linux-kernel - Re: [PATCH 01/16] crypto: caam - Remove unnecessary smp_read_barrier

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Message-ID: <20141113201001.GQ4460@linux.vnet.ibm.com>
Date:	Thu, 13 Nov 2014 12:10:01 -0800
From:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:	Pranith Kumar <bobby.prani@...il.com>
Cc:	Herbert Xu <herbert@...dor.apana.org.au>,
	"David S. Miller" <davem@...emloft.net>,
	Horia Geanta <horia.geanta@...escale.com>,
	Michael Neuling <mikey@...ling.org>,
	Kim Phillips <kim.phillips@...escale.com>,
	Wolfram Sang <wsa@...-dreams.de>,
	Cristian Stoica <cristian.stoica@...escale.com>,
	"open list:CRYPTO API" <linux-crypto@...r.kernel.org>,
	open list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 01/16] crypto: caam - Remove unnecessary
 smp_read_barrier_depends()

On Thu, Nov 13, 2014 at 02:24:07PM -0500, Pranith Kumar wrote:
> Recently lockless_dereference() was added which can be used in place of
> hard-coding smp_read_barrier_depends(). The following PATCH makes the change.
> 
> Signed-off-by: Pranith Kumar <bobby.prani@...il.com>
> ---
>  drivers/crypto/caam/jr.c | 3 ---
>  1 file changed, 3 deletions(-)
> 
> diff --git a/drivers/crypto/caam/jr.c b/drivers/crypto/caam/jr.c
> index bae20d8..9b3ef1bc 100644
> --- a/drivers/crypto/caam/jr.c
> +++ b/drivers/crypto/caam/jr.c
> @@ -181,8 +181,6 @@ static void caam_jr_dequeue(unsigned long devarg)
>  		for (i = 0; CIRC_CNT(head, tail + i, JOBR_DEPTH) >= 1; i++) {
>  			sw_idx = (tail + i) & (JOBR_DEPTH - 1);
> 
> -			smp_read_barrier_depends();
> -

Did you mean to add a lockless_dereference() somewhere?  I would guess
that one is required on the load into sw_idx before the "for" loop,
but I cannot claim to be familiar with this code.

							Thanx, Paul

>  			if (jrp->outring[hw_idx].desc ==
>  			    jrp->entinfo[sw_idx].desc_addr_dma)
>  				break; /* found */
> @@ -218,7 +216,6 @@ static void caam_jr_dequeue(unsigned long devarg)
>  		if (sw_idx == tail) {
>  			do {
>  				tail = (tail + 1) & (JOBR_DEPTH - 1);
> -				smp_read_barrier_depends();
>  			} while (CIRC_CNT(head, tail, JOBR_DEPTH) >= 1 &&
>  				 jrp->entinfo[tail].desc_addr_dma == 0);
> 
> -- 
> 1.9.1
> 

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