linux-kernel - Re: [PATCH] serial: 8250: fix panic due to PSLVERR

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Message-ID: <84iknl5uex.fsf@jogness.linutronix.de>
Date: Thu, 03 Apr 2025 14:03:58 +0206
From: John Ogness <john.ogness@...utronix.de>
To: Yunhui Cui <cuiyunhui@...edance.com>, gregkh@...uxfoundation.org,
 jirislaby@...nel.org, pmladek@...e.com, arnd@...db.de,
 andriy.shevchenko@...ux.intel.com, namcao@...utronix.de,
 benjamin.larsson@...exis.eu, schnelle@...ux.ibm.com,
 linux-kernel@...r.kernel.org, linux-serial@...r.kernel.org
Cc: Yunhui Cui <cuiyunhui@...edance.com>
Subject: Re: [PATCH] serial: 8250: fix panic due to PSLVERR

On 2025-04-03, Yunhui Cui <cuiyunhui@...edance.com> wrote:
> When the PSLVERR_RESP_EN parameter is set to 1, the device generates
> an error response if an attempt is made to read an empty RBR (Receive
> Buffer Register) while the FIFO is enabled.
>
> In serial8250_do_startup, calling serial_port_out(port, UART_LCR,
> UART_LCR_WLEN8) triggers dw8250_check_lcr(), which invokes
> dw8250_force_idle() and serial8250_clear_and_reinit_fifos(). The latter
> function enables the FIFO via serial_out(p, UART_FCR, p->fcr).
> Execution proceeds to the dont_test_tx_en label:
> ...
> serial_port_in(port, UART_RX);
> This satisfies the PSLVERR trigger condition.
>
> Because another CPU(e.g., using printk) is accessing the UART (UART
> is busy), the current CPU fails the check (value & ~UART_LCR_SPAR) ==
> (lcr & ~UART_LCR_SPAR), causing it to enter dw8250_force_idle().

Didn't this[0] patch resolve this exact issue?

John Ogness

[0] https://lore.kernel.org/lkml/20220713131722.2316829-1-vamshigajjela@google.com