Re: [PATCH 24/25] dmaengine: dw-edma: Skip cleanup procedure if no private data found

From: Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>
To: Serge Semin <fancer.lancer@gmail.com>
Cc: "Serge Semin" <Sergey.Semin@baikalelectronics.ru>,
	"Gustavo Pimentel" <gustavo.pimentel@synopsys.com>,
	"Vinod Koul" <vkoul@kernel.org>,
	"Jingoo Han" <jingoohan1@gmail.com>,
	"Bjorn Helgaas" <bhelgaas@google.com>,
	"Frank Li" <Frank.Li@nxp.com>,
	"Alexey Malahov" <Alexey.Malahov@baikalelectronics.ru>,
	"Pavel Parkhomenko" <Pavel.Parkhomenko@baikalelectronics.ru>,
	"Lorenzo Pieralisi" <lorenzo.pieralisi@arm.com>,
	"Rob Herring" <robh@kernel.org>,
	"Krzysztof Wilczyński" <kw@linux.com>,
	linux-pci@vger.kernel.org, dmaengine@vger.kernel.org,
	linux-kernel@vger.kernel.org
Subject: Re: [PATCH 24/25] dmaengine: dw-edma: Skip cleanup procedure if no private data found
Date: Sat, 23 Apr 2022 20:15:02 +0530	[thread overview]
Message-ID: <20220423144502.GS374560@thinkpad> (raw)
In-Reply-To: <20220418134833.awogzzfq745mc5dm@mobilestation>

On Mon, Apr 18, 2022 at 04:48:33PM +0300, Serge Semin wrote:
> On Fri, Mar 25, 2022 at 11:45:03PM +0530, Manivannan Sadhasivam wrote:
> > On Thu, Mar 24, 2022 at 04:48:35AM +0300, Serge Semin wrote:
> > > DW eDMA driver private data is preserved in the passed DW eDMA chip info
> > > structure. If either probe procedure failed or for some reason the passed
> > > info object doesn't have private data pointer initialized we need to halt
> > > the DMA device cleanup procedure in order to prevent possible system
> > > crashes.
> > > 
> > 
> 
> > How come remove() could happen when probe() failed? If you hit this issue then
> > something else is utterly going wrong.
> 
> It fully depends on the DW eDMA client driver implementation, which
> can't and in general shouldn't be guessed. But what must be done in
> the DW eDMA driver is a protection against the invalid data being
> passed to the exported API methods. That wrong situation must be
> detected and handled in the API user code. It's much easier to do by
> having an error code returned from the dw_edma_remove() method than
> catching random system crashes.
> 

Even though I don't see any practical issue, I'm fine with this.

Thanks,
Mani

> -Sergey
> 
> > 
> > Thanks,
> > Mani
> > 
> > > Signed-off-by: Serge Semin <Sergey.Semin@baikalelectronics.ru>
> > > ---
> > >  drivers/dma/dw-edma/dw-edma-core.c | 4 ++++
> > >  1 file changed, 4 insertions(+)
> > > 
> > > diff --git a/drivers/dma/dw-edma/dw-edma-core.c b/drivers/dma/dw-edma/dw-edma-core.c
> > > index ca5cd7c99571..b932682a8ba8 100644
> > > --- a/drivers/dma/dw-edma/dw-edma-core.c
> > > +++ b/drivers/dma/dw-edma/dw-edma-core.c
> > > @@ -1030,6 +1030,10 @@ int dw_edma_remove(struct dw_edma_chip *chip)
> > >  	struct dw_edma *dw = chip->dw;
> > >  	int i;
> > >  
> > > +	/* Skip removal if no private data found */
> > > +	if (!dw)
> > > +		return -ENODEV;
> > > +
> > >  	/* Disable eDMA */
> > >  	dw_edma_v0_core_off(dw);
> > >  
> > > -- 
> > > 2.35.1
> > > 