diff options
| author | Ilpo Järvinen <ilpo.jarvinen@linux.intel.com> | 2022-06-15 12:06:49 +0300 |
|---|---|---|
| committer | Greg Kroah-Hartman <gregkh@linuxfoundation.org> | 2022-06-27 14:47:57 +0200 |
| commit | f8d6e9d3ca5c68e24dd485132a93d49abd444eaf (patch) | |
| tree | ab9539c618d9e220a6aba18ea876765d0d74da38 /drivers/tty | |
| parent | 211565b100993c90b53bf40851eacaefc830cfe0 (diff) | |
serial: 8250: Fix __stop_tx() & DMA Tx restart races
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>
Diffstat (limited to 'drivers/tty')
| -rw-r--r-- | drivers/tty/serial/8250/8250_dma.c | 6 | ||||
| -rw-r--r-- | drivers/tty/serial/8250/8250_port.c | 2 |
2 files changed, 4 insertions, 4 deletions
diff --git a/drivers/tty/serial/8250/8250_dma.c b/drivers/tty/serial/8250/8250_dma.c index 7133fceed35e..a8dba4a0a8fb 100644 --- a/drivers/tty/serial/8250/8250_dma.c +++ b/drivers/tty/serial/8250/8250_dma.c @@ -106,10 +106,10 @@ int serial8250_tx_dma(struct uart_8250_port *p) UART_XMIT_SIZE, DMA_TO_DEVICE); dma_async_issue_pending(dma->txchan); - if (dma->tx_err) { + serial8250_clear_THRI(p); + if (dma->tx_err) dma->tx_err = 0; - serial8250_clear_THRI(p); - } + return 0; err: dma->tx_err = 1; diff --git a/drivers/tty/serial/8250/8250_port.c b/drivers/tty/serial/8250/8250_port.c index 8f32fe9e149e..b9cdc5552b0d 100644 --- a/drivers/tty/serial/8250/8250_port.c +++ b/drivers/tty/serial/8250/8250_port.c @@ -1949,7 +1949,7 @@ int serial8250_handle_irq(struct uart_port *port, unsigned int iir) if ((status & UART_LSR_THRE) && (up->ier & UART_IER_THRI)) { if (!up->dma || up->dma->tx_err) serial8250_tx_chars(up); - else + else if (!up->dma->tx_running) __stop_tx(up); } |