linux-kernel - Re: [PATCH 2/3] serial: 8250_dw: Take port lock while accessing LSR

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Message-ID: <YqmvTrV3o9CfgBbx@smile.fi.intel.com>
Date:   Wed, 15 Jun 2022 13:07:10 +0300
From:   Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
To:     Ilpo Järvinen <ilpo.jarvinen@...ux.intel.com>
Cc:     linux-serial@...r.kernel.org, Greg KH <gregkh@...uxfoundation.org>,
        Jiri Slaby <jirislaby@...nel.org>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/3] serial: 8250_dw: Take port lock while accessing LSR

On Wed, Jun 15, 2022 at 12:06:50PM +0300, Ilpo Järvinen wrote:
> Accessing LSR requires port lock because it mutates lsr_saved_flags
> in serial_lsr_in().

I got this as patch 2/3, where are the 1/3 and 3/3?

...

> @@ -266,7 +266,10 @@ static int dw8250_handle_irq(struct uart_port *p)
>  
>  	/* Manually stop the Rx DMA transfer when acting as flow controller */
>  	if (quirks & DW_UART_QUIRK_IS_DMA_FC && up->dma && up->dma->rx_running && rx_timeout) {
> +		spin_lock_irqsave(&p->lock, flags);
>  		status = serial_lsr_in(up);
> +		spin_unlock_irqrestore(&p->lock, flags);

This reminds me the question, why do we need to save flags here? Aren't we in
IRQ context already? (Perhaps another patch might be issued.)

-- 
With Best Regards,
Andy Shevchenko