On Mon, May 27, 2024 at 10:43:08PM +0200, Julia Lawall wrote:
>
>
> On Mon, 27 May 2024, Paul E. McKenney wrote:
>
> > On Mon, May 27, 2024 at 10:13:40AM +0200, Julia Lawall wrote:
> > >
> > >
> > > On Mon, 27 May 2024, Vlastimil Babka wrote:
> > >
> > > > Hi,
> > > >
> > > > one bit from LSF/MM discussions is that there might be call_rcu users
> > > > with a
> > > > callback that only does a kmem_cache_free() to a specific cache. Since
> > > > SLOB
> > > > was removed, it's always ok to use kfree() and thus also kfree_rcu() on
> > > > allocations from kmem_cache_alloc() in addition to kmalloc(). Thus, such
> > > > call_rcu() users might be simplified to kfree_rcu(). I found some cases
> > > > semi-manually, but I'd expect coccinelle could help here so if anyone
> > > > wants
> > > > to take this task, feel free to.
> > >
> > > Thanks for the suggestion! I will try to look into it.
> >
> > Thank you both!
>
> I found the following functions. Do you want some other information, such
> as where they are called from?
Thank you!
> Ignore the -s at the beginning of some lines. Those are for emphasis. not
> to suggest to remove the code.
Well, the idea is to remove not only those lines, but the functions
containing them as well. ;-)
Then each call_rcu() function becomes kfree_rcu().
> I checked that the functions are only used in calls to call_rcu.
Good point, I had forgotten about that possibility!
> Without more effort, Coccinelle only looks for functions defined in the
> same file. Here are the functions that are passed to call_rcu where the
> function is not defined in the same file:
>
> need definition for audit_free_rule_rcu
> need definition for __i915_gem_free_object_rcu
> need definition for io_eventfd_ops
> need definition for ip_vs_dest_dst_rcu_free
> need definition for __put_task_struct_rcu_cb
> need definition for radix_tree_node_rcu_free
>
> They all do something more, although radix_tree_node_rcu_free doesn't do
> much more (some memsets).
Those might be important in order to handle the possibility of readers
holding a reference to a given block of memory across the time that it
is freed and then reallocated, but I cannot say for sure.
In most cases, the reinitialization at reallocation time suffices.
Thanx, Paul
> julia
>
> diff -u -p /home/jll/linux/drivers/net/wireguard/allowedips.c
> /tmp/nothing/drivers/net/wireguard/allowedips.c
> --- /home/jll/linux/drivers/net/wireguard/allowedips.c
> +++ /tmp/nothing/drivers/net/wireguard/allowedips.c
> @@ -50,7 +50,6 @@ static void push_rcu(struct allowedips_n
>
> static void node_free_rcu(struct rcu_head *rcu)
> {
> - kmem_cache_free(node_cache, container_of(rcu, struct allowedips_node,
> rcu));
> }
>
> static void root_free_rcu(struct rcu_head *rcu)
> diff -u -p /home/jll/linux/fs/ecryptfs/dentry.c
> /tmp/nothing/fs/ecryptfs/dentry.c
> --- /home/jll/linux/fs/ecryptfs/dentry.c
> +++ /tmp/nothing/fs/ecryptfs/dentry.c
> @@ -53,8 +53,6 @@ struct kmem_cache *ecryptfs_dentry_info_
>
> static void ecryptfs_dentry_free_rcu(struct rcu_head *head)
> {
> - kmem_cache_free(ecryptfs_dentry_info_cache,
> - container_of(head, struct ecryptfs_dentry_info, rcu));
> }
>
> /**
> diff -u -p /home/jll/linux/kernel/fork.c /tmp/nothing/kernel/fork.c
> --- /home/jll/linux/kernel/fork.c
> +++ /tmp/nothing/kernel/fork.c
> @@ -378,7 +378,6 @@ static struct kmem_cache *thread_stack_c
>
> static void thread_stack_free_rcu(struct rcu_head *rh)
> {
> - kmem_cache_free(thread_stack_cache, rh);
> }
>
> static void thread_stack_delayed_free(struct task_struct *tsk)
> diff -u -p /home/jll/linux/kernel/workqueue.c /tmp/nothing/kernel/workqueue.c
> --- /home/jll/linux/kernel/workqueue.c
> +++ /tmp/nothing/kernel/workqueue.c
> @@ -5024,8 +5024,6 @@ fail:
>
> static void rcu_free_pwq(struct rcu_head *rcu)
> {
> - kmem_cache_free(pwq_cache,
> - container_of(rcu, struct pool_workqueue, rcu));
> }
>
> /*
> diff -u -p /home/jll/linux/net/ipv4/inetpeer.c
> /tmp/nothing/net/ipv4/inetpeer.c
> --- /home/jll/linux/net/ipv4/inetpeer.c
> +++ /tmp/nothing/net/ipv4/inetpeer.c
> @@ -130,7 +130,6 @@ static struct inet_peer *lookup(const st
>
> static void inetpeer_free_rcu(struct rcu_head *head)
> {
> - kmem_cache_free(peer_cachep, container_of(head, struct inet_peer, rcu));
> }
>
> /* perform garbage collect on all items stacked during a lookup */
> diff -u -p /home/jll/linux/net/ipv6/xfrm6_tunnel.c
> /tmp/nothing/net/ipv6/xfrm6_tunnel.c
> --- /home/jll/linux/net/ipv6/xfrm6_tunnel.c
> +++ /tmp/nothing/net/ipv6/xfrm6_tunnel.c
> @@ -180,8 +180,6 @@ EXPORT_SYMBOL(xfrm6_tunnel_alloc_spi);
>
> static void x6spi_destroy_rcu(struct rcu_head *head)
> {
> - kmem_cache_free(xfrm6_tunnel_spi_kmem,
> - container_of(head, struct xfrm6_tunnel_spi, rcu_head));
> }
>
> static void xfrm6_tunnel_free_spi(struct net *net, xfrm_address_t *saddr)
> diff -u -p /home/jll/linux/security/security.c
> /tmp/nothing/security/security.c
> --- /home/jll/linux/security/security.c
> +++ /tmp/nothing/security/security.c
> @@ -1599,7 +1599,6 @@ static void inode_free_by_rcu(struct rcu
> /*
> * The rcu head is at the start of the inode blob
> */
> - kmem_cache_free(lsm_inode_cache, head);
> }
>
> /**
