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

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Date: Sun,  9 Jun 2024 10:27:20 +0200
From: Julia Lawall <Julia.Lawall@...ia.fr>
To: Chuck Lever <chuck.lever@...cle.com>
Cc: kernel-janitors@...r.kernel.org,
	Jeff Layton <jlayton@...nel.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: [PATCH 08/14] nfsd: replace call_rcu by kfree_rcu for simple kmem_cache_free callback

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);
 	}
 }