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

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Date:   Sat, 23 Apr 2022 20:15:02 +0530
From:   Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>
To:     Serge Semin <fancer.lancer@...il.com>
Cc:     Serge Semin <Sergey.Semin@...kalelectronics.ru>,
        Gustavo Pimentel <gustavo.pimentel@...opsys.com>,
        Vinod Koul <vkoul@...nel.org>,
        Jingoo Han <jingoohan1@...il.com>,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        Frank Li <Frank.Li@....com>,
        Alexey Malahov <Alexey.Malahov@...kalelectronics.ru>,
        Pavel Parkhomenko <Pavel.Parkhomenko@...kalelectronics.ru>,
        Lorenzo Pieralisi <lorenzo.pieralisi@....com>,
        Rob Herring <robh@...nel.org>,
        Krzysztof Wilczyński <kw@...ux.com>,
        linux-pci@...r.kernel.org, dmaengine@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 24/25] dmaengine: dw-edma: Skip cleanup procedure if no
 private data found

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@...kalelectronics.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
> > >