From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (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 42436168C2 for ; Mon, 8 May 2023 10:20:43 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id AB5D8C433D2; Mon, 8 May 2023 10:20:42 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1683541243; bh=THqKYMfcM+GzOxOsdQYfi9OYkNukoNDkFI2tOAkOM7s=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=TVxafhLU4tnjDCKccE3ZDcoEhddhyrPPz/FdSQARf7RuSdyX9cADwUDTs2IQc6t39 oxsbYCIWhGLdj1p60wcu8mQdsi4KcN1roCQSPcx+zy/4EmRf6a7hifaAsm1jnioMYU dIp9J9cosVDoV3ydRpvvTZzlqWZMQany7PR9ooRo= From: Greg Kroah-Hartman To: stable@vger.kernel.org Cc: Greg Kroah-Hartman , patches@lists.linux.dev, =?UTF-8?q?Ilpo=20J=C3=A4rvinen?= Subject: [PATCH 6.2 051/663] serial: 8250: Fix serial8250_tx_empty() race with DMA Tx Date: Mon, 8 May 2023 11:37:57 +0200 Message-Id: <20230508094430.139158072@linuxfoundation.org> X-Mailer: git-send-email 2.40.1 In-Reply-To: <20230508094428.384831245@linuxfoundation.org> References: <20230508094428.384831245@linuxfoundation.org> User-Agent: quilt/0.67 Precedence: bulk X-Mailing-List: patches@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit From: Ilpo Järvinen commit 146a37e05d620cef4ad430e5d1c9c077fe6fa76f upstream. There's a potential race before THRE/TEMT deasserts when DMA Tx is starting up (or the next batch of continuous Tx is being submitted). This can lead to misdetecting Tx empty condition. It is entirely normal for THRE/TEMT to be set for some time after the DMA Tx had been setup in serial8250_tx_dma(). As Tx side is definitely not empty at that point, it seems incorrect for serial8250_tx_empty() claim Tx is empty. Fix the race by also checking in serial8250_tx_empty() whether there's DMA Tx active. Note: This fix only addresses in-kernel race mainly to make using TCSADRAIN/FLUSH robust. Userspace can still cause other races but they seem userspace concurrency control problems. Fixes: 9ee4b83e51f74 ("serial: 8250: Add support for dmaengine") Cc: stable@vger.kernel.org Signed-off-by: Ilpo Järvinen Link: https://lore.kernel.org/r/20230317113318.31327-3-ilpo.jarvinen@linux.intel.com Signed-off-by: Greg Kroah-Hartman --- drivers/tty/serial/8250/8250.h | 12 ++++++++++++ drivers/tty/serial/8250/8250_port.c | 7 ++++--- 2 files changed, 16 insertions(+), 3 deletions(-) --- a/drivers/tty/serial/8250/8250.h +++ b/drivers/tty/serial/8250/8250.h @@ -365,6 +365,13 @@ static inline void serial8250_do_prepare if (dma->prepare_rx_dma) dma->prepare_rx_dma(p); } + +static inline bool serial8250_tx_dma_running(struct uart_8250_port *p) +{ + struct uart_8250_dma *dma = p->dma; + + return dma && dma->tx_running; +} #else static inline int serial8250_tx_dma(struct uart_8250_port *p) { @@ -380,6 +387,11 @@ static inline int serial8250_request_dma return -1; } static inline void serial8250_release_dma(struct uart_8250_port *p) { } + +static inline bool serial8250_tx_dma_running(struct uart_8250_port *p) +{ + return false; +} #endif static inline int ns16550a_goto_highspeed(struct uart_8250_port *up) --- a/drivers/tty/serial/8250/8250_port.c +++ b/drivers/tty/serial/8250/8250_port.c @@ -2009,18 +2009,19 @@ static int serial8250_tx_threshold_handl static unsigned int serial8250_tx_empty(struct uart_port *port) { struct uart_8250_port *up = up_to_u8250p(port); + unsigned int result = 0; unsigned long flags; - u16 lsr; serial8250_rpm_get(up); spin_lock_irqsave(&port->lock, flags); - lsr = serial_lsr_in(up); + if (!serial8250_tx_dma_running(up) && uart_lsr_tx_empty(serial_lsr_in(up))) + result = TIOCSER_TEMT; spin_unlock_irqrestore(&port->lock, flags); serial8250_rpm_put(up); - return uart_lsr_tx_empty(lsr) ? TIOCSER_TEMT : 0; + return result; } unsigned int serial8250_do_get_mctrl(struct uart_port *port)