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

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Date: Mon, 10 Jun 2024 22:42:30 +0200
From: Vlastimil Babka <vbabka@...e.cz>
To: paulmck@...nel.org, Steven Rostedt <rostedt@...dmis.org>
Cc: Julia Lawall <Julia.Lawall@...ia.fr>, 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
Subject: Re: [PATCH 05/14] tracefs: replace call_rcu by kfree_rcu for simple
 kmem_cache_free callback

On 6/10/24 5:46 PM, Paul E. McKenney wrote:
> On Mon, Jun 10, 2024 at 11:22:23AM -0400, Steven Rostedt wrote:
>> On Sun,  9 Jun 2024 10:27:17 +0200
>> Julia Lawall <Julia.Lawall@...ia.fr> wrote:
>> 
>> > 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);
>> 
>> Does this work?
>> 
>> tracefs needs to be freed via the tracefs_inode_cachep. Does
>> kfree_rcu() handle specific frees for objects that were not allocated
>> via kmalloc()?
> 
> A recent change to kfree() allows it to correctly handle memory allocated
> via kmem_cache_alloc().  News to me as of a few weeks ago.  ;-)

Hey, I did try not to keep that a secret :)
https://lore.kernel.org/all/20230310103210.22372-8-vbabka@suse.cz/

> 							Thanx, Paul
> 
>> -- Steve
>> 
>> 
>> > -}
>> > -
>> >  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,
>>