Re: [PATCH] Keys: Improve usage of memory barriers and remove IRQ disablement

[Nick Piggin <nickpiggin@yahoo.com.au>]

David Howells wrote:

> diff --git a/security/keys/key.c b/security/keys/key.c
> index 99781b7..d8a6e00 100644
> --- a/security/keys/key.c
> +++ b/security/keys/key.c
> @@ -619,6 +619,7 @@ void key_put(struct key *key)
>  	if (key) {
>  		key_check(key);
>  
> +		smp_mb__before_atomic_dec();
>  		if (atomic_dec_and_test(&key->usage))
>  			schedule_work(&key_cleanup_task);

Shouldn't be needed: Documentation/atomic_ops.txt specifies that any atomic_
which both modifies its atomic operand and returns something is to be a full
barrier before and after the operation.

This misuse occurs a few times in core code, which makes it a bit confusing.

However, I think it is nice to add a comment if these implicit barriers are
used, if the purpose is not really obvious.

--
SUSE Labs, Novell Inc.
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