linux-kernel - Re: [PATCH v2 1/2] dmaengine: pl330: fix descriptor allocation fail

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Message-ID: <20171020061720.GN30097@localhost>
Date:   Fri, 20 Oct 2017 11:47:20 +0530
From:   Vinod Koul <vinod.koul@...el.com>
To:     Alexander Kochetkov <al.kochet@...il.com>
Cc:     dmaengine@...r.kernel.org, linux-kernel@...r.kernel.org,
        Dan Williams <dan.j.williams@...el.com>,
        Marek Szyprowski <m.szyprowski@...sung.com>,
        Krzysztof Kozlowski <krzk@...nel.org>
Subject: Re: [PATCH v2 1/2] dmaengine: pl330: fix descriptor allocation fail

On Wed, Oct 04, 2017 at 02:37:23PM +0300, Alexander Kochetkov wrote:
> If two concurrent threads call pl330_get_desc() when DMAC descriptor
> pool is empty it is possible that allocation for one of threads will fail
> with message:
> 
> kernel: dma-pl330 20078000.dma-controller: pl330_get_desc:2469 ALERT!
> 
> Here how that can happen. Thread A calls pl330_get_desc() to get
> descriptor. If DMAC descriptor pool is empty pl330_get_desc() allocates
> new descriptor on shared pool using add_desc() and then get newly
> allocated descriptor using pluck_desc(). At the same time thread B calls
> pluck_desc() and take newly allocated descriptor. In that case descriptor
> allocation for thread A will fail.
> 
> Using on-stack pool for new descriptor allow avoid the issue described.
> The patch modify pl330_get_desc() to use on-stack pool for allocation
> new descriptors.

Applied, thanks

-- 
~Vinod