diff options
| author | Tudor Ambarus <tudor.ambarus@linaro.org> | 2026-05-15 12:41:21 +0000 |
|---|---|---|
| committer | Greg Kroah-Hartman <gregkh@linuxfoundation.org> | 2026-05-22 11:48:38 +0200 |
| commit | a3bb136bff5e6a5e48cdd813246c9c4686feaaa9 (patch) | |
| tree | 4ffc6c4e5ec31c5668e5a694410599ff623a3da7 /drivers/tty/serial | |
| parent | ea66be25f0e934f49d24cd0c5845d13cdba3520b (diff) | |
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: b497549a035c ("[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>
Diffstat (limited to 'drivers/tty/serial')
| -rw-r--r-- | drivers/tty/serial/samsung_tty.c | 8 |
1 files changed, 0 insertions, 8 deletions
diff --git a/drivers/tty/serial/samsung_tty.c b/drivers/tty/serial/samsung_tty.c index e27806bf2cf3..17cd5bb100b1 100644 --- a/drivers/tty/serial/samsung_tty.c +++ b/drivers/tty/serial/samsung_tty.c @@ -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) |