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

[Paul Cercueil]

Le jeu. 20 août 2020 à 20:23, Lars-Peter Clausen <lars@xxxxxxxxxx> a 
écrit :
> On 8/20/20 1:59 PM, Paul Cercueil wrote:
> > Hi,
> >
> > Le dim. 16 août 2020 à 12:52, madhuparnabhowmik10@xxxxxxxxx a 
> > écrit :
> > > From: Madhuparna Bhowmik <madhuparnabhowmik10@xxxxxxxxx>
> > >
> > > 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@xxxxxxxxx>
> >
> > 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.

Cheers,
-Paul