[06/17] batman-adv: replace call_rcu by kfree_rcu for simple kmem_cache_free callback

  Since SLOB was removed and since
commit 6c6c47b063b5 ("mm, slab: call kvfree_rcu_barrier() from kmem_cache_destroy()"),
it is not necessary to use call_rcu when the callback only performs
kmem_cache_free. Use kfree_rcu() directly.

The changes were made using Coccinelle.

Signed-off-by: Julia Lawall <Julia.Lawall@inria.fr>

---
 net/batman-adv/translation-table.c |   47 ++-----------------------------------
 1 file changed, 3 insertions(+), 44 deletions(-)
  

On Sunday, 13 October 2024 22:16:53 CEST Julia Lawall wrote:
> Since SLOB was removed and since
> commit 6c6c47b063b5 ("mm, slab: call kvfree_rcu_barrier() from kmem_cache_destroy()"),
> it is not necessary to use call_rcu when the callback only performs
> kmem_cache_free. Use kfree_rcu() directly.
> 
> The changes were made using Coccinelle.
> 
> Signed-off-by: Julia Lawall <Julia.Lawall@inria.fr>
> 
> ---
>  net/batman-adv/translation-table.c |   47 ++-----------------------------------
>  1 file changed, 3 insertions(+), 44 deletions(-)


This was tried and we noticed that it is not safe [1]. So, I would get 
confirmation that commit 6c6c47b063b5 ("mm, slab: call kvfree_rcu_barrier() 
from kmem_cache_destroy()") is fixing the problem which we had at that time. 
The commit message sounds like it but I just want to be sure.

Kind regards,
	Sven

[1] https://lore.kernel.org/r/20240612133357.2596-1-linus.luessing@c0d3.blue

> 
> diff --git a/net/batman-adv/translation-table.c b/net/batman-adv/translation-table.c
> index 2243cec18ecc..b21ff3c36b07 100644
> --- a/net/batman-adv/translation-table.c
> +++ b/net/batman-adv/translation-table.c
> @@ -208,20 +208,6 @@ batadv_tt_global_hash_find(struct batadv_priv *bat_priv, const u8 *addr,
>  	return tt_global_entry;
>  }
>  
> -/**
> - * batadv_tt_local_entry_free_rcu() - free the tt_local_entry
> - * @rcu: rcu pointer of the tt_local_entry
> - */
> -static void batadv_tt_local_entry_free_rcu(struct rcu_head *rcu)
> -{
> -	struct batadv_tt_local_entry *tt_local_entry;
> -
> -	tt_local_entry = container_of(rcu, struct batadv_tt_local_entry,
> -				      common.rcu);
> -
> -	kmem_cache_free(batadv_tl_cache, tt_local_entry);
> -}
> -
>  /**
>   * batadv_tt_local_entry_release() - release tt_local_entry from lists and queue
>   *  for free after rcu grace period
> @@ -236,7 +222,7 @@ static void batadv_tt_local_entry_release(struct kref *ref)
>  
>  	batadv_softif_vlan_put(tt_local_entry->vlan);
>  
> -	call_rcu(&tt_local_entry->common.rcu, batadv_tt_local_entry_free_rcu);
> +	kfree_rcu(tt_local_entry, common.rcu);
>  }
>  
>  /**
> @@ -254,20 +240,6 @@ batadv_tt_local_entry_put(struct batadv_tt_local_entry *tt_local_entry)
>  		 batadv_tt_local_entry_release);
>  }
>  
> -/**
> - * batadv_tt_global_entry_free_rcu() - free the tt_global_entry
> - * @rcu: rcu pointer of the tt_global_entry
> - */
> -static void batadv_tt_global_entry_free_rcu(struct rcu_head *rcu)
> -{
> -	struct batadv_tt_global_entry *tt_global_entry;
> -
> -	tt_global_entry = container_of(rcu, struct batadv_tt_global_entry,
> -				       common.rcu);
> -
> -	kmem_cache_free(batadv_tg_cache, tt_global_entry);
> -}
> -
>  /**
>   * batadv_tt_global_entry_release() - release tt_global_entry from lists and
>   *  queue for free after rcu grace period
> @@ -282,7 +254,7 @@ void batadv_tt_global_entry_release(struct kref *ref)
>  
>  	batadv_tt_global_del_orig_list(tt_global_entry);
>  
> -	call_rcu(&tt_global_entry->common.rcu, batadv_tt_global_entry_free_rcu);
> +	kfree_rcu(tt_global_entry, common.rcu);
>  }
>  
>  /**
> @@ -407,19 +379,6 @@ static void batadv_tt_global_size_dec(struct batadv_orig_node *orig_node,
>  	batadv_tt_global_size_mod(orig_node, vid, -1);
>  }
>  
> -/**
> - * batadv_tt_orig_list_entry_free_rcu() - free the orig_entry
> - * @rcu: rcu pointer of the orig_entry
> - */
> -static void batadv_tt_orig_list_entry_free_rcu(struct rcu_head *rcu)
> -{
> -	struct batadv_tt_orig_list_entry *orig_entry;
> -
> -	orig_entry = container_of(rcu, struct batadv_tt_orig_list_entry, rcu);
> -
> -	kmem_cache_free(batadv_tt_orig_cache, orig_entry);
> -}
> -
>  /**
>   * batadv_tt_orig_list_entry_release() - release tt orig entry from lists and
>   *  queue for free after rcu grace period
> @@ -433,7 +392,7 @@ static void batadv_tt_orig_list_entry_release(struct kref *ref)
>  				  refcount);
>  
>  	batadv_orig_node_put(orig_entry->orig_node);
> -	call_rcu(&orig_entry->rcu, batadv_tt_orig_list_entry_free_rcu);
> +	kfree_rcu(orig_entry, rcu);
>  }
>  
>  /**
> 
>
  

