From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-14.0 required=3.0 tests=BAYES_00,INCLUDES_CR_TRAILER, INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id ADF78C4361B for ; Wed, 9 Dec 2020 11:23:29 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 78FF32343F for ; Wed, 9 Dec 2020 11:23:29 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1730566AbgLILX3 (ORCPT ); Wed, 9 Dec 2020 06:23:29 -0500 Received: from mail-lf1-f67.google.com ([209.85.167.67]:36653 "EHLO mail-lf1-f67.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727221AbgLILX1 (ORCPT ); Wed, 9 Dec 2020 06:23:27 -0500 Received: by mail-lf1-f67.google.com with SMTP id a8so2599919lfb.3 for ; Wed, 09 Dec 2020 03:23:11 -0800 (PST) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:date:from:to:cc:subject:message-id:references :mime-version:content-disposition:in-reply-to; bh=5e2aSFjarWQkLVbbkT+U1TSmzSIUt4+5IUsX9H9cmb0=; b=SAMgBYhx3vK2pyWxeKfGlKLph7mHrqKfpQWNEiSSpu9KpQqP7x3eM3yH91To7m6qW9 0dOxQb2CNvM+V3RLTzee8LWYwLaOk0CZ0EAH4Rzmsf3m2bRYlwgoPi+ILHPefwWE8Xok /i844AxU0KoChSkEqNz+2fKVf1A2gEeDdMJtqo/WGGtsGwIiW3yzNeRLRKwZs/XSPXdd LQ6qWqYKdrfe4LLrBHV6Mft4UPpasD1YoTUxnT0gpzmk87MZsNbEVWfXdLJoUCReLQFa zNpDmgK/fxMg1n3n53dqek32zOpZHivnHRXTpGfip/a5LVlOhdJMxeKpkKwfuHNheFI8 Lvrg== X-Gm-Message-State: AOAM532PZFeZPTxRUVbCJmjt8J3/ZeHtrlBYPJjZQXhlMcWVNDD5gykm 2BgcfqZ1ZBuAKauNE425CKI= X-Google-Smtp-Source: ABdhPJz4tDG7dKUgK4ityFmg3vSOGhRLJ/zP52TGKw7ZCw4shjkEUgDQXycsjH6d4iUmEOJtvcTqfA== X-Received: by 2002:ac2:548b:: with SMTP id t11mr839549lfk.181.1607512965721; Wed, 09 Dec 2020 03:22:45 -0800 (PST) Received: from xi.terra (c-beaee455.07-184-6d6c6d4.bbcust.telenor.se. [85.228.174.190]) by smtp.gmail.com with ESMTPSA id y13sm139426lfg.189.2020.12.09.03.22.44 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 09 Dec 2020 03:22:44 -0800 (PST) Received: from johan by xi.terra with local (Exim 4.93.0.4) (envelope-from ) id 1kmxZ7-0003bm-8G; Wed, 09 Dec 2020 12:23:25 +0100 Date: Wed, 9 Dec 2020 12:23:25 +0100 From: Johan Hovold To: Steffen Trumtrar Cc: Greg Kroah-Hartman , Jiri Slaby , linux-serial@vger.kernel.org Subject: Re: [PATCH 1/2] tty: serial: 8250: always call tx_chars under spinlock Message-ID: References: <20201209091728.2357-1-s.trumtrar@pengutronix.de> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20201209091728.2357-1-s.trumtrar@pengutronix.de> Precedence: bulk List-ID: X-Mailing-List: linux-serial@vger.kernel.org On Wed, Dec 09, 2020 at 10:17:27AM +0100, Steffen Trumtrar wrote: > In most cases serial8250_tx_chars is called with spinlock held. > Fix the remaining location, too. Please explain where __start_tx() is called without holding the port lock and consider fixing that up. > Signed-off-by: Steffen Trumtrar > --- > drivers/tty/serial/8250/8250_port.c | 6 +++++- > 1 file changed, 5 insertions(+), 1 deletion(-) > > diff --git a/drivers/tty/serial/8250/8250_port.c b/drivers/tty/serial/8250/8250_port.c > index b0af13074cd3..3310c2b70138 100644 > --- a/drivers/tty/serial/8250/8250_port.c > +++ b/drivers/tty/serial/8250/8250_port.c > @@ -1559,6 +1559,7 @@ static void serial8250_stop_tx(struct uart_port *port) > static inline void __start_tx(struct uart_port *port) > { > struct uart_8250_port *up = up_to_u8250p(port); > + unsigned long flags; > > if (up->dma && !up->dma->tx_dma(up)) > return; > @@ -1569,8 +1570,11 @@ static inline void __start_tx(struct uart_port *port) > > lsr = serial_in(up, UART_LSR); > up->lsr_saved_flags |= lsr & LSR_SAVE_FLAGS; > - if (lsr & UART_LSR_THRE) > + if (lsr & UART_LSR_THRE) { > + spin_lock_irqsave(&port->lock, flags); > serial8250_tx_chars(up); > + spin_unlock_irqrestore(&port->lock, flags); > + } Since several callers of __start_tx() do hold the lock, this change will introduce a deadlock. > } > } Johan