linux-kernel - Re: [PATCH 07/12] rwsem: wake queued readers when writer blocks on active read lock

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Message-ID: <25280.1273667611@redhat.com>
Date:	Wed, 12 May 2010 13:33:31 +0100
From:	David Howells <dhowells@...hat.com>
To:	Michel Lespinasse <walken@...gle.com>
Cc:	dhowells@...hat.com,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Ingo Molnar <mingo@...e.hu>,
	Thomas Gleixner <tglx@...utronix.de>,
	LKML <linux-kernel@...r.kernel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Mike Waychison <mikew@...gle.com>,
	Suleiman Souhlal <suleiman@...gle.com>,
	Ying Han <yinghan@...gle.com>
Subject: Re: [PATCH 07/12] rwsem: wake queued readers when writer blocks on active read lock

Michel Lespinasse <walken@...gle.com> wrote:

> +	/* if there are no active locks, wake the front queued process(es) up.
> +	 *
> +	 * or if we're called from a failed down_write(), and there were
> +	 * already threads queued before us, and there are no active writers,
> +	 * the lock must be read owned; try to wake any read locks that were
> +	 * queued ahead of us. */

That looks weird.  Can I suggest rewriting it thus:

	/* If there are no active locks, wake the front queued process(es) up.
	 *
	 * Alternatively, if we're called from a failed down_write(), there
	 * were already threads queued before us and there are no active
	 * writers, the lock must be read owned; so we try to wake any read
	 * locks that were queued ahead of us. */

David
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