Re: [PATCH 00/14] replace call_rcu by kfree_rcu for simple kmem_cache_free callback

[Vlastimil Babka <vbabka@suse.cz>]

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@inria.fr>
> Reviewed-by: Paul E. McKenney <paulmck@kernel.org>
> Reviewed-by: Vlastimil Babka <vbabka@suse.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(-)