linux-kernel - Re: [PATCH 25/26] aio: use xchg() instead of completion

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Date:	Wed, 19 Dec 2012 19:59:03 +0800
From:	Hillf Danton <dhillf@...il.com>
To:	Kent Overstreet <koverstreet@...gle.com>
Cc:	Zach Brown <zab@...hat.com>, LKML <linux-kernel@...r.kernel.org>,
	Hillf Danton <dhillf@...il.com>
Subject: Re: [PATCH 25/26] aio: use xchg() instead of completion_lock

>@@ -686,9 +685,10 @@ void aio_complete(struct kiocb *iocb, long res, long res2)
> 	 * ctx->ctx_lock to prevent other code from messing with the tail
> 	 * pointer since we might be called from irq context.
> 	 */

Well the comment is stale.

Hillf
>-	spin_lock_irqsave(&ctx->completion_lock, flags);
>+	local_irq_save(flags);
>+	while ((tail = xchg(&ctx->tail, UINT_MAX)) == UINT_MAX)
>+		cpu_relax();
--
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