linux-kernel - Re: [PATCH 2/2] dmaengine: qcom_hidma: fix handoff FIFO memory leak on driver removal

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Message-ID: <aE8bu2woUe96DVo-@gmail.com>
Date: Sun, 15 Jun 2025 20:15:07 +0100
From: Qasim Ijaz <qasdev00@...il.com>
To: Sinan Kaya <Okaya@...nel.org>
Cc: Eugen Hristev <eugen.hristev@...aro.org>, Vinod Koul <vkoul@...nel.org>,
	linux-arm-kernel@...ts.infradead.org, linux-arm-msm@...r.kernel.org,
	dmaengine@...r.kernel.org, linux-kernel@...r.kernel.org,
	stable@...r.kernel.org
Subject: Re: [PATCH 2/2] dmaengine: qcom_hidma: fix handoff FIFO memory leak
 on driver removal

On Fri, Jun 06, 2025 at 09:35:44AM -0400, Sinan Kaya wrote:
> 
> On 6/5/2025 9:04 AM, Eugen Hristev wrote:
> > > diff --git a/drivers/dma/qcom/hidma_ll.c b/drivers/dma/qcom/hidma_ll.c
> > > index fee448499777..0c2bae46746c 100644
> > > --- a/drivers/dma/qcom/hidma_ll.c
> > > +++ b/drivers/dma/qcom/hidma_ll.c
> > > @@ -816,6 +816,7 @@ int hidma_ll_uninit(struct hidma_lldev *lldev)
> > >   	required_bytes = sizeof(struct hidma_tre) * lldev->nr_tres;
> > >   	tasklet_kill(&lldev->task);
> > > +	kfifo_free(&lldev->handoff_fifo);
> > >   	memset(lldev->trepool, 0, required_bytes);
> > >   	lldev->trepool = NULL;
> > >   	atomic_set(&lldev->pending_tre_count, 0);
> > Is it possible that the handoff_fifo is freed, then we could observe
> > reset complete interrupts before they are being cleared in
> > hidma_ll_uninit later on, which would lead to the following call chain
> > 
> >   hidma_ll_inthandler - hidma_ll_int_handler_internal -
> > hidma_handle_tre_completion - hidma_post_completed -
> > tasklet_schedule(&lldev->task); - hidma_ll_tre_complete - kfifo_out
> 
> According to the documentation, the way to guarantee this from not happening
> 
> is to call tasklet_disable() to ensure that tasklet completes execution.
> Only after that
> 
> data structures used by the tasklet can be freed.
> 
> I think proper order is:
> 
> 1. tasklet_disable
> 
> 2. tasklet_kill
> 
> 3. kfifo_free

Hi Sinan, hi Eugen,

Thanks for reviewing the patch and for pointing out the correct
shutdown ordering.

If you’re both happy with it, I’ll send a v2 that calls
tasklet_disable() before tasklet_kill(), then frees the handoff_fifo.

Just let me know and I’ll resend.

Thanks
Qasim
> 
> 
>