Re: [PATCH v4 9/9] dmaengine: dw-edma: Defer channel IRQ handling to workqueue

[sashiko-bot@kernel.org]

Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:

Pre-existing issues:
- [High] Interrupts are requested before critical channel structures are fully initialized, leading to possible NULL pointer dereferences or uninitialized lock acquisitions on early or shared interrupts.
--

--- Patch [9]: [PATCH v4 9/9] dmaengine: dw-edma: Defer channel IRQ handling to workqueue ---
commit 9d2ebede7ce8b472f3d4f1a246b418b61a57de7a
Author: Koichiro Den <den@valinux.co.jp>

dmaengine: dw-edma: Defer channel IRQ handling to workqueue

This commit shifts channel IRQ handling from hard IRQ context to workqueues.
It keeps the hard IRQ handler minimal to clear status and dispatch channel
events, while deferring per-channel processing to work items to improve
concurrency.

> diff --git a/drivers/dma/dw-edma/dw-edma-core.c b/drivers/dma/dw-edma/dw-edma-core.c
> --- a/drivers/dma/dw-edma/dw-edma-core.c
> +++ b/drivers/dma/dw-edma/dw-edma-core.c
[ ... ]
> @@ -1190,10 +1232,21 @@ int dw_edma_probe(struct dw_edma_chip *chip)
>  	/* Disable eDMA, only to establish the ideal initial conditions */
>  	dw_edma_core_off(dw);
>  
> +	/*
> +	 * Deferred IRQ works are queued from the hard IRQ handlers, so the
> +	 * workqueue must exist before any IRQ is requested.
> +	 */
> +	dw->wq = alloc_workqueue("dw-edma:%s", WQ_UNBOUND | WQ_HIGHPRI, 0,
> +				 dev_name(chip->dev));
> +	if (!dw->wq)
> +		return -ENOMEM;
> +
>  	/* Request IRQs */
>  	err = dw_edma_irq_request(dw, &wr_alloc, &rd_alloc);

[Severity: High]
This is a pre-existing issue, but requesting interrupts here before critical
channel structures are initialized can lead to a NULL pointer dereference.

Since dw_edma_irq_request() uses IRQF_SHARED, an interrupt from another
device sharing the line could fire immediately.

If that happens before dw_edma_channel_setup() completes, the handler
(like dw_edma_interrupt_emulated()) will unconditionally dereference the
uninitialized dw_irq->dw pointer.

Additionally, the deferred work items might attempt to acquire chan->vc.lock
before vchan_init() has been called in dw_edma_channel_setup().

Does the initialization order need to be adjusted so that structures are fully
setup before interrupts are requested?

> -	if (err)
> +	if (err) {
> +		destroy_workqueue(dw->wq);
>  		return err;
> +	}
>  
>  	/* Allocate a dedicated virtual IRQ for interrupt-emulation doorbells */
>  	err = dw_edma_emul_irq_alloc(dw);

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/20260716152503.1747922-1-den@valinux.co.jp?part=9