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Subject: Re: [PATCH v5 05/14] dmaengine: tegra-apb: Prevent race conditions of
 tasklet vs free list
To:     Jon Hunter <jonathanh@nvidia.com>,
        Laxman Dewangan <ldewangan@nvidia.com>,
        Vinod Koul <vkoul@kernel.org>,
        Dan Williams <dan.j.williams@intel.com>,
        Thierry Reding <thierry.reding@gmail.com>,
        =?UTF-8?B?TWljaGHFgiBNaXJvc8WCYXc=?= <mirq-linux@rere.qmqm.pl>
Cc:     dmaengine@vger.kernel.org, linux-tegra@vger.kernel.org,
        linux-kernel@vger.kernel.org
References: <20200123230325.3037-1-digetx@gmail.com>
 <20200123230325.3037-6-digetx@gmail.com>
 <cd1da99a-e52e-e202-257d-17466132d088@nvidia.com>
From:   Dmitry Osipenko <digetx@gmail.com>
Message-ID: <5f867023-d49a-aff5-8d7f-d682a3b32770@gmail.com>
Date:   Wed, 29 Jan 2020 17:39:07 +0300
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29.01.2020 14:01, Jon Hunter пишет:
> 
> On 23/01/2020 23:03, Dmitry Osipenko wrote:
>> The interrupt handler puts a half-completed DMA descriptor on a free list
>> and then schedules tasklet to process bottom half of the descriptor that
>> executes client's callback, this creates possibility to pick up the busy
>> descriptor from the free list. Thus let's disallow descriptor's re-use
>> until it is fully processed.
>>
>> Acked-by: Jon Hunter <jonathanh@nvidia.com>
>> Signed-off-by: Dmitry Osipenko <digetx@gmail.com>
>> ---
>>  drivers/dma/tegra20-apb-dma.c | 2 +-
>>  1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/drivers/dma/tegra20-apb-dma.c b/drivers/dma/tegra20-apb-dma.c
>> index 1b8a11804962..aafad50d075e 100644
>> --- a/drivers/dma/tegra20-apb-dma.c
>> +++ b/drivers/dma/tegra20-apb-dma.c
>> @@ -281,7 +281,7 @@ static struct tegra_dma_desc *tegra_dma_desc_get(
>>  
>>  	/* Do not allocate if desc are waiting for ack */
>>  	list_for_each_entry(dma_desc, &tdc->free_dma_desc, node) {
>> -		if (async_tx_test_ack(&dma_desc->txd)) {
>> +		if (async_tx_test_ack(&dma_desc->txd) && !dma_desc->cb_count) {
>>  			list_del(&dma_desc->node);
>>  			spin_unlock_irqrestore(&tdc->lock, flags);
>>  			dma_desc->txd.flags = 0;
>>
> 
> I think we should mark this for stable as well. I would make this the
> 2nd patch in the series as it is related to #1.

Okay!