linux-kernel - Re: [PATCH 2/5] dmaengine: Call module_put() after device_free_chan

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Message-ID: <20191224043713.GH2536@vkoul-mobl>
Date:   Tue, 24 Dec 2019 10:07:13 +0530
From:   Vinod Koul <vkoul@...nel.org>
To:     Logan Gunthorpe <logang@...tatee.com>
Cc:     linux-kernel@...r.kernel.org, dmaengine@...r.kernel.org,
        Dan Williams <dan.j.williams@...el.com>,
        Dave Jiang <dave.jiang@...el.com>, Kit Chow <kchow@...aio.com>
Subject: Re: [PATCH 2/5] dmaengine: Call module_put() after
 device_free_chan_resources()

On 16-12-19, 12:01, Logan Gunthorpe wrote:
> The module reference is taken to ensure the callbacks still exist
> when they are called. If the channel holds the last reference to the
> module, the module can disappear before device_free_chan_resources() is
> called and would cause a call into free'd memory.
> 
> Signed-off-by: Logan Gunthorpe <logang@...tatee.com>
> ---
>  drivers/dma/dmaengine.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/dma/dmaengine.c b/drivers/dma/dmaengine.c
> index 4b604086b1b3..776fdf535a3a 100644
> --- a/drivers/dma/dmaengine.c
> +++ b/drivers/dma/dmaengine.c
> @@ -250,7 +250,6 @@ static void dma_chan_put(struct dma_chan *chan)
>  		return;
>  
>  	chan->client_count--;
> -	module_put(dma_chan_to_owner(chan));
>  
>  	/* This channel is not in use anymore, free it */
>  	if (!chan->client_count && chan->device->device_free_chan_resources) {
> @@ -259,6 +258,8 @@ static void dma_chan_put(struct dma_chan *chan)
>  		chan->device->device_free_chan_resources(chan);
>  	}
>  
> +	module_put(dma_chan_to_owner(chan));
> +
>  	/* If the channel is used via a DMA request router, free the mapping */
>  	if (chan->router && chan->router->route_free) {
>  		chan->router->route_free(chan->router->dev, chan->route_data);

I think this should be moved here after route_free() and will take care
of route cleanup as well

Thanks
-- 
~Vinod