linux-kernel - Re: [RFC PATCH] rcu: using ACCESS_ONCE() to observe the jiffies

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <20100928232831.GC2419@linux.vnet.ibm.com>
Date:	Tue, 28 Sep 2010 16:28:31 -0700
From:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:	Dongdong Deng <dongdong.deng@...driver.com>
Cc:	dipankar@...ibm.com, linux-kernel@...r.kernel.org
Subject: Re: [RFC PATCH] rcu: using ACCESS_ONCE() to observe the
 jiffies_stall/rnp->qsmask value

On Tue, Sep 28, 2010 at 04:32:43PM +0800, Dongdong Deng wrote:
> Using ACCESS_ONCE() to observe the jiffies_stall/rnp->qsmask value
> due to the caller didn't hold the root_rcu/rnp node's lock.

Given that the quantities are only used once, ACCESS_ONCE() is strictly
speaking not necessary.  I am tempted to queue your patch regardless
for the documentation benefits.

Or is this patch necessary to fix a failure that you have been seeing?

In any case, thank you for taking a look at RCU!

							Thanx, Paul

> Signed-off-by: Dongdong Deng <dongdong.deng@...driver.com>
> CC: Dipankar Sarma <dipankar@...ibm.com>
> CC: Paul E. McKenney <paulmck@...ux.vnet.ibm.com>
> ---
>  kernel/rcutree.c |    4 ++--
>  1 files changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/kernel/rcutree.c b/kernel/rcutree.c
> index d5bc439..07a7063 100644
> --- a/kernel/rcutree.c
> +++ b/kernel/rcutree.c
> @@ -532,9 +532,9 @@ static void check_cpu_stall(struct rcu_state *rsp, struct rcu_data *rdp)
> 
>  	if (rcu_cpu_stall_panicking)
>  		return;
> -	delta = jiffies - rsp->jiffies_stall;
> +	delta = jiffies - ACCESS_ONCE(rsp->jiffies_stall);
>  	rnp = rdp->mynode;
> -	if ((rnp->qsmask & rdp->grpmask) && delta >= 0) {
> +	if ((ACCESS_ONCE(rnp->qsmask) & rdp->grpmask) && delta >= 0) {
> 
>  		/* We haven't checked in, so go dump stack. */
>  		print_cpu_stall(rsp);
> -- 
> 1.6.0.4
> 
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/