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=-9.8 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI, SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,USER_AGENT_GIT autolearn=unavailable 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 860F0C388F7 for ; Sat, 31 Oct 2020 11:45:54 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 46C4B20739 for ; Sat, 31 Oct 2020 11:45:54 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1604144754; bh=jIHPrIt3PDmeivFwBtgkZ3njTlUGFDZiU2DvIsHM8QY=; h=From:To:Cc:Subject:Date:In-Reply-To:References:List-ID:From; b=lXnJzMR2JPlqY3+DWw+CneB68mmcUcDbdBxKElmDlySkkG9M/4rZOW2LaAhpjsKmg HmLrl1a6+essgvhLPhZ4/w9y3kT2eAZGfdx1vTGpY+VY21+y9+hNKZXTdDehsgNGCW JsEAwTKcL3YiEKczHxKT0i3sIvuXKZYst1Xg5YZE= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728312AbgJaLpx (ORCPT ); Sat, 31 Oct 2020 07:45:53 -0400 Received: from mail.kernel.org ([198.145.29.99]:46934 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728304AbgJaLpu (ORCPT ); Sat, 31 Oct 2020 07:45:50 -0400 Received: from localhost (83-86-74-64.cable.dynamic.v4.ziggo.nl [83.86.74.64]) (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 0E01D2074F; Sat, 31 Oct 2020 11:45:48 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1604144749; bh=jIHPrIt3PDmeivFwBtgkZ3njTlUGFDZiU2DvIsHM8QY=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=nJ7ubclHl6wez0oRx5ShN6Vr1nPebO/LLzkC4IxEFKlEMhul8Gzg7qOim02NXny1l y+zBEBODo6nNjr8EhqkaDdRsOgmELTdfv9LgNDWp+L147asDtyO9JCOYuyXkhhb5GA sQARqzseuzDf16cNW6uTMRnJBmaoBg15P3pRO2aQ= From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, Russell King , Jiri Slaby , Peter Zijlstra , Will Deacon Subject: [PATCH 5.9 67/74] serial: pl011: Fix lockdep splat when handling magic-sysrq interrupt Date: Sat, 31 Oct 2020 12:36:49 +0100 Message-Id: <20201031113503.239191808@linuxfoundation.org> X-Mailer: git-send-email 2.29.2 In-Reply-To: <20201031113500.031279088@linuxfoundation.org> References: <20201031113500.031279088@linuxfoundation.org> User-Agent: quilt/0.66 MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Peter Zijlstra commit 534cf755d9df99e214ddbe26b91cd4d81d2603e2 upstream. Issuing a magic-sysrq via the PL011 causes the following lockdep splat, which is easily reproducible under QEMU: | sysrq: Changing Loglevel | sysrq: Loglevel set to 9 | | ====================================================== | WARNING: possible circular locking dependency detected | 5.9.0-rc7 #1 Not tainted | ------------------------------------------------------ | systemd-journal/138 is trying to acquire lock: | ffffab133ad950c0 (console_owner){-.-.}-{0:0}, at: console_lock_spinning_enable+0x34/0x70 | | but task is already holding lock: | ffff0001fd47b098 (&port_lock_key){-.-.}-{2:2}, at: pl011_int+0x40/0x488 | | which lock already depends on the new lock. [...] | Possible unsafe locking scenario: | | CPU0 CPU1 | ---- ---- | lock(&port_lock_key); | lock(console_owner); | lock(&port_lock_key); | lock(console_owner); | | *** DEADLOCK *** The issue being that CPU0 takes 'port_lock' on the irq path in pl011_int() before taking 'console_owner' on the printk() path, whereas CPU1 takes the two locks in the opposite order on the printk() path due to setting the "console_owner" prior to calling into into the actual console driver. Fix this in the same way as the msm-serial driver by dropping 'port_lock' before handling the sysrq. Cc: # 4.19+ Cc: Russell King Cc: Greg Kroah-Hartman Cc: Jiri Slaby Link: https://lore.kernel.org/r/20200811101313.GA6970@willie-the-truck Signed-off-by: Peter