linux-kernel - Re: [PATCH v4 07/15] lockdep: Implement crossrelease feature

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Message-ID: <20170116151319.GE3144@twins.programming.kicks-ass.net>
Date:   Mon, 16 Jan 2017 16:13:19 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     Byungchul Park <byungchul.park@....com>
Cc:     mingo@...nel.org, tglx@...utronix.de, walken@...gle.com,
        boqun.feng@...il.com, kirill@...temov.name,
        linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        iamjoonsoo.kim@....com, akpm@...ux-foundation.org,
        npiggin@...il.com
Subject: Re: [PATCH v4 07/15] lockdep: Implement crossrelease feature

On Fri, Dec 09, 2016 at 02:12:03PM +0900, Byungchul Park wrote:
> +	/*
> +	 * We assign class_idx here redundantly even though following
> +	 * memcpy will cover it, in order to ensure a rcu reader can
> +	 * access the class_idx atomically without lock.
> +	 *
> +	 * Here we assume setting a word-sized variable is atomic.

which one, where?

> +	 */
> +	xlock->hlock.class_idx = hlock->class_idx;
> +	gen_id = (unsigned int)atomic_inc_return(&cross_gen_id);
> +	WRITE_ONCE(xlock->gen_id, gen_id);
> +	memcpy(&xlock->hlock, hlock, sizeof(struct held_lock));
> +	INIT_LIST_HEAD(&xlock->xlock_entry);
> +	list_add_tail_rcu(&xlock->xlock_entry, &xlocks_head);