Re: [PATCH v2] tty: serial: lpuart: Add port lock for registers read in lpuart32_set_termios()

[sashiko-bot@kernel.org]

> From: Sherry Sun <sherry.sun@nxp.com>
> 
> lpuart32_set_termios() reads UARTCTRL at function entry without holding
> the port lock. lpuart32_console_write() can run concurrently on another
> CPU and temporarily clears the RIE (Receiver Interrupt Enable) bit while
> it polls characters out. If the unlocked read in set_termios lands inside
> that window, the stale snapshot is written back, permanently clearing
> RIE. Once lost, no normal code path re-enables them, so the UART stops
> receiving characters and becomes unresponsive.
> 
> Need to add port lock for the registers read in lpuart32_set_termios() to
> avoid the unlocked snapshot captured. Since neither uart_get_baud_rate()
> nor lpuart_dma_rx_free() uses ctrl, old_ctrl, bd, or modem, the register
> reads and bit manipulations could be moved into the existing
> uart_port_lock_irqsave() critical section after lpuart_dma_rx_free().
> 
> Please note that this only fix the normal printk path, in the
> oops_in_progress path of lpuart32_console_write(), when trylock fails,
> RIE is cleared and old_cr restored without the port lock held, there is
> still a risk of stale snapshot, but it's acceptable for the post-oops
> state and the trylock-fail window.
> 
> Fixes: 380c966c093e ("tty: serial: fsl_lpuart: add 32-bit register interface support")
> Signed-off-by: Sherry Sun <sherry.sun@nxp.com>

Sashiko has reviewed this patch and found no issues.

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Sashiko AI review · https://sashiko.dev/#/patchset/20261112-lpuart_port_lock-v2-1-e1d914e52660@nxp.com?part=1