[PATCH] nfs: delegation: Replace rcu_assign_pointer() with RCU_INIT_POINTER()

[PATCH] nfs: delegation: Replace rcu_assign_pointer() with RCU_INIT_POINTER()

[Andreea-Cristina Bernat]

The use of "rcu_assign_pointer()" is NULLing out the pointer.
According to RCU_INIT_POINTER()'s block comment:
"1.   This use of RCU_INIT_POINTER() is NULLing out the pointer"
it is better to use it instead of rcu_assign_pointer() because it has a
smaller overhead.

The following Coccinelle semantic patch was used:
@@
@@

- rcu_assign_pointer
+ RCU_INIT_POINTER
  (..., NULL)

Signed-off-by: Andreea-Cristina Bernat <bernat.ada@gmail.com>
---
 fs/nfs/delegation.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/fs/nfs/delegation.c b/fs/nfs/delegation.c
index 5d8ccec..349e63b 100644
--- a/fs/nfs/delegation.c
+++ b/fs/nfs/delegation.c
@@ -249,7 +249,7 @@ nfs_detach_delegation_locked(struct nfs_inode *nfsi,
 	list_del_rcu(&delegation->super_list);
 	delegation->inode = NULL;
 	nfsi->delegation_state = 0;
-	rcu_assign_pointer(nfsi->delegation, NULL);
+	RCU_INIT_POINTER(nfsi->delegation, NULL);
 	spin_unlock(&delegation->lock);
 	return delegation;
 }
-- 
1.9.1

Re: [PATCH] nfs: delegation: Replace rcu_assign_pointer() with RCU_INIT_POINTER()

[Trond Myklebust]

On Fri, Aug 22, 2014 at 10:07 AM, Andreea-Cristina Bernat
<bernat.ada@gmail.com> wrote:
> The use of "rcu_assign_pointer()" is NULLing out the pointer.
> According to RCU_INIT_POINTER()'s block comment:
> "1.   This use of RCU_INIT_POINTER() is NULLing out the pointer"
> it is better to use it instead of rcu_assign_pointer() because it has a
> smaller overhead.
>
> The following Coccinelle semantic patch was used:
> @@
> @@
>
> - rcu_assign_pointer
> + RCU_INIT_POINTER
>   (..., NULL)
>
> Signed-off-by: Andreea-Cristina Bernat <bernat.ada@gmail.com>
> ---
>  fs/nfs/delegation.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/fs/nfs/delegation.c b/fs/nfs/delegation.c
> index 5d8ccec..349e63b 100644
> --- a/fs/nfs/delegation.c
> +++ b/fs/nfs/delegation.c
> @@ -249,7 +249,7 @@ nfs_detach_delegation_locked(struct nfs_inode *nfsi,
>         list_del_rcu(&delegation->super_list);
>         delegation->inode = NULL;
>         nfsi->delegation_state = 0;
> -       rcu_assign_pointer(nfsi->delegation, NULL);
> +       RCU_INIT_POINTER(nfsi->delegation, NULL);
>         spin_unlock(&delegation->lock);
>         return delegation;
>  }
> --
> 1.9.1

Sorry, but NACK.

We do need the memory barriers here, as the nfs_inode is globally
visible, and other threads may be checking nfsi->delegation_state
and/or delegation->inode in order to conclude whether or not there is
still a delegation associated with this inode.

Cheers
  Trond
-- 
Trond Myklebust

Linux NFS client maintainer, PrimaryData

trond.myklebust@primarydata.com