Re: [PATCH v4 2/3] serial: core: allow third iteration in uart_get_baud_rate() fallback

[sashiko-bot@kernel.org]

> In uart_get_baud_rate(), when the requested baud rate is out of range
> (try == 0) and old is non-NULL, the function copies the old termios baud
> rate into termios, sets old = NULL, and continues to try == 1. If the
> old baud rate is also out of range (for instance, after uport->uartclk
> was lowered via TIOCSSERIAL so max = uport->uartclk / 16 is smaller than
> both the old and new baud rates), try == 1 clips baud to [min + 1,
> max - 1] and encodes it into termios via tty_termios_encode_baud_rate().
> 
> However, because the loop bound is for (try = 0; try < 2; try++), the
> loop terminates immediately after try == 1 without re-evaluating
> baud = tty_termios_baud_rate(termios) for the clipped rate, hitting
> WARN_ON(1) and returning 0, which then triggers a fatal divide-by-zero
> (Oops: divide error) in uart_get_divisor():
> 
>   WARNING: drivers/tty/serial/serial_core.c:548 at uart_get_baud_rate+0x136/0x260, CPU#1: init/1
> [ ... ]
> Fixes: 091ea8e5d34e ("serial: core: prevent division by zero by always returning non-zero baud rate")
> Cc: stable@vger.kernel.org
> Reviewed-by: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com>
> Assisted-by: LLM
> Signed-off-by: Hui Peng <benquike@gmail.com>

Sashiko has reviewed this patch and found no issues. It looks great!

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Sashiko AI review · https://sashiko.dev/#/patchset/20260924060511.2364717-1-benquike@gmail.com?part=2