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Commit e8ffbb71f783 ("serial: 8250: use THRE & __stop_tx also with
DMA") changed __dma_tx_complete() to enable THRI that is cleared in
__stop_tx() once THRE is asserted as UART runs out bits to transmit. It
is possible, however, that more data arrives in between in which case
serial8250_tx_dma() resumes Tx. THRI is not supposed to be on during
DMA Tx because DMA is based on completion handler, therefore THRI must
be cleared unconditionally in serial8250_tx_dma().
When Tx is about to start, another race window exists with
serial8250_handle_irq() leading to a call into __stop_tx() while the
Tx has already been resumed:
__tx_complete():
-> spin_lock(port->lock)
-> dma->tx_running = 0
-> serial8250_set_THRI()
-> spin_unlock(port->lock)
uart_start():
serial8250_handle_irq():
-> spin_lock(port->lock)
-> serial8250_tx_dma():
-> dma->tx_running = 1
-> spin_unlock(port->lock)
-> spin_lock(port->lock)
-> __stop_tx()
Close this race by checking !dma->tx_running before calling into
__stop_tx().
Fixes: e8ffbb71f783 ("serial: 8250: use THRE & __stop_tx also with DMA")
Signed-off-by: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com>
Link: https://lore.kernel.org/r/20220615090651.15340-2-ilpo.jarvinen@linux.intel.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
f8d6e9d3ca