Re: [PATCH 09/12] misc: pci_endpoint_test: Do not write status in IRQ handler

[Manivannan Sadhasivam <mani@kernel.org>]

On Wed, Feb 15, 2023 at 12:21:52PM +0900, Damien Le Moal wrote:
> pci_endpoint_test_irqhandler() always rewrites the status register when
> an IRQ is raised, either as-is if STATUS_IRQ_RAISED is not set, or with
> STATUS_IRQ_RAISED cleared if that flag is set. The first case creates a
> race window with the endpoint side, meaning that the host side test
> driver may end up reading what it just wrote, thus loosing the real
> status as set by the endpoint side before raising the next interrupt.
> This can prevent detecting that the STATUS_IRQ_RAISED flag was set by
> the endpoint.
> 
> Remove this race window by not clearing the STATUS_IRQ_RAISED status
> flag and not rewriting that register for every IRQ received.
> 
> Signed-off-by: Damien Le Moal <damien.lemoal@opensource.wdc.com>

Reviewed-by: Manivannan Sadhasivam <mani@kernel.org>

Thanks,
Mani

> ---
>  drivers/misc/pci_endpoint_test.c | 3 ---
>  1 file changed, 3 deletions(-)
> 
> diff --git a/drivers/misc/pci_endpoint_test.c b/drivers/misc/pci_endpoint_test.c
> index e27d471cc847..c1370950c79d 100644
> --- a/drivers/misc/pci_endpoint_test.c
> +++ b/drivers/misc/pci_endpoint_test.c
> @@ -158,10 +158,7 @@ static irqreturn_t pci_endpoint_test_irqhandler(int irq, void *dev_id)
>  	if (reg & STATUS_IRQ_RAISED) {
>  		test->last_irq = irq;
>  		complete(&test->irq_raised);
> -		reg &= ~STATUS_IRQ_RAISED;
>  	}
> -	pci_endpoint_test_writel(test, PCI_ENDPOINT_TEST_STATUS,
> -				 reg);
>  
>  	return IRQ_HANDLED;
>  }
> -- 
> 2.39.1
> 

-- 
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