Re: [OMAP][sDMA]Fix for possible race condition in omap_free_dma()

[Artem Bityutskiy <dedekind@yandex.ru>]

Hi Tony,

I wonder, what happened to this patch?

Shilimkar, Santosh wrote:
> From: Santosh Shilimkar <santosh.shilimkar@ti.com>
> 
> Fix the possible race condition in omap_free_dma(). Function omap_free_dma() 
> sets the dev_id = -1 and then accesses the channel afterwards to clear it.
> But setting the dev_id=-1 makes the channel available for allocation again.
> So it is possible someone else can grab it and results are unpredictable.
> To avod this DMA channle is cleared first and then the dev_id = -1 is set.
> 
> Thanks to McNeil, Sean <sean.mcneil@ti.com> for ointing out this issue.
> 
> Signed-off-by: Santosh Shilimkar <santosh.shilimkar@ti.com>
> ---
>  arch/arm/plat-omap/dma.c |   13 ++++++-------
>  1 files changed, 6 insertions(+), 7 deletions(-)
> 
> Index: omapkernel/arch/arm/plat-omap/dma.c
> ===================================================================
> --- omapkernel.orig/arch/arm/plat-omap/dma.c
> +++ omapkernel/arch/arm/plat-omap/dma.c
> @@ -785,19 +785,12 @@ void omap_free_dma(int lch)
>  {
>  	unsigned long flags;
>  
> -	spin_lock_irqsave(&dma_chan_lock, flags);
>  	if (dma_chan[lch].dev_id == -1) {
>  		pr_err("omap_dma: trying to free unallocated DMA channel %d\n",
>  		       lch);
> -		spin_unlock_irqrestore(&dma_chan_lock, flags);
>  		return;
>  	}
>  
> -	dma_chan[lch].dev_id = -1;
> -	dma_chan[lch].next_lch = -1;
> -	dma_chan[lch].callback = NULL;
> -	spin_unlock_irqrestore(&dma_chan_lock, flags);
> -
>  	if (cpu_class_is_omap1()) {
>  		/* Disable all DMA interrupts for the channel. */
>  		dma_write(0, CICR(lch));
> @@ -823,6 +816,12 @@ void omap_free_dma(int lch)
>  		dma_write(0, CCR(lch));
>  		omap_clear_dma(lch);
>  	}
> +
> +	spin_lock_irqsave(&dma_chan_lock, flags);
> +	dma_chan[lch].dev_id = -1;
> +	dma_chan[lch].next_lch = -1;
> +	dma_chan[lch].callback = NULL;
> +	spin_unlock_irqrestore(&dma_chan_lock, flags);
>  }
>  EXPORT_SYMBOL(omap_free_dma);
>  
> 
> Regards,
> Santosh
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-- 
Best Regards,
Artem Bityutskiy (Артём Битюцкий)
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