linux-kernel - Re: [PATCH v7 6/8] fsl-dma: use spin_lock_bh to instead of spin_lock

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Date:	Sun, 2 Sep 2012 01:41:18 -0700
From:	Dan Williams <djbw@...com>
To:	qiang.liu@...escale.com
Cc:	linux-crypto@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org,
	linux-kernel@...r.kernel.org, vinod.koul@...el.com,
	kim.phillips@...escale.com, herbert@...dor.hengli.com.au,
	davem@...emloft.net, arnd@...db.de, gregkh@...uxfoundation.org,
	Li Yang <leoli@...escale.com>, Timur Tabi <timur@...escale.com>
Subject: Re: [PATCH v7 6/8] fsl-dma: use spin_lock_bh to instead of spin_lock_irqsave

On Thu, Aug 9, 2012 at 1:23 AM,  <qiang.liu@...escale.com> wrote:
> From: Qiang Liu <qiang.liu@...escale.com>
>
> The use of spin_lock_irqsave() is a stronger locking mechanism than is
> required throughout the driver. The minimum locking required should be
> used instead. Interrupts will be turned off and context will be saved,
> there is needless to use irqsave.
>
> Change all instances of spin_lock_irqsave() to spin_lock_bh().
> All manipulation of protected fields is done using tasklet context or
> weaker, which makes spin_lock_bh() the correct choice.

It seems you are coordinating fsl-dma copy and talitos xor operations.
 It looks like fsl-dma will be called through
talitos_process_pending()->dma_run_dependencies(), which is
potentially called in hard irq context.

This all comes back to the need to fix raid offload to manage the
channels explicitly rather than the current dependency chains.

--
Dan
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