linux-kernel - Re: [PATCH] dmaengine: imx-sdma: fix deadlock in interrupt handler

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Date:   Mon, 25 Sep 2023 11:27:08 +0200
From:   Sascha Hauer <s.hauer@...gutronix.de>
To:     Uwe Kleine-König 
        <u.kleine-koenig@...gutronix.de>
Cc:     Tim van der Staaij | Zign <Tim.vanderstaaij@...ngroup.com>,
        Fabio Estevam <festevam@...il.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Vinod Koul <vkoul@...nel.org>,
        Pengutronix Kernel Team <kernel@...gutronix.de>,
        "dmaengine@...r.kernel.org" <dmaengine@...r.kernel.org>,
        Shawn Guo <shawnguo@...nel.org>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH] dmaengine: imx-sdma: fix deadlock in interrupt handler

On Mon, Sep 25, 2023 at 11:20:04AM +0200, Uwe Kleine-König wrote:
> Hello,
> 
> On Thu, Sep 21, 2023 at 09:57:11AM +0000, Tim van der Staaij | Zign wrote:
> > dev_warn internally acquires the lock that is already held when
> > sdma_update_channel_loop is called. Therefore it is acquired twice and
> > this is detected as a deadlock. Temporarily release the lock while
> > logging to avoid this.
> > 
> > Signed-off-by: Tim van der Staaij <tim.vanderstaaij@...ngroup.com>
> > Link: https://lore.kernel.org/all/AM0PR08MB308979EC3A8A53AE6E2D3408802CA@AM0PR08MB3089.eurprd08.prod.outlook.com/
> > ---
> >  drivers/dma/imx-sdma.c | 3 +++
> >  1 file changed, 3 insertions(+)
> > 
> > diff --git a/drivers/dma/imx-sdma.c b/drivers/dma/imx-sdma.c
> > index 51012bd39900..3a7cd783a567 100644
> > --- a/drivers/dma/imx-sdma.c
> > +++ b/drivers/dma/imx-sdma.c
> > @@ -904,7 +904,10 @@ static void sdma_update_channel_loop(struct sdma_channel *sdmac)
> >  	 * owned buffer is available (i.e. BD_DONE was set too late).
> >  	 */
> >  	if (sdmac->desc && !is_sdma_channel_enabled(sdmac->sdma, sdmac->channel)) {
> > +		spin_unlock(&sdmac->vc.lock);
> >  		dev_warn(sdmac->sdma->dev, "restart cyclic channel %d\n", sdmac->channel);
> > +		spin_lock(&sdmac->vc.lock);
> > +
> 
> I don't know if Sascha's patch helps

I do ;)

I inserted a dev_info() into the imx-sdma driver and got said circular
locking warning. With my patch applied it's gone. Nevertheless I would
wait for Tims feedback and resend it with some more people on Cc. I
never used lockdep_set_subclass() and I am not sure if it's legal to
put it into the UART startup function like I did.

Sascha

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