfsd_serv pointer before calling svc_wake_up
>       commit: 363683ced1718d66ad54e1bdf52d41d544f783b2
> 
> --
> Chuck Lever
> 
>