dmaengine: mediatek: Fix deadlock caused by synchronize_irq()

[ Upstream commit 01f1ae2733e2bb4de92fefcea5fda847d92aede1 ]

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 <duoming@zju.edu.cn>
Reviewed-by: Eugen Hristev <eugen.hristev@collabora.com>
Link: https://lore.kernel.org/r/20230806032511.45263-1-duoming@zju.edu.cn
Signed-off-by: Vinod Koul <vkoul@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>

diff --git a/drivers/dma/mediatek/mtk-uart-apdma.c b/drivers/dma/mediatek/mtk-uart-apdma.c
index a1517ef1f4a0185700343797ef05d8ef6810ed0a..0acf6a92a4ad39952123f92df12e3af51ea5a746 100644 (file)
--- 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;
 }