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tty: serial: samsung: Remove redundant port lock acquisition in rx helpers 

Sashiko identified a deadlock when the console flow is engaged [1].

When console flow control is enabled (UPF_CONS_FLOW),
s3c24xx_serial_stop_tx() calls s3c24xx_serial_rx_enable() and
s3c24xx_serial_start_tx() calls s3c24xx_serial_rx_disable().

The serial core framework invokes the .stop_tx() and .start_tx()
callbacks with the port->lock spinlock already held. Furthermore, all
internal driver paths that invoke stop_tx (such as the DMA TX
completion handler s3c24xx_serial_tx_dma_complete() or the PIO TX IRQ
handler s3c24xx_serial_tx_irq()) also acquire port->lock prior to
calling it. (Note that s3c24xx_serial_start_tx() is only invoked by the
serial core).

However, s3c24xx_serial_rx_enable() and s3c24xx_serial_rx_disable()
unconditionally attempt to acquire port->lock again using
uart_port_lock_irqsave(). Since spinlocks are not recursive, this
causes a deadlock on the same CPU when console flow control is engaged.

Remove the redundant lock acquisition from both rx helper functions.

Cc: stable <stable@kernel.org>
Fixes: b497549a03 ("[ARM] S3C24XX: Split serial driver into core and per-cpu drivers")
Reported-by: John Ogness <john.ogness@linutronix.de>
Closes: https://sashiko.dev/#/patchset/20260506121606.5805-1-john.ogness%40linutronix.de [1]
Signed-off-by: Tudor Ambarus <tudor.ambarus@linaro.org>
Link: https://patch.msgid.link/20260515-samsung-tty-flow-control-deadlock-v1-1-93255edbc9bc@linaro.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
master
Tudor Ambarus 2026-05-15 12:41:21 +00:00 committed by Greg Kroah-Hartman
parent ea66be25f0
commit a3bb136bff
1 changed files with 0 additions and 8 deletions
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8
drivers/tty/serial/samsung_tty.c
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@ -245,12 +245,9 @@ static bool s3c24xx_serial_txempty_nofifo(const struct uart_port *port)
static void s3c24xx_serial_rx_enable(struct uart_port *port)
{
struct s3c24xx_uart_port *ourport = to_ourport(port);
unsigned long flags;
int count = 10000;
u32 ucon, ufcon;
uart_port_lock_irqsave(port, &flags);
while (--count && !s3c24xx_serial_txempty_nofifo(port))
udelay(100);
@ -263,23 +260,18 @@ static void s3c24xx_serial_rx_enable(struct uart_port *port)
wr_regl(port, S3C2410_UCON, ucon);
ourport->rx_enabled = 1;
uart_port_unlock_irqrestore(port, flags);
}
static void s3c24xx_serial_rx_disable(struct uart_port *port)
{
struct s3c24xx_uart_port *ourport = to_ourport(port);
unsigned long flags;
u32 ucon;
uart_port_lock_irqsave(port, &flags);
ucon = rd_regl(port, S3C2410_UCON);
ucon &= ~S3C2410_UCON_RXIRQMODE;
wr_regl(port, S3C2410_UCON, ucon);
ourport->rx_enabled = 0;
uart_port_unlock_irqrestore(port, flags);
}
static void s3c24xx_serial_stop_tx(struct uart_port *port)