linux-kernel - [PATCH 12/14] workqueue: replace call_rcu by kfree_rcu for simple kmem_cache

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Date: Sun,  9 Jun 2024 10:27:24 +0200
From: Julia Lawall <Julia.Lawall@...ia.fr>
To: Tejun Heo <tj@...nel.org>
Cc: kernel-janitors@...r.kernel.org,
	Lai Jiangshan <jiangshanlai@...il.com>,
	linux-kernel@...r.kernel.org,
	"Paul E . McKenney" <paulmck@...nel.org>,
	Vlastimil Babka <vbabka@...e.cz>
Subject: [PATCH 12/14] workqueue: 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>

---
 kernel/workqueue.c |    8 +-------
 1 file changed, 1 insertion(+), 7 deletions(-)

diff --git a/kernel/workqueue.c b/kernel/workqueue.c
index 3fbaecfc88c2..2ec195dcc2bb 100644
--- a/kernel/workqueue.c
+++ b/kernel/workqueue.c
@@ -5038,12 +5038,6 @@ static struct worker_pool *get_unbound_pool(const struct workqueue_attrs *attrs)
 	return NULL;
 }
 
-static void rcu_free_pwq(struct rcu_head *rcu)
-{
-	kmem_cache_free(pwq_cache,
-			container_of(rcu, struct pool_workqueue, rcu));
-}
-
 /*
  * Scheduled on pwq_release_worker by put_pwq() when an unbound pwq hits zero
  * refcnt and needs to be destroyed.
@@ -5089,7 +5083,7 @@ static void pwq_release_workfn(struct kthread_work *work)
 		raw_spin_unlock_irq(&nna->lock);
 	}
 
-	call_rcu(&pwq->rcu, rcu_free_pwq);
+	kfree_rcu(pwq, rcu);
 
 	/*
 	 * If we're the last pwq going away, @wq is already dead and no one