linux-kernel - [PATCH 09/14] block: replace call_rcu by kfree_rcu for simple kmem_cache

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Date: Sun,  9 Jun 2024 10:27:21 +0200
From: Julia Lawall <Julia.Lawall@...ia.fr>
To: Jens Axboe <axboe@...nel.dk>
Cc: kernel-janitors@...r.kernel.org,
	linux-block@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	"Paul E . McKenney" <paulmck@...nel.org>,
	Vlastimil Babka <vbabka@...e.cz>
Subject: [PATCH 09/14] block: 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>

---
 block/blk-ioc.c |    9 +--------
 1 file changed, 1 insertion(+), 8 deletions(-)

diff --git a/block/blk-ioc.c b/block/blk-ioc.c
index 25dd4db11121..ce82770c72ab 100644
--- a/block/blk-ioc.c
+++ b/block/blk-ioc.c
@@ -32,13 +32,6 @@ static void get_io_context(struct io_context *ioc)
 	atomic_long_inc(&ioc->refcount);
 }
 
-static void icq_free_icq_rcu(struct rcu_head *head)
-{
-	struct io_cq *icq = container_of(head, struct io_cq, __rcu_head);
-
-	kmem_cache_free(icq->__rcu_icq_cache, icq);
-}
-
 /*
  * Exit an icq. Called with ioc locked for blk-mq, and with both ioc
  * and queue locked for legacy.
@@ -102,7 +95,7 @@ static void ioc_destroy_icq(struct io_cq *icq)
 	 */
 	icq->__rcu_icq_cache = et->icq_cache;
 	icq->flags |= ICQ_DESTROYED;
-	call_rcu(&icq->__rcu_head, icq_free_icq_rcu);
+	kfree_rcu(icq, __rcu_head);
 }
 
 /*