linux-kernel - Re: [PATCH 01/26] tty: mxser: drop low-latency workaround

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Message-ID: <0b470bd2-742f-0588-83e0-8a6748b37f7a@kernel.org>
Date:   Thu, 22 Apr 2021 07:59:30 +0200
From:   Jiri Slaby <jirislaby@...nel.org>
To:     Johan Hovold <johan@...nel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:     linux-serial@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 01/26] tty: mxser: drop low-latency workaround

On 21. 04. 21, 11:54, Johan Hovold wrote:
> Commit 67d2bc58afdd ("Char: mxser_new, fix recursive locking") worked
> around the infamous low_latency behaviour of tty_flip_buffer_push() by
> simply dropping and reacquiring the port lock in the interrupt handler.
> 
> Since commit a9c3f68f3cd8 ("tty: Fix low_latency BUG"),
> tty_flip_buffer_push() always schedules a work item to push data to the
> line discipline and there's no need to keep any low_latency hacks around.
> 
> Link: https://lore.kernel.org/lkml/3018694794025219@wsc.cz/T/#m06b04c640a7b6f41afb3d34a4cf29b1df4935d3a
> Signed-off-by: Johan Hovold <johan@...nel.org>

Reviewed-by: Jiri Slaby <jirislaby@...nel.org>

> ---
>   drivers/tty/mxser.c | 7 -------
>   1 file changed, 7 deletions(-)
> 
> diff --git a/drivers/tty/mxser.c b/drivers/tty/mxser.c
> index 2d8e76263a25..16a852ecbe8a 100644
> --- a/drivers/tty/mxser.c
> +++ b/drivers/tty/mxser.c
> @@ -2155,14 +2155,7 @@ static void mxser_receive_chars(struct tty_struct *tty,
>   	port->mon_data.rxcnt += cnt;
>   	port->mon_data.up_rxcnt += cnt;
>   
> -	/*
> -	 * We are called from an interrupt context with &port->slock
> -	 * being held. Drop it temporarily in order to prevent
> -	 * recursive locking.
> -	 */
> -	spin_unlock(&port->slock);
>   	tty_flip_buffer_push(&port->port);
> -	spin_lock(&port->slock);
>   }
>   
>   static void mxser_transmit_chars(struct tty_struct *tty, struct mxser_port *port)
> 

thanks,
-- 
js