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

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Message-ID: <20220418134833.awogzzfq745mc5dm@mobilestation>
Date:   Mon, 18 Apr 2022 16:48:33 +0300
From:   Serge Semin <fancer.lancer@...il.com>
To:     Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>
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 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.

-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
> >