On Mon, 14 Oct 2024, Sven Eckelmann wrote:

> On Sunday, 13 October 2024 22:16:53 CEST Julia Lawall wrote:
> > Since SLOB was removed and since
> > commit 6c6c47b063b5 ("mm, slab: call kvfree_rcu_barrier() from kmem_cache_destroy()"),
> > it is not necessary to use call_rcu when the callback only performs
> > kmem_cache_free. Use kfree_rcu() directly.
> >
> > The changes were made using Coccinelle.
> >
> > Signed-off-by: Julia Lawall <Julia.Lawall@inria.fr>
> >
> > ---
> >  net/batman-adv/translation-table.c |   47 ++-----------------------------------
> >  1 file changed, 3 insertions(+), 44 deletions(-)
>
>
> This was tried and we noticed that it is not safe [1]. So, I would get
> confirmation that commit 6c6c47b063b5 ("mm, slab: call kvfree_rcu_barrier()
> from kmem_cache_destroy()") is fixing the problem which we had at that time.
> The commit message sounds like it but I just want to be sure.

Thanks for the feedback. I think that Vlastimil Babka can help with that.

julia

>
> Kind regards,
> 	Sven
>
> [1] https://lore.kernel.org/r/20240612133357.2596-1-linus.luessing@c0d3.blue
>
> >
> > diff --git a/net/batman-adv/translation-table.c b/net/batman-adv/translation-table.c
> > index 2243cec18ecc..b21ff3c36b07 100644
> > --- a/net/batman-adv/translation-table.c
> > +++ b/net/batman-adv/translation-table.c
> > @@ -208,20 +208,6 @@ batadv_tt_global_hash_find(struct batadv_priv *bat_priv, const u8 *addr,
> >  	return tt_global_entry;
> >  }
> >
> > -/**
> > - * batadv_tt_local_entry_free_rcu() - free the tt_local_entry
> > - * @rcu: rcu pointer of the tt_local_entry
> > - */
> > -static void batadv_tt_local_entry_free_rcu(struct rcu_head *rcu)
> > -{
> > -	struct batadv_tt_local_entry *tt_local_entry;
> > -
> > -	tt_local_entry = container_of(rcu, struct batadv_tt_local_entry,
> > -				      common.rcu);
> > -
> > -	kmem_cache_free(batadv_tl_cache, tt_local_entry);
> > -}
> > -
> >  /**
> >   * batadv_tt_local_entry_release() - release tt_local_entry from lists and queue
> >   *  for free after rcu grace period
> > @@ -236,7 +222,7 @@ static void batadv_tt_local_entry_release(struct kref *ref)
> >
> >  	batadv_softif_vlan_put(tt_local_entry->vlan);
> >
> > -	call_rcu(&tt_local_entry->common.rcu, batadv_tt_local_entry_free_rcu);
> > +	kfree_rcu(tt_local_entry, common.rcu);
> >  }
> >
> >  /**
> > @@ -254,20 +240,6 @@ batadv_tt_local_entry_put(struct batadv_tt_local_entry *tt_local_entry)
> >  		 batadv_tt_local_entry_release);
> >  }
> >
> > -/**
> > - * batadv_tt_global_entry_free_rcu() - free the tt_global_entry
> > - * @rcu: rcu pointer of the tt_global_entry
> > - */
> > -static void batadv_tt_global_entry_free_rcu(struct rcu_head *rcu)
> > -{
> > -	struct batadv_tt_global_entry *tt_global_entry;
> > -
> > -	tt_global_entry = container_of(rcu, struct batadv_tt_global_entry,
> > -				       common.rcu);
> > -
> > -	kmem_cache_free(batadv_tg_cache, tt_global_entry);
> > -}
> > -
> >  /**
> >   * batadv_tt_global_entry_release() - release tt_global_entry from lists and
> >   *  queue for free after rcu grace period
> > @@ -282,7 +254,7 @@ void batadv_tt_global_entry_release(struct kref *ref)
