linux-kernel - Re: [PATCH] drivers/dma/dma-jz4780: Fix race condition between probe and irq handler

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Message-ID: <20200821031616.GA7874@madhuparna-HP-Notebook>
Date:   Fri, 21 Aug 2020 08:46:16 +0530
From:   Madhuparna Bhowmik <madhuparnabhowmik10@...il.com>
To:     Paul Cercueil <paul@...pouillou.net>
Cc:     Lars-Peter Clausen <lars@...afoo.de>,
        madhuparnabhowmik10@...il.com, dan.j.williams@...el.com,
        vkoul@...nel.org, dmaengine@...r.kernel.org,
        linux-kernel@...r.kernel.org, andrianov@...ras.ru,
        ldv-project@...uxtesting.org
Subject: Re: [PATCH] drivers/dma/dma-jz4780: Fix race condition between probe
 and irq handler

On Thu, Aug 20, 2020 at 08:46:43PM +0200, Paul Cercueil wrote:
> 
> 
> Le jeu. 20 août 2020 à 20:23, Lars-Peter Clausen <lars@...afoo.de> a écrit :
> > On 8/20/20 1:59 PM, Paul Cercueil wrote:
> > > Hi,
> > > 
> > > Le dim. 16 août 2020 à 12:52, madhuparnabhowmik10@...il.com a écrit
> > > :
> > > > From: Madhuparna Bhowmik <madhuparnabhowmik10@...il.com>
> > > > 
> > > > In probe IRQ is requested before zchan->id is initialized which
> > > > can be
> > > > read in the irq handler. Hence, shift request irq and enable
> > > > clock after
> > > > other initializations complete. Here, enable clock part is not
> > > > part of
> > > > the race, it is just shifted down after request_irq to keep the
> > > > error
> > > > path same as before.
> > > > 
> > > > Found by Linux Driver Verification project (linuxtesting.org).
> > > > 
> > > > Signed-off-by: Madhuparna Bhowmik <madhuparnabhowmik10@...il.com>
> > > 
> > > I don't think there is a race at all, the interrupt handler won't be
> > > called before the DMA is registered.
> > > 
> > From a purely formal verification perspective there is a bug. The
> > interrupt could fire if i.e. the hardware is buggy or something. In
> > general it is a good idea to not request the IRQ until all the resources
> > that are used in the interrupt handler are properly set up. Even if you
> > know that in practice the interrupt will never fire this early.
> > 
>
> Fair enough, I'm fine with that, but the patch should be reworked so that
> the clk_prepare_enable() call is not moved.
>

Sure, I will send the v2 of the patch with this change soon.

Thanks,
Madhuparna
> Cheers,
> -Paul
> 
>