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Message-id: <55F27197.8020402@samsung.com>
Date: Fri, 11 Sep 2015 15:15:51 +0900
From: Krzysztof Kozlowski <k.kozlowski@...sung.com>
To: Robert Baldyga <r.baldyga@...sung.com>, gregkh@...uxfoundation.org
Cc: jslaby@...e.com, linux-serial@...r.kernel.org,
linux-kernel@...r.kernel.org, m.szyprowski@...sung.com
Subject: Re: [PATCH v2 3/4] serial: samsung: introduce
s3c24xx_serial_rx_drain_fifo() function
On 10.09.2015 22:41, Robert Baldyga wrote:
> This patch introduces s3c24xx_serial_rx_drain_fifo() which reads data
> from RX FIFO and writes it to tty buffer. It also checks for special
> conditions (such as 'break') and handles it. This function has been
> separated from s3c24xx_serial_rx_chars_pio() as it contains code which
> can be used also in DMA mode.
Much better, thanks! Now it is also easier to spot the difference (see
below).
>
> Signed-off-by: Robert Baldyga <r.baldyga@...sung.com>
> ---
> drivers/tty/serial/samsung.c | 23 +++++++++++++----------
> 1 file changed, 13 insertions(+), 10 deletions(-)
>
> diff --git a/drivers/tty/serial/samsung.c b/drivers/tty/serial/samsung.c
> index dc4be54..1d7dd86 100644
> --- a/drivers/tty/serial/samsung.c
> +++ b/drivers/tty/serial/samsung.c
> @@ -621,16 +621,12 @@ finish:
> return IRQ_HANDLED;
> }
>
> -static irqreturn_t s3c24xx_serial_rx_chars_pio(void *dev_id)
> +static void s3c24xx_serial_rx_drain_fifo(struct s3c24xx_uart_port *ourport)
> {
> - struct s3c24xx_uart_port *ourport = dev_id;
> struct uart_port *port = &ourport->port;
> unsigned int ufcon, ch, flag, ufstat, uerstat;
> - unsigned long flags;
> int max_count = port->fifosize;
>
> - spin_lock_irqsave(&port->lock, flags);
> -
> while (max_count-- > 0) {
> ufcon = rd_regl(port, S3C2410_UFCON);
> ufstat = rd_regl(port, S3C2410_UFSTAT);
> @@ -654,9 +650,7 @@ static irqreturn_t s3c24xx_serial_rx_chars_pio(void *dev_id)
> ufcon |= S3C2410_UFCON_RESETRX;
> wr_regl(port, S3C2410_UFCON, ufcon);
> rx_enabled(port) = 1;
> - spin_unlock_irqrestore(&port->lock,
> - flags);
> - goto out;
> + return;
> }
> continue;
> }
> @@ -702,10 +696,19 @@ static irqreturn_t s3c24xx_serial_rx_chars_pio(void *dev_id)
> ch, flag);
> }
>
> - spin_unlock_irqrestore(&port->lock, flags);
> tty_flip_buffer_push(&port->state->port);
Here is a difference - previously this was outside of spinlock. I think
moving it inside spin lock is okay, just the interrupts won't be
disabled before unlock and queue_work() from tty_flip_buffer_push().
However after testing this patchset (entire) on:
next-20150910 + my dt-for-next branch (dma for serial) + this patchset
you can see quite complicated lockdep warning:
[ 3.568657] =========================================================
[ 3.575079] [ INFO: possible irq lock inversion dependency detected ]
[ 3.581506] 4.2.0-next-20150910-00009-g65fd5a9cff54 #218 Not tainted
[ 3.587838] ---------------------------------------------------------
[ 3.594263] swapper/0/0 just changed the state of lock:
[ 3.599470] (&port_lock_key){..-...}, at: [<c02a8fac>]
s3c24xx_serial_tx_dma_complete+0x8c/0xfc
[ 3.608237] but this lock took another, SOFTIRQ-unsafe lock in the past:
[ 3.614919] (&(&ctx->lock)->rlock){+.+...}
[ 3.614919]
[ 3.614919] and interrupts could create inverse lock ordering between
them.
[ 3.614919]
[ 3.625076]
[ 3.625076] other info that might help us debug this:
[ 3.631586] Possible interrupt unsafe locking scenario:
[ 3.631586]
[ 3.638356] CPU0 CPU1
[ 3.642870] ---- ----
[ 3.647382] lock(&(&ctx->lock)->rlock);
[ 3.651376] local_irq_disable();
[ 3.657278] lock(&port_lock_key);
[ 3.663267] lock(&(&ctx->lock)->rlock);
[ 3.669777] <Interrupt>
[ 3.672381] lock(&port_lock_key);
Config: exynos, disabled MMC_CLKGATE, enabled usual testing stuff
Board: Trats2
Didn't you notice it?
Additionally the SysRq "Show backtrace of all active CPUs" on this
linux-next (without additional patches, pure next) has significant delay
(like 5 seconds) and a:
[ 169.221223] s3c-i2c 138d0000.i2c: timeout waiting for bus idle
That's weird. But as I said this occurs on pure next as well.
Dmesgs and config attached.
Best regards,
Krzysztof
> +}
> +
> +static irqreturn_t s3c24xx_serial_rx_chars_pio(void *dev_id)
> +{
> + struct s3c24xx_uart_port *ourport = dev_id;
> + struct uart_port *port = &ourport->port;
> + unsigned long flags;
> +
> + spin_lock_irqsave(&port->lock, flags);
> + s3c24xx_serial_rx_drain_fifo(ourport);
> + spin_unlock_irqrestore(&port->lock, flags);
>
> -out:
> return IRQ_HANDLED;
> }
>
>
View attachment "trats2-backtrace-stall-dmesg.txt" of type "text/plain" (6459 bytes)
View attachment "trats2-serial-lockdep-issue-config.txt" of type "text/plain" (92777 bytes)
View attachment "trats2-serial-lockdep-issue-dmesg.txt" of type "text/plain" (37811 bytes)
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