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Message-ID: <ZmrfA1p2zSVIaYam@zx2c4.com>
Date: Thu, 13 Jun 2024 13:58:59 +0200
From: "Jason A. Donenfeld" <Jason@...c4.com>
To: "Paul E. McKenney" <paulmck@...nel.org>
Cc: Jakub Kicinski <kuba@...nel.org>, Julia Lawall <Julia.Lawall@...ia.fr>,
linux-block@...r.kernel.org, kernel-janitors@...r.kernel.org,
bridge@...ts.linux.dev, linux-trace-kernel@...r.kernel.org,
Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
kvm@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org,
"Naveen N. Rao" <naveen.n.rao@...ux.ibm.com>,
Christophe Leroy <christophe.leroy@...roup.eu>,
Nicholas Piggin <npiggin@...il.com>, netdev@...r.kernel.org,
wireguard@...ts.zx2c4.com, linux-kernel@...r.kernel.org,
ecryptfs@...r.kernel.org, Neil Brown <neilb@...e.de>,
Olga Kornievskaia <kolga@...app.com>, Dai Ngo <Dai.Ngo@...cle.com>,
Tom Talpey <tom@...pey.com>, linux-nfs@...r.kernel.org,
linux-can@...r.kernel.org, Lai Jiangshan <jiangshanlai@...il.com>,
netfilter-devel@...r.kernel.org, coreteam@...filter.org,
Vlastimil Babka <vbabka@...e.cz>
Subject: Re: [PATCH 00/14] replace call_rcu by kfree_rcu for simple
kmem_cache_free callback
On Wed, Jun 12, 2024 at 03:37:55PM -0700, Paul E. McKenney wrote:
> On Wed, Jun 12, 2024 at 02:33:05PM -0700, Jakub Kicinski wrote:
> > On Sun, 9 Jun 2024 10:27:12 +0200 Julia Lawall wrote:
> > > 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.
> >
> > How does the discussion on:
> > [PATCH] Revert "batman-adv: prefer kfree_rcu() over call_rcu() with free-only callbacks"
> > https://lore.kernel.org/all/20240612133357.2596-1-linus.luessing@c0d3.blue/
> > reflect on this series? IIUC we should hold off..
>
> We do need to hold off for the ones in kernel modules (such as 07/14)
> where the kmem_cache is destroyed during module unload.
>
> OK, I might as well go through them...
>
> [PATCH 01/14] wireguard: allowedips: replace call_rcu by kfree_rcu for simple kmem_cache_free callback
> Needs to wait, see wg_allowedips_slab_uninit().
Also, notably, this patch needs additionally:
diff --git a/drivers/net/wireguard/allowedips.c b/drivers/net/wireguard/allowedips.c
index e4e1638fce1b..c95f6937c3f1 100644
--- a/drivers/net/wireguard/allowedips.c
+++ b/drivers/net/wireguard/allowedips.c
@@ -377,7 +377,6 @@ int __init wg_allowedips_slab_init(void)
void wg_allowedips_slab_uninit(void)
{
- rcu_barrier();
kmem_cache_destroy(node_cache);
}
Once kmem_cache_destroy has been fixed to be deferrable.
I assume the other patches are similar -- an rcu_barrier() can be
removed. So some manual meddling of these might be in order.
Jason
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