In the Linux kernel, the following vulnerability has been resolved: serial: 8250: Fix TX deadlock when using DMA dmaengine_terminate_async does not guarantee that the __dma_tx_complete callback will run. The callback is currently the only place where dma-tx_running gets cleared. If the transaction is canceled and the callback never runs, then dma-tx_running will never get cleared and we will never schedule new TX DMA transactions again.

This change makes it so we clear dma-tx_running after we terminate the DMA transaction. This is "safe" because serial8250_tx_dma_flush is holding the UART port lock. The first thing the callback does is also grab the UART port lock, so access to dma-tx_running is serialized.