linux-kernel - Re: [PATCH tip/core/rcu 3/6] rcu: Abstract dynticks extended quiescent state enter/exit operations

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: <20170116164337.GB6500@twins.programming.kicks-ass.net>
Date:   Mon, 16 Jan 2017 17:43:37 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
Cc:     linux-kernel@...r.kernel.org, mingo@...nel.org,
        jiangshanlai@...il.com, dipankar@...ibm.com,
        akpm@...ux-foundation.org, mathieu.desnoyers@...icios.com,
        josh@...htriplett.org, tglx@...utronix.de, rostedt@...dmis.org,
        dhowells@...hat.com, edumazet@...gle.com, dvhart@...ux.intel.com,
        fweisbec@...il.com, oleg@...hat.com, bobby.prani@...il.com
Subject: Re: [PATCH tip/core/rcu 3/6] rcu: Abstract dynticks extended
 quiescent state enter/exit operations

On Sat, Jan 14, 2017 at 12:54:42AM -0800, Paul E. McKenney wrote:
>  /*
> + * Record entry into an extended quiescent state.  This is only to be
> + * called when not already in an extended quiescent state.
> + */
> +static void rcu_dynticks_eqs_enter(void)
> +{
> +	struct rcu_dynticks *rdtp = this_cpu_ptr(&rcu_dynticks);
> +
> +	/*
> +	 * CPUs seeing atomic_inc() must see prior RCU read-side critical
> +	 * sections, and we also must force ordering with the next idle
> +	 * sojourn.
> +	 */
> +	smp_mb__before_atomic(); /* See above. */
> +	atomic_inc(&rdtp->dynticks);
> +	smp_mb__after_atomic(); /* See above. */
> +	WARN_ON_ONCE(IS_ENABLED(CONFIG_RCU_EQS_DEBUG) &&
> +		     atomic_read(&rdtp->dynticks) & 0x1);
> +}

In an earlier patch you replaced things with atomic_add_return(), why
not use atomic_inc_return() here?