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=-10.1 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI, SIGNED_OFF_BY,SPF_PASS,URIBL_BLOCKED,USER_AGENT_GIT 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 1E540C41518 for ; Thu, 24 Jan 2019 19:44:10 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id DDB45218F0 for ; Thu, 24 Jan 2019 19:44:09 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1548359049; bh=tzSxricLIu1w/cd4mlrkb+yFGj6B+Zeo7fuR7WEfjAg=; h=From:To:Cc:Subject:Date:In-Reply-To:References:List-ID:From; b=TWUXU0tzYZnb9iyBQMKxrWtouTABs9nZQ0z+p1P/ysNvdmsMJ6RyUi16GX33e4UzV Im6KwvxP7wqYgmS7vZtgFQ3cVBSIc1MecjRBTlR7Jz2Vjd4rVw0YeexUZNt/jtT8s/ VCf/zy4/ZxNvqR5qOlJFXh8GKrFzERCTWr3CaiPs= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2387514AbfAXToI (ORCPT ); Thu, 24 Jan 2019 14:44:08 -0500 Received: from mail.kernel.org ([198.145.29.99]:44866 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1733294AbfAXToI (ORCPT ); Thu, 24 Jan 2019 14:44:08 -0500 Received: from localhost (5356596B.cm-6-7b.dynamic.ziggo.nl [83.86.89.107]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id BA612218D9; Thu, 24 Jan 2019 19:44:06 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1548359047; bh=tzSxricLIu1w/cd4mlrkb+yFGj6B+Zeo7fuR7WEfjAg=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=yBYihuOCLp/4gymk0AuwWpQDoJ7cmKmTb0jPYAdtnhcss7CgZQD7eUVA+nt/YEL/Y Xp6V1DsEKmFFKPM63vw0Wx+uUOBkaevLRUrGIWuQm2M9SU4Ty7GiQxgXvPB6B3ySqP UFTedNvuQY6dCrQxlxVggxpvrWORHltuQDzi88+E= From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, Sergey Senozhatsky , Petr Mladek , "Peter Zijlstra (Intel)" , Jiri Slaby , Andrew Morton , Waiman Long , Dmitry Safonov , Steven Rostedt , Sasha Levin Subject: [PATCH 4.20 081/127] tty/serial: do not free trasnmit buffer page under port lock Date: Thu, 24 Jan 2019 20:20:27 +0100 Message-Id: <20190124190215.561583313@linuxfoundation.org> X-Mailer: git-send-email 2.20.1 In-Reply-To: <20190124190211.984305387@linuxfoundation.org> References: <20190124190211.984305387@linuxfoundation.org> User-Agent: quilt/0.65 X-stable: review X-Patchwork-Hint: ignore MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Sender: stable-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: stable@vger.kernel.org 4.20-stable review patch. If anyone has any objections, please let me know. ------------------ [ Upstream commit d72402145ace0697a6a9e8e75a3de5bf3375f78d ] LKP has hit yet another circular locking dependency between uart console drivers and debugobjects [1]: CPU0 CPU1 rhltable_init() __init_work() debug_object_init uart_shutdown() /* db->lock */ /* uart_port->lock */ debug_print_object() free_page() printk() call_console_drivers() debug_check_no_obj_freed() /* uart_port->lock */ /* db->lock */ debug_print_object() So there are two dependency chains: uart_port->lock -> db->lock And db->lock -> uart_port->lock This particular circular locking dependency can be addressed in several ways: a) One way would be to move debug_print_object() out of db->lock scope and, thus, break the db->lock -> uart_port->lock chain. b) Another one would be to free() transmit buffer page out of db->lock in UART code; which is what this patch does. It makes sense to apply a) and b) independently: there are too many things going on behind free(), none of which depend on uart_port->lock. The patch fixes transmit buffer page free() in uart_shutdown() and, additionally, in uart_port_startup() (as was suggested by Dmitry Safonov). [1] https://lore.kernel.org/lkml/20181211091154.GL23332@shao2-debian/T/#u Signed-off-by: Sergey Senozhatsky Reviewed-by: Petr Mladek Acked-by: Peter Zijlstra (Intel) Cc: Greg Kroah-Hartman Cc: Jiri Slaby Cc: Andrew Morton Cc: Waiman Long Cc: Dmitry Safonov Cc: Steven Rostedt Signed-off-by: Greg Kroah-Hartman Signed-off-by: Sasha Levin --- drivers/tty/serial/serial_core.c | 22 ++++++++++++++++------ 1 file changed, 16 insertions(+), 6 deletions(-) diff --git a/drivers/tty/serial/serial_core.c b/drivers/tty/serial/serial_core.c index c439a5a1e6c0..d4cca5bdaf1c 100644 --- a/drivers/tty/serial/serial_core.c +++ b/drivers/tty/serial/serial_core.c @@ -205,10 +205,15 @@ static int uart_port_startup(struct tty_struct *tty, struct uart_state *state, if (!state->xmit.buf) { state->xmit.buf = (unsigned char *) page; uart_circ_clear(&state->xmit); + uart_port_unlock(uport, flags); } else { + uart_port_unlock(uport, flags); + /* + * Do not free() the page under the port lock, see + * uart_shutdown(). + */ free_page(page); } - uart_port_unlock(uport, flags); retval = uport->ops->startup(uport); if (retval == 0) { @@ -268,6 +273,7 @@ static void uart_shutdown(struct tty_struct *tty, struct uart_state *state) struct uart_port *uport = uart_port_check(state); struct tty_port *port = &state->port; unsigned long flags = 0; + char *xmit_buf = NULL; /* * Set the TTY IO error marker @@ -298,14 +304,18 @@ static void uart_shutdown(struct tty_struct *tty, struct uart_state *state) tty_port_set_suspended(port, 0); /* - * Free the transmit buffer page. + * Do not free() the transmit buffer page under the port lock since + * this can create various circular locking scenarios. For instance, + * console driver may need to allocate/free a debug object, which + * can endup in printk() recursion. */ uart_port_lock(state, flags); - if (state->xmit.buf) { - free_page((unsigned long)state->xmit.buf); - state->xmit.buf = NULL; - } + xmit_buf = state->xmit.buf; + state->xmit.buf = NULL; uart_port_unlock(uport, flags); + + if (xmit_buf) + free_page((unsigned long)xmit_buf); } /** -- 2.19.1