diff options
| author | Raul E Rangel <rrangel@chromium.org> | 2026-02-09 23:58:18 +0300 |
|---|---|---|
| committer | Greg Kroah-Hartman <gregkh@linuxfoundation.org> | 2026-03-12 17:29:59 +0300 |
| commit | a424a34b8faddf97b5af41689087e7a230f79ba7 (patch) | |
| tree | d50fd9b76d7f2907e13d8eaaa6367468f0b22d6c | |
| parent | 1f318b96cc84d7c2ab792fcc0bfd42a7ca890681 (diff) | |
| download | linux-a424a34b8faddf97b5af41689087e7a230f79ba7.tar.xz | |
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.
Fixes: 9e512eaaf8f4 ("serial: 8250: Fix fifo underflow on flush")
Cc: stable <stable@kernel.org>
Signed-off-by: Raul E Rangel <rrangel@google.com>
Link: https://patch.msgid.link/20260209135815.1.I16366ecb0f62f3c96fe3dd5763fcf6f3c2b4d8cd@changeid
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
| -rw-r--r-- | drivers/tty/serial/8250/8250_dma.c | 15 |
1 files changed, 15 insertions, 0 deletions
diff --git a/drivers/tty/serial/8250/8250_dma.c b/drivers/tty/serial/8250/8250_dma.c index bdd26c9f34bd..3b6452e759d5 100644 --- a/drivers/tty/serial/8250/8250_dma.c +++ b/drivers/tty/serial/8250/8250_dma.c @@ -162,7 +162,22 @@ void serial8250_tx_dma_flush(struct uart_8250_port *p) */ dma->tx_size = 0; + /* + * We can't use `dmaengine_terminate_sync` because `uart_flush_buffer` is + * holding the uart port spinlock. + */ dmaengine_terminate_async(dma->txchan); + + /* + * The callback might or might not run. If it doesn't run, we need to ensure + * that `tx_running` is cleared so that we can schedule new transactions. + * If it does run, then the zombie callback will clear `tx_running` again + * and perform a no-op since `tx_size` was cleared above. + * + * In either case, we ASSUME the DMA transaction will terminate before we + * issue a new `serial8250_tx_dma`. + */ + dma->tx_running = 0; } int serial8250_rx_dma(struct uart_8250_port *p) |