linux-kernel - Re: [RFC] block: change to use atomic_inc_return

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Message-ID: <564AA13C.108@kernel.dk>
Date:	Mon, 16 Nov 2015 20:38:36 -0700
From:	Jens Axboe <axboe@...nel.dk>
To:	yalin wang <yalin.wang2010@...il.com>, linux-kernel@...r.kernel.org
Subject: Re: [RFC] block: change to use atomic_inc_return_release()

On 11/16/2015 08:24 PM, yalin wang wrote:
> Some arch define this atomic_inc_return_release() OP.

That is a very vague commit message, you'll need a whole lot more than 
that... A commit message is supposed to describe the reason for the 
change. You provide no reason for the change.

> diff --git a/block/bio.c b/block/bio.c
> index fbc558b..b251857 100644
> --- a/block/bio.c
> +++ b/block/bio.c
> @@ -310,8 +310,7 @@ static void bio_chain_endio(struct bio *bio, int error)
>   static inline void bio_inc_remaining(struct bio *bio)
>   {
>   	bio->bi_flags |= (1 << BIO_CHAIN);
> -	smp_mb__before_atomic();
> -	atomic_inc(&bio->__bi_remaining);
> +	atomic_inc_return_release(&bio->__bi_remaining);

Are these equivalent? Where's the documentation for this primitive? The 
previous code ensured that we ordered the dec of the remaining count 
with the update of the flags.

-- 
Jens Axboe

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