linux-kernel - Re: [PATCH 00/14] replace call_rcu by kfree_rcu for simple kmem_cache

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Message-ID: <1585a3fc-ade2-4e1e-a016-e04336c0a103@suse.cz>
Date: Tue, 8 Oct 2024 18:36:10 +0200
From: Vlastimil Babka <vbabka@...e.cz>
To: Julia Lawall <Julia.Lawall@...ia.fr>, linux-block@...r.kernel.org
Cc: 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,
 "Paul E . McKenney" <paulmck@...nel.org>,
 "Uladzislau Rezki (Sony)" <urezki@...il.com>,
 "Jason A. Donenfeld" <Jason@...c4.com>, Steven Rostedt <rostedt@...dmis.org>
Subject: Re: [PATCH 00/14] replace call_rcu by kfree_rcu for simple
 kmem_cache_free callback

On 6/9/24 10:27, 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.

FYI, as of 6.12-rc1 - commit 6c6c47b063b5 ("mm, slab: call
kvfree_rcu_barrier() from kmem_cache_destroy()")
it should be possible to restart this effort for the remaining cases which
had to be postponed until kmem_cache_destroy() / module unload is sorted out.

Thanks,
Vlastimil

> 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>
> 
> ---
> 
>  arch/powerpc/kvm/book3s_mmu_hpte.c  |    8 +-------
>  block/blk-ioc.c                     |    9 +--------
>  drivers/net/wireguard/allowedips.c  |    9 ++-------
>  fs/ecryptfs/dentry.c                |    8 +-------
>  fs/nfsd/nfs4state.c                 |    9 +--------
>  fs/tracefs/inode.c                  |   10 +---------
>  kernel/time/posix-timers.c          |    9 +--------
>  kernel/workqueue.c                  |    8 +-------
>  net/bridge/br_fdb.c                 |    9 +--------
>  net/can/gw.c                        |   13 +++----------
>  net/ipv4/fib_trie.c                 |    8 +-------
>  net/ipv4/inetpeer.c                 |    9 ++-------
>  net/ipv6/ip6_fib.c                  |    9 +--------
>  net/ipv6/xfrm6_tunnel.c             |    8 +-------
>  net/kcm/kcmsock.c                   |   10 +---------
>  net/netfilter/nf_conncount.c        |   10 +---------
>  net/netfilter/nf_conntrack_expect.c |   10 +---------
>  net/netfilter/xt_hashlimit.c        |    9 +--------
>  18 files changed, 22 insertions(+), 143 deletions(-)