Re: [PATCH] nfsd: don't use GFP_KERNEL from nfsd_getxattr()/nfsd_listxattr()

[Jeff Layton <jlayton@kernel.org>]

On Sun, 2023-04-16 at 02:11 +0900, Tetsuo Handa wrote:
> On 2023/04/16 1:13, Chuck Lever III wrote:
> > > On Apr 15, 2023, at 7:07 AM, Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp> wrote:
> > > 
> > > Since GFP_KERNEL is GFP_NOFS | __GFP_FS, usage like GFP_KERNEL | GFP_NOFS
> > > does not make sense. Drop __GFP_FS flag in order to avoid deadlock.
> > 
> > The server side threads run in process context. GFP_KERNEL
> > is safe to use here -- as Jeff said, this code is not in
> > the server's reclaim path. Plenty of other call sites in
> > the NFS server code use GFP_KERNEL.
> 
> GFP_KERNEL memory allocation calls filesystem's shrinker functions
> because of __GFP_FS flag. My understanding is
> 
>   Whether this code is in memory reclaim path or not is irrelevant.
>   Whether memory reclaim path might hold lock or not is relevant.
> 
> . Therefore, question is, does nfsd hold i_rwsem during memory reclaim path?
> 

No. At the time of these allocations, the i_rwsem is not held.

> > 
> > But I agree that the flag combination doesn't make sense.
> > Maybe drop GFP_NOFS instead and call it only a clean-up?
> 

Yeah, I think that's the right thing to do here.

-- 
Jeff Layton <jlayton@kernel.org>