This is a note to let you know that I've just added the patch titled
dmaengine: mediatek: Fix deadlock caused by synchronize_irq()
to the 5.4-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
dmaengine-mediatek-fix-deadlock-caused-by-synchroniz.patch
and it can be found in the queue-5.4 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
commit 41e1fbc8638874fd704baa98397edebf23131874
Author: Duoming Zhou <duoming@xxxxxxxxxx>
Date: Sun Aug 6 11:25:11 2023 +0800
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@xxxxxxxxxx>
Reviewed-by: Eugen Hristev <eugen.hristev@xxxxxxxxxxxxx>
Link: https://lore.kernel.org/r/20230806032511.45263-1-duoming@xxxxxxxxxx
Signed-off-by: Vinod Koul <vkoul@xxxxxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
diff --git a/drivers/dma/mediatek/mtk-uart-apdma.c b/drivers/dma/mediatek/mtk-uart-apdma.c
index 7718d09e3d29f..5d1ba3ba3755a 100644
--- a/drivers/dma/mediatek/mtk-uart-apdma.c
+++ b/drivers/dma/mediatek/mtk-uart-apdma.c
@@ -450,9 +450,8 @@ 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;
}
