linux-kernel - Re: [PATCH 06/17] batman-adv: replace call_rcu by kfree_rcu for simple kmem_cache

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Message-ID: <f343355b-eda9-8527-ee2c-60f1e44e6e0@inria.fr>
Date: Mon, 14 Oct 2024 09:08:30 +0200 (CEST)
From: Julia Lawall <julia.lawall@...ia.fr>
To: Sven Eckelmann <sven@...fation.org>
cc: Julia Lawall <Julia.Lawall@...ia.fr>, vbabka@...e.cz, 
    linus.luessing@...3.blue, Marek Lindner <mareklindner@...mailbox.ch>, 
    kernel-janitors@...r.kernel.org, paulmck@...nel.org, 
    Simon Wunderlich <sw@...onwunderlich.de>, 
    Antonio Quartulli <a@...table.cc>, "David S. Miller" <davem@...emloft.net>, 
    Eric Dumazet <edumazet@...gle.com>, Jakub Kicinski <kuba@...nel.org>, 
    Paolo Abeni <pabeni@...hat.com>, b.a.t.m.a.n@...ts.open-mesh.org, 
    netdev@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 06/17] batman-adv: replace call_rcu by kfree_rcu for
 simple kmem_cache_free callback



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@...ia.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);
> >  }
> >
> >  /**
> >
> >
>
>