linux-kernel - Re: [PATCH 08/14] nfsd: replace call_rcu by kfree_rcu for simple kmem_cache

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Date: Sun, 09 Jun 2024 06:53:20 -0400
From: Jeff Layton <jlayton@...nel.org>
To: Julia Lawall <Julia.Lawall@...ia.fr>, Chuck Lever
 <chuck.lever@...cle.com>
Cc: kernel-janitors@...r.kernel.org, Neil Brown <neilb@...e.de>, Olga
 Kornievskaia <kolga@...app.com>, Dai Ngo <Dai.Ngo@...cle.com>, Tom Talpey
 <tom@...pey.com>,  linux-nfs@...r.kernel.org, linux-kernel@...r.kernel.org,
 "Paul E . McKenney" <paulmck@...nel.org>, Vlastimil Babka <vbabka@...e.cz>
Subject: Re: [PATCH 08/14] nfsd: replace call_rcu by kfree_rcu for simple
 kmem_cache_free callback

On Sun, 2024-06-09 at 10:27 +0200, Julia Lawall wrote:
> Since SLOB was removed, it is not necessary to use call_rcu
> when the callback only performs kmem_cache_free. Use
> kfree_rcu() directly.
> 
> The changes were done using the following Coccinelle semantic patch.
> This semantic patch is designed to ignore cases where the callback
> function is used in another way.
> 
> // <smpl>
> @r@
> expression e;
> local idexpression e2;
> identifier cb,f;
> position p;
> @@
> 
> (
> call_rcu(...,e2)
> > 
> call_rcu(&e->f,cb@p)
> )
> 
> @r1@
> type T;
> identifier x,r.cb;
> @@
> 
>  cb(...) {
> (
>    kmem_cache_free(...);
> > 
>    T x = ...;
>    kmem_cache_free(...,x);
> > 
>    T x;
>    x = ...;
>    kmem_cache_free(...,x);
> )
>  }
> 
> @s depends on r1@
> position p != r.p;
> identifier r.cb;
> @@
> 
>  cb@p
> 
> @script:ocaml@
> cb << r.cb;
> p << s.p;
> @@
> 
> Printf.eprintf "Other use of %s at %s:%d\n"
>    cb (List.hd p).file (List.hd p).line
> 
> @depends on r1 && !s@
> expression e;
> identifier r.cb,f;
> position r.p;
> @@
> 
> - call_rcu(&e->f,cb@p)
> + kfree_rcu(e,f)
> 
> @r1a depends on !s@
> type T;
> identifier x,r.cb;
> @@
> 
> - cb(...) {
> (
> -  kmem_cache_free(...);
> > 
> -  T x = ...;
> -  kmem_cache_free(...,x);
> > 
> -  T x;
> -  x = ...;
> -  kmem_cache_free(...,x);
> )
> - }
> // </smpl>
> 
> Signed-off-by: Julia Lawall <Julia.Lawall@...ia.fr>
> Reviewed-by: Paul E. McKenney <paulmck@...nel.org>
> Reviewed-by: Vlastimil Babka <vbabka@...e.cz>
> 
> ---
>  fs/nfsd/nfs4state.c |    9 +--------
>  1 file changed, 1 insertion(+), 8 deletions(-)
> 
> diff --git a/fs/nfsd/nfs4state.c b/fs/nfsd/nfs4state.c
> index a20c2c9d7d45..eba5083504c7 100644
> --- a/fs/nfsd/nfs4state.c
> +++ b/fs/nfsd/nfs4state.c
> @@ -571,13 +571,6 @@ opaque_hashval(const void *ptr, int nbytes)
>  	return x;
>  }
>  
> -static void nfsd4_free_file_rcu(struct rcu_head *rcu)
> -{
> -	struct nfs4_file *fp = container_of(rcu, struct nfs4_file, fi_rcu);
> -
> -	kmem_cache_free(file_slab, fp);
> -}
> -
>  void
>  put_nfs4_file(struct nfs4_file *fi)
>  {
> @@ -585,7 +578,7 @@ put_nfs4_file(struct nfs4_file *fi)
>  		nfsd4_file_hash_remove(fi);
>  		WARN_ON_ONCE(!list_empty(&fi->fi_clnt_odstate));
>  		WARN_ON_ONCE(!list_empty(&fi->fi_delegations));
> -		call_rcu(&fi->fi_rcu, nfsd4_free_file_rcu);
> +		kfree_rcu(fi, fi_rcu);
>  	}
>  }
>  
> 

Reviewed-by: Jeff Layton <jlayton@...nel.org>