From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id E221B403EB6 for ; Thu, 4 Jun 2026 10:44:23 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1780569864; cv=none; b=XwdsMADye1jEwlfQuczMG8gWEOOXPRk64x/u9WhlXttdErCNEplXPVG/1In6ds2AiTL2BnlFDarF6P0s6LQH7sO5LPnVaeyA+uMq9B2dCTPw8rGhrsuP5dky87QrG7VziAKRQYCxfd3CdaELoreBCB6ld+us5L3i4YZSFD3kQOQ= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1780569864; c=relaxed/simple; bh=xqn3VHtILWo3pEjX9QbfE7ISawsBrpI8MyZw2w+s2nY=; h=Subject:To:Cc:From:Date:Message-ID:MIME-Version:Content-Type; b=qkIdLeVqkNJ/36uEmb8N5Z1GxllQgZtbQM+rPQ5TAgOcDwB+yecqWyWuSdoQPeQXTH2Koc5W0gzoIHiqCPLx56NWsepbDjNqtNucCz5h2nh10wmJhve1O22ZLLTsOT3mcQYX6dwjbl55E/RWYZ12KvwlHmRHyuP5O7dLrufEnFs= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b=h3gBdck2; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b="h3gBdck2" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 0CB171F00893; Thu, 4 Jun 2026 10:44:22 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linuxfoundation.org; s=korg; t=1780569863; bh=sBNj1I6cu9w+/sGKQ8VfOFWWDFww5oVNC42tJo/zGUw=; h=Subject:To:Cc:From:Date; b=h3gBdck2Y4KpzhL+UpjaPHgowuxLjmQFNljXC8bX+Yx+WpAGxf820IBzkKnR1O8tG d6TGHC8nX1r08HR/jZHJoACNriBUiGVj4NfqKWqEtrxHTnJGpHoN8ru/l0BHKLgF5h 7sRHuzn7i4q06Qy3CetRv7U7HLJnHPfzZKSOTog0= Subject: FAILED: patch "[PATCH] tty: serial: samsung: Remove redundant port lock acquisition" failed to apply to 5.15-stable tree To: tudor.ambarus@linaro.org,gregkh@linuxfoundation.org,john.ogness@linutronix.de,stable@kernel.org Cc: From: Date: Thu, 04 Jun 2026 12:41:29 +0200 Message-ID: <2026060429-saddling-hacked-b97c@gregkh> Precedence: bulk X-Mailing-List: stable@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=ANSI_X3.4-1968 Content-Transfer-Encoding: 8bit The patch below does not apply to the 5.15-stable tree. If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to . To reproduce the conflict and resubmit, you may use the following commands: git fetch https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/ linux-5.15.y git checkout FETCH_HEAD git cherry-pick -x a3bb136bff5e6a5e48cdd813246c9c4686feaaa9 # git commit -s git send-email --to '' --in-reply-to '2026060429-saddling-hacked-b97c@gregkh' --subject-prefix 'PATCH 5.15.y' HEAD^.. Possible dependencies: thanks, greg k-h ------------------ original commit in Linus's tree ------------------ >From a3bb136bff5e6a5e48cdd813246c9c4686feaaa9 Mon Sep 17 00:00:00 2001 From: Tudor Ambarus Date: Fri, 15 May 2026 12:41:21 +0000 Subject: [PATCH] tty: serial: samsung: Remove redundant port lock acquisition in rx helpers Sashiko identified a deadlock when the console flow is engaged [1]. When console flow control is enabled (UPF_CONS_FLOW), s3c24xx_serial_stop_tx() calls s3c24xx_serial_rx_enable() and s3c24xx_serial_start_tx() calls s3c24xx_serial_rx_disable(). The serial core framework invokes the .stop_tx() and .start_tx() callbacks with the port->lock spinlock already held. Furthermore, all internal driver paths that invoke stop_tx (such as the DMA TX completion handler s3c24xx_serial_tx_dma_complete() or the PIO TX IRQ handler s3c24xx_serial_tx_irq()) also acquire port->lock prior to calling it. (Note that s3c24xx_serial_start_tx() is only invoked by the serial core). However, s3c24xx_serial_rx_enable() and s3c24xx_serial_rx_disable() unconditionally attempt to acquire port->lock again using uart_port_lock_irqsave(). Since spinlocks are not recursive, this causes a deadlock on the same CPU when console flow control is engaged. Remove the redundant lock acquisition from both rx helper functions. Cc: stable Fixes: b497549a035c ("[ARM] S3C24XX: Split serial driver into core and per-cpu drivers") Reported-by: John Ogness Closes: https://sashiko.dev/#/patchset/20260506121606.5805-1-john.ogness%40linutronix.de [1] Signed-off-by: Tudor Ambarus Link: https://patch.msgid.link/20260515-samsung-tty-flow-control-deadlock-v1-1-93255edbc9bc@linaro.org Signed-off-by: Greg Kroah-Hartman diff --git a/drivers/tty/serial/samsung_tty.c b/drivers/tty/serial/samsung_tty.c index e27806bf2cf3..17cd5bb100b1 100644 --- a/drivers/tty/serial/samsung_tty.c +++ b/drivers/tty/serial/samsung_tty.c @@ -245,12 +245,9 @@ static bool s3c24xx_serial_txempty_nofifo(const struct uart_port *port) static void s3c24xx_serial_rx_enable(struct uart_port *port) { struct s3c24xx_uart_port *ourport = to_ourport(port); - unsigned long flags; int count = 10000; u32 ucon, ufcon; - uart_port_lock_irqsave(port, &flags); - while (--count && !s3c24xx_serial_txempty_nofifo(port)) udelay(100); @@ -263,23 +260,18 @@ static void s3c24xx_serial_rx_enable(struct uart_port *port) wr_regl(port, S3C2410_UCON, ucon); ourport->rx_enabled = 1; - uart_port_unlock_irqrestore(port, flags); } static void s3c24xx_serial_rx_disable(struct uart_port *port) { struct s3c24xx_uart_port *ourport = to_ourport(port); - unsigned long flags; u32 ucon; - uart_port_lock_irqsave(port, &flags); - ucon = rd_regl(port, S3C2410_UCON); ucon &= ~S3C2410_UCON_RXIRQMODE; wr_regl(port, S3C2410_UCON, ucon); ourport->rx_enabled = 0; - uart_port_unlock_irqrestore(port, flags); } static void s3c24xx_serial_stop_tx(struct uart_port *port)