Messages in this thread Patch in this message | | | From | John Ogness <> | Subject | [PATCH tty v1 5/8] serial: 8250: lock port for rx_dma() callback | Date | Thu, 25 May 2023 11:37:56 +0206 |
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The rx_dma() callback (omap_8250_rx_dma) accesses UART_IER. This register is modified twice by each console write (serial8250_console_write()) under the port lock. However, not all calls to the rx_dma() callback are under the port lock.
Add the missing port locking around rx_dma() callback calls. Add lockdep notation to the omap_8250_rx_dma().
Note that this is not fixing a real problem because:
1. Currently DMA is forced off for 8250_omap consoles.
2. The serial devices are resumed before console printing is enabled.
However, adding this locking allows for clean locking semantics for the rx_dma() callback so that lockdep can be used to identify possible problems in the future. It also simplifies synchronization of UART_IER in general by not needing to rely on implementation details such as 1 and 2.
Signed-off-by: John Ogness <john.ogness@linutronix.de> --- drivers/tty/serial/8250/8250_omap.c | 13 +++++++++++-- 1 file changed, 11 insertions(+), 2 deletions(-)
diff --git a/drivers/tty/serial/8250/8250_omap.c b/drivers/tty/serial/8250/8250_omap.c index c17d98161d5e..3cb9cfa62331 100644 --- a/drivers/tty/serial/8250/8250_omap.c +++ b/drivers/tty/serial/8250/8250_omap.c @@ -728,8 +728,11 @@ static int omap_8250_startup(struct uart_port *port) priv->wer |= OMAP_UART_TX_WAKEUP_EN; serial_out(up, UART_OMAP_WER, priv->wer); - if (up->dma && !(priv->habit & UART_HAS_EFR2)) + if (up->dma && !(priv->habit & UART_HAS_EFR2)) { + spin_lock_irq(&port->lock); up->dma->rx_dma(up); + spin_unlock_irq(&port->lock); + } enable_irq(up->port.irq); @@ -1003,6 +1006,9 @@ static int omap_8250_rx_dma(struct uart_8250_port *p) unsigned long flags; u32 reg; + /* Port locked to synchronize UART_IER access against the console. */ + lockdep_assert_held_once(&p->port.lock); + if (priv->rx_dma_broken) return -EINVAL; @@ -1736,8 +1742,11 @@ static int omap8250_runtime_resume(struct device *dev) if (up && omap8250_lost_context(up)) omap8250_restore_regs(up); - if (up && up->dma && up->dma->rxchan && !(priv->habit & UART_HAS_EFR2)) + if (up && up->dma && up->dma->rxchan && !(priv->habit & UART_HAS_EFR2)) { + spin_lock_irq(&up->port.lock); omap_8250_rx_dma(up); + spin_unlock_irq(&up->port.lock); + } priv->latency = priv->calc_latency; schedule_work(&priv->qos_work); -- 2.30.2
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