> >
> >  	batadv_tt_global_del_orig_list(tt_global_entry);
> >
> > -	call_rcu(&tt_global_entry->common.rcu, batadv_tt_global_entry_free_rcu);
> > +	kfree_rcu(tt_global_entry, common.rcu);
> >  }
> >
> >  /**
> > @@ -407,19 +379,6 @@ static void batadv_tt_global_size_dec(struct batadv_orig_node *orig_node,
> >  	batadv_tt_global_size_mod(orig_node, vid, -1);
> >  }
> >
> > -/**
> > - * batadv_tt_orig_list_entry_free_rcu() - free the orig_entry
> > - * @rcu: rcu pointer of the orig_entry
> > - */
> > -static void batadv_tt_orig_list_entry_free_rcu(struct rcu_head *rcu)
> > -{
> > -	struct batadv_tt_orig_list_entry *orig_entry;
> > -
> > -	orig_entry = container_of(rcu, struct batadv_tt_orig_list_entry, rcu);
> > -
> > -	kmem_cache_free(batadv_tt_orig_cache, orig_entry);
> > -}
> > -
> >  /**
> >   * batadv_tt_orig_list_entry_release() - release tt orig entry from lists and
> >   *  queue for free after rcu grace period
> > @@ -433,7 +392,7 @@ static void batadv_tt_orig_list_entry_release(struct kref *ref)
> >  				  refcount);
> >
> >  	batadv_orig_node_put(orig_entry->orig_node);
> > -	call_rcu(&orig_entry->rcu, batadv_tt_orig_list_entry_free_rcu);
> > +	kfree_rcu(orig_entry, rcu);
> >  }
> >
> >  /**
> >
> >
>
>
  

On 10/14/24 09:08, Julia Lawall wrote:
> 
> 
> On Mon, 14 Oct 2024, Sven Eckelmann wrote:
> 
>> On Sunday, 13 October 2024 22:16:53 CEST Julia Lawall wrote:
>> > Since SLOB was removed and since
>> > commit 6c6c47b063b5 ("mm, slab: call kvfree_rcu_barrier() from kmem_cache_destroy()"),
>> > it is not necessary to use call_rcu when the callback only performs
>> > kmem_cache_free. Use kfree_rcu() directly.
>> >
>> > The changes were made using Coccinelle.
>> >
>> > Signed-off-by: Julia Lawall <Julia.Lawall@inria.fr>
>> >
>> > ---
>> >  net/batman-adv/translation-table.c |   47 ++-----------------------------------
>> >  1 file changed, 3 insertions(+), 44 deletions(-)
>>
>>
>> This was tried and we noticed that it is not safe [1]. So, I would get
>> confirmation that commit 6c6c47b063b5 ("mm, slab: call kvfree_rcu_barrier()
>> from kmem_cache_destroy()") is fixing the problem which we had at that time.
>> The commit message sounds like it but I just want to be sure.
> 
> Thanks for the feedback. I think that Vlastimil Babka can help with that.

Hi, yeah the batman-adv issue was how we learned about the problem and the
series of commits leading to and including 6c6c47b063b5 was done exactly to
address the kmem_cache_destroy() on module unload issue, and unblock the
conversion to kfree_rcu().

Thanks, Vlastimil

> julia
  

On Sun, 13 Oct 2024 22:16:53 +0200, Julia Lawall wrote:
> Since SLOB was removed and since
> commit 6c6c47b063b5 ("mm, slab: call kvfree_rcu_barrier() from kmem_cache_destroy()"),
> it is not necessary to use call_rcu when the callback only performs
> kmem_cache_free. Use kfree_rcu() directly.
> 
> The changes were made using Coccinelle.
> 
> [...]

Applied, thanks!

[06/17] batman-adv: replace call_rcu by kfree_rcu for simple kmem_cache_free callback
        commit: 356c81b6c494a359ed6e25087931acc78c518fb9

Best regards,