Re: [PATCH] tty: serial: fsl_lpuart: fix del_timer_sync() vs timer routine deadlock
From: Stefan Agner <stefan@agner.ch>
Date: 2016-12-02 18:14:24
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lkml
On 2016-12-02 02:28, Nikita Yushchenko wrote:
Problem found via lockdep: - lpuart_set_termios() calls del_timer_sync(&sport->lpuart_timer) while holding sport->port.lock - sport->lpuart_timer routine is lpuart_timer_func() that calls lpuart_copy_rx_to_tty() that acquires same lock. To fix, move Rx DMA stopping out of lock, as it already is in other places in the same file. While at it, also make Rx DMA start/stop code to look the same is in other places in the same file.
Yeah I saw that too, never really came around to look closer into it. Thanks for looking into it. You removed the check whether there was an old configuration, I think the idea of that was that we only resize DMA if it was configured differently before... Not sure how startup/set_termios calls are ordered. I guess in practice that shouldn't really make a difference since lpuart_dma_rx_use can't be true until after startup? One nit below. -- Stefan
quoted hunk ↗ jump to hunk
Signed-off-by: Nikita Yushchenko <nikita.yoush@cogentembedded.com> --- drivers/tty/serial/fsl_lpuart.c | 25 ++++++++++++++----------- 1 file changed, 14 insertions(+), 11 deletions(-)diff --git a/drivers/tty/serial/fsl_lpuart.c b/drivers/tty/serial/fsl_lpuart.c index a1c6519837a4..81100c40f33b 100644 --- a/drivers/tty/serial/fsl_lpuart.c +++ b/drivers/tty/serial/fsl_lpuart.c@@ -1407,6 +1407,18 @@ lpuart_set_termios(struct uart_port *port,struct ktermios *termios, /* ask the core to calculate the divisor */ baud = uart_get_baud_rate(port, termios, old, 50, port->uartclk / 16); + /* + * Need to update the Ring buffer length according to the selected + * baud rate and restart Rx DMA path. + * + * Since timer function acqures sport->port.lock, need to stop before + * acquring same lock because otherwise del_timer_sync() can deadlock. + */ + if (sport->lpuart_dma_rx_use) { + del_timer_sync(&sport->lpuart_timer); + lpuart_dma_rx_free(&sport->port); + } + spin_lock_irqsave(&sport->port.lock, flags); sport->port.read_status_mask = 0;@@ -1456,17 +1468,8 @@ lpuart_set_termios(struct uart_port *port,struct ktermios *termios, /* restore control register */ writeb(old_cr2, sport->port.membase + UARTCR2); - /* - * If new baud rate is set, we will also need to update the Ring buffer - * length according to the selected baud rate and restart Rx DMA path. - */ - if (old) { - if (sport->lpuart_dma_rx_use) { - del_timer_sync(&sport->lpuart_timer); - lpuart_dma_rx_free(&sport->port); - } - - if (sport->dma_rx_chan && !lpuart_start_rx_dma(sport)) { + if (sport->lpuart_dma_rx_use) { + if (!lpuart_start_rx_dma(sport)) { sport->lpuart_dma_rx_use = true;
No need to set to true here, it is guaranteed to be true at this point.
rx_dma_timer_init(sport);
} else {