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

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Message-Id: <20210421095509.3024-2-johan@kernel.org>
Date:   Wed, 21 Apr 2021 11:54:44 +0200
From:   Johan Hovold <johan@...nel.org>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:     Jiri Slaby <jirislaby@...nel.org>, linux-serial@...r.kernel.org,
        linux-kernel@...r.kernel.org, Johan Hovold <johan@...nel.org>
Subject: [PATCH 01/26] tty: mxser: drop low-latency workaround

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>
---
 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)
-- 
2.26.3