linux-kernel - [PATCH 13/14] kcm: replace call_rcu by kfree_rcu for simple kmem_cache

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Message-Id: <20240609082726.32742-14-Julia.Lawall@inria.fr>
Date: Sun,  9 Jun 2024 10:27:25 +0200
From: Julia Lawall <Julia.Lawall@...ia.fr>
To: "David S. Miller" <davem@...emloft.net>
Cc: kernel-janitors@...r.kernel.org,
	Eric Dumazet <edumazet@...gle.com>,
	Jakub Kicinski <kuba@...nel.org>,
	Paolo Abeni <pabeni@...hat.com>,
	netdev@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	"Paul E . McKenney" <paulmck@...nel.org>,
	Vlastimil Babka <vbabka@...e.cz>
Subject: [PATCH 13/14] kcm: 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>

---
 net/kcm/kcmsock.c |   10 +---------
 1 file changed, 1 insertion(+), 9 deletions(-)

diff --git a/net/kcm/kcmsock.c b/net/kcm/kcmsock.c
index 2f191e50d4fc..fbb730cd2d38 100644
--- a/net/kcm/kcmsock.c
+++ b/net/kcm/kcmsock.c
@@ -1580,14 +1580,6 @@ static int kcm_ioctl(struct socket *sock, unsigned int cmd, unsigned long arg)
 	return err;
 }
 
-static void free_mux(struct rcu_head *rcu)
-{
-	struct kcm_mux *mux = container_of(rcu,
-	    struct kcm_mux, rcu);
-
-	kmem_cache_free(kcm_muxp, mux);
-}
-
 static void release_mux(struct kcm_mux *mux)
 {
 	struct kcm_net *knet = mux->knet;
@@ -1615,7 +1607,7 @@ static void release_mux(struct kcm_mux *mux)
 	knet->count--;
 	mutex_unlock(&knet->mutex);
 
-	call_rcu(&mux->rcu, free_mux);
+	kfree_rcu(mux, rcu);
 }
 
 static void kcm_done(struct kcm_sock *kcm)