56 lines
2.2 KiB
Diff
56 lines
2.2 KiB
Diff
From c0bcd8c710c48ab93f0b72c1a3611c39a68c3a74 Mon Sep 17 00:00:00 2001
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From: Yunhui Cui <cuiyunhui@bytedance.com>
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Date: Wed, 23 Jul 2025 10:33:22 +0800
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Subject: serial: 8250: fix panic due to PSLVERR
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When the PSLVERR_RESP_EN parameter is set to 1, the device generates
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an error response if an attempt is made to read an empty RBR (Receive
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Buffer Register) while the FIFO is enabled.
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In serial8250_do_startup(), calling serial_port_out(port, UART_LCR,
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UART_LCR_WLEN8) triggers dw8250_check_lcr(), which invokes
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dw8250_force_idle() and serial8250_clear_and_reinit_fifos(). The latter
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function enables the FIFO via serial_out(p, UART_FCR, p->fcr).
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Execution proceeds to the serial_port_in(port, UART_RX).
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This satisfies the PSLVERR trigger condition.
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When another CPU (e.g., using printk()) is accessing the UART (UART
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is busy), the current CPU fails the check (value & ~UART_LCR_SPAR) ==
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(lcr & ~UART_LCR_SPAR) in dw8250_check_lcr(), causing it to enter
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dw8250_force_idle().
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Put serial_port_out(port, UART_LCR, UART_LCR_WLEN8) under the port->lock
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to fix this issue.
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Panic backtrace:
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[ 0.442336] Oops - unknown exception [#1]
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[ 0.442343] epc : dw8250_serial_in32+0x1e/0x4a
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[ 0.442351] ra : serial8250_do_startup+0x2c8/0x88e
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...
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[ 0.442416] console_on_rootfs+0x26/0x70
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Fixes: c49436b657d0 ("serial: 8250_dw: Improve unwritable LCR workaround")
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Link: https://lore.kernel.org/all/84cydt5peu.fsf@jogness.linutronix.de/T/
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Signed-off-by: Yunhui Cui <cuiyunhui@bytedance.com>
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Reviewed-by: John Ogness <john.ogness@linutronix.de>
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Cc: stable <stable@kernel.org>
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Link: https://lore.kernel.org/r/20250723023322.464-2-cuiyunhui@bytedance.com
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Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
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---
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drivers/tty/serial/8250/8250_port.c | 2 +-
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1 file changed, 1 insertion(+), 1 deletion(-)
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--- a/drivers/tty/serial/8250/8250_port.c
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+++ b/drivers/tty/serial/8250/8250_port.c
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@@ -2376,9 +2376,9 @@ int serial8250_do_startup(struct uart_po
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/*
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* Now, initialize the UART
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*/
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+ uart_port_lock_irqsave(port, &flags);
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serial_port_out(port, UART_LCR, UART_LCR_WLEN8);
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- uart_port_lock_irqsave(port, &flags);
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if (up->port.flags & UPF_FOURPORT) {
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if (!up->port.irq)
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up->port.mctrl |= TIOCM_OUT1;
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