2023-08-06 03:48:20

by Duoming Zhou

Subject: [PATCH] dmaengine: mediatek: Fix deadlock caused by synchronize_irq()

The synchronize_irq(c->irq) will not return until the IRQ handler
mtk_uart_apdma_irq_handler() is completed. If the synchronize_irq()
holds a spin_lock and waits the IRQ handler to complete, but the
IRQ handler also needs the same spin_lock. The deadlock will happen.
The process is shown below:

cpu0 cpu1
mtk_uart_apdma_device_pause() | mtk_uart_apdma_irq_handler()
spin_lock_irqsave() |
| spin_lock_irqsave()
//hold the lock to wait |
synchronize_irq() |

This patch reorders the synchronize_irq(c->irq) outside the spin_lock
in order to mitigate the bug.

Fixes: 9135408c3ace ("dmaengine: mediatek: Add MediaTek UART APDMA support")
Signed-off-by: Duoming Zhou <[email protected]>
---
drivers/dma/mediatek/mtk-uart-apdma.c | 3 +--
1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/drivers/dma/mediatek/mtk-uart-apdma.c b/drivers/dma/mediatek/mtk-uart-apdma.c
index a1517ef1f4a..0acf6a92a4a 100644
--- a/drivers/dma/mediatek/mtk-uart-apdma.c
+++ b/drivers/dma/mediatek/mtk-uart-apdma.c
@@ -451,9 +451,8 @@ static int mtk_uart_apdma_device_pause(struct dma_chan *chan)
mtk_uart_apdma_write(c, VFF_EN, VFF_EN_CLR_B);
mtk_uart_apdma_write(c, VFF_INT_EN, VFF_INT_EN_CLR_B);

- synchronize_irq(c->irq);
-
spin_unlock_irqrestore(&c->vc.lock, flags);
+ synchronize_irq(c->irq);

return 0;
}
--
2.17.1

2023-08-08 19:57:19

by Eugen Hristev

Subject: Re: [PATCH] dmaengine: mediatek: Fix deadlock caused by synchronize_irq()

On 8/6/23 06:25, Duoming Zhou wrote:
> The synchronize_irq(c->irq) will not return until the IRQ handler
> mtk_uart_apdma_irq_handler() is completed. If the synchronize_irq()
> holds a spin_lock and waits the IRQ handler to complete, but the
> IRQ handler also needs the same spin_lock. The deadlock will happen.
> The process is shown below:
>
> cpu0 cpu1
> mtk_uart_apdma_device_pause() | mtk_uart_apdma_irq_handler()
> spin_lock_irqsave() |
> | spin_lock_irqsave()
> //hold the lock to wait |
> synchronize_irq() |
>
> This patch reorders the synchronize_irq(c->irq) outside the spin_lock
> in order to mitigate the bug.
>
> Fixes: 9135408c3ace ("dmaengine: mediatek: Add MediaTek UART APDMA support")
> Signed-off-by: Duoming Zhou <[email protected]>
> ---
> drivers/dma/mediatek/mtk-uart-apdma.c | 3 +--
> 1 file changed, 1 insertion(+), 2 deletions(-)
>
> diff --git a/drivers/dma/mediatek/mtk-uart-apdma.c b/drivers/dma/mediatek/mtk-uart-apdma.c
> index a1517ef1f4a..0acf6a92a4a 100644
> --- a/drivers/dma/mediatek/mtk-uart-apdma.c
> +++ b/drivers/dma/mediatek/mtk-uart-apdma.c
> @@ -451,9 +451,8 @@ static int mtk_uart_apdma_device_pause(struct dma_chan *chan)
> mtk_uart_apdma_write(c, VFF_EN, VFF_EN_CLR_B);
> mtk_uart_apdma_write(c, VFF_INT_EN, VFF_INT_EN_CLR_B);
>
> - synchronize_irq(c->irq);
> -
> spin_unlock_irqrestore(&c->vc.lock, flags);
> + synchronize_irq(c->irq);
>
> return 0;
> }


Reviewed-by: Eugen Hristev <[email protected]>

2023-10-04 14:18:29

by Vinod Koul

Subject: Re: [PATCH] dmaengine: mediatek: Fix deadlock caused by synchronize_irq()

On Sun, 06 Aug 2023 11:25:11 +0800, Duoming Zhou wrote:
> The synchronize_irq(c->irq) will not return until the IRQ handler
> mtk_uart_apdma_irq_handler() is completed. If the synchronize_irq()
> holds a spin_lock and waits the IRQ handler to complete, but the
> IRQ handler also needs the same spin_lock. The deadlock will happen.
> The process is shown below:
>
> cpu0 cpu1
> mtk_uart_apdma_device_pause() | mtk_uart_apdma_irq_handler()
> spin_lock_irqsave() |
> | spin_lock_irqsave()
> //hold the lock to wait |
> synchronize_irq() |
>
> [...]

Applied, thanks!

[1/1] dmaengine: mediatek: Fix deadlock caused by synchronize_irq()
commit: 01f1ae2733e2bb4de92fefcea5fda847d92aede1

Best regards,
--
~Vinod