serial: 8250: Fix thread unsafe __dma_tx_complete function
serial: 8250: Fix thread unsafe __dma_tx_complete function

__dma_tx_complete is not protected against concurrent
call of serial8250_tx_dma. it can lead to circular tail
index corruption or parallel call of serial_tx_dma on the
same data portion.

This patch fixes this issue by holding the port lock.

Signed-off-by: Loic Poulain <7dbc6498a90ff1ada42fc224430b4f763baa5c5c@intel.com>
Reviewed-by: Heikki Krogerus <0364a60538b3766c953bdea7e7e4859afd98436c@linux.intel.com>
Cc: stable <4fbacc2fa0ffdbb11bf1ad6925b886ebd08dd15f@vger.kernel.org>
Signed-off-by: Greg Kroah-Hartman <4645f7897fd33786a2ee1264d590b3c400559d85@linuxfoundation.org>

KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs