linux-kernel - [PATCH 05/14] tracefs: replace call_rcu by kfree_rcu for simple kmem_cache

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Message-Id: <20240609082726.32742-6-Julia.Lawall@inria.fr>
Date: Sun,  9 Jun 2024 10:27:17 +0200
From: Julia Lawall <Julia.Lawall@...ia.fr>
To: Steven Rostedt <rostedt@...dmis.org>
Cc: kernel-janitors@...r.kernel.org,
	Masami Hiramatsu <mhiramat@...nel.org>,
	Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
	linux-kernel@...r.kernel.org,
	linux-trace-kernel@...r.kernel.org,
	"Paul E . McKenney" <paulmck@...nel.org>,
	Vlastimil Babka <vbabka@...e.cz>
Subject: [PATCH 05/14] tracefs: 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/tracefs/inode.c |   10 +---------
 1 file changed, 1 insertion(+), 9 deletions(-)

diff --git a/fs/tracefs/inode.c b/fs/tracefs/inode.c
index 7c29f4afc23d..338c52168e61 100644
--- a/fs/tracefs/inode.c
+++ b/fs/tracefs/inode.c
@@ -53,14 +53,6 @@ static struct inode *tracefs_alloc_inode(struct super_block *sb)
 	return &ti->vfs_inode;
 }
 
-static void tracefs_free_inode_rcu(struct rcu_head *rcu)
-{
-	struct tracefs_inode *ti;
-
-	ti = container_of(rcu, struct tracefs_inode, rcu);
-	kmem_cache_free(tracefs_inode_cachep, ti);
-}
-
 static void tracefs_free_inode(struct inode *inode)
 {
 	struct tracefs_inode *ti = get_tracefs(inode);
@@ -70,7 +62,7 @@ static void tracefs_free_inode(struct inode *inode)
 	list_del_rcu(&ti->list);
 	spin_unlock_irqrestore(&tracefs_inode_lock, flags);
 
-	call_rcu(&ti->rcu, tracefs_free_inode_rcu);
+	kfree_rcu(ti, rcu);
 }
 
 static ssize_t default_read_file(struct file *file, char __user *buf,