linux-kernel - [PATCH 01/14] wireguard: allowedips: replace call_rcu by kfree_rcu for simple kmem_cache

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Date: Sun,  9 Jun 2024 10:27:13 +0200
From: Julia Lawall <Julia.Lawall@...ia.fr>
To: "Jason A. Donenfeld" <Jason@...c4.com>
Cc: kernel-janitors@...r.kernel.org,
	"David S. Miller" <davem@...emloft.net>,
	Eric Dumazet <edumazet@...gle.com>,
	Jakub Kicinski <kuba@...nel.org>,
	Paolo Abeni <pabeni@...hat.com>,
	wireguard@...ts.zx2c4.com,
	netdev@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	"Paul E . McKenney" <paulmck@...nel.org>,
	Vlastimil Babka <vbabka@...e.cz>
Subject: [PATCH 01/14] wireguard: allowedips: 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>

---
 drivers/net/wireguard/allowedips.c |    9 ++-------
 1 file changed, 2 insertions(+), 7 deletions(-)

diff --git a/drivers/net/wireguard/allowedips.c b/drivers/net/wireguard/allowedips.c
index 0ba714ca5185..e4e1638fce1b 100644
--- a/drivers/net/wireguard/allowedips.c
+++ b/drivers/net/wireguard/allowedips.c
@@ -48,11 +48,6 @@ static void push_rcu(struct allowedips_node **stack,
 	}
 }
 
-static void node_free_rcu(struct rcu_head *rcu)
-{
-	kmem_cache_free(node_cache, container_of(rcu, struct allowedips_node, rcu));
-}
-
 static void root_free_rcu(struct rcu_head *rcu)
 {
 	struct allowedips_node *node, *stack[MAX_ALLOWEDIPS_DEPTH] = {
@@ -330,13 +325,13 @@ void wg_allowedips_remove_by_peer(struct allowedips *table,
 			child = rcu_dereference_protected(
 					parent->bit[!(node->parent_bit_packed & 1)],
 					lockdep_is_held(lock));
-		call_rcu(&node->rcu, node_free_rcu);
+		kfree_rcu(node, rcu);
 		if (!free_parent)
 			continue;
 		if (child)
 			child->parent_bit_packed = parent->parent_bit_packed;
 		*(struct allowedips_node **)(parent->parent_bit_packed & ~3UL) = child;
-		call_rcu(&parent->rcu, node_free_rcu);
+		kfree_rcu(parent, rcu);
 	}
 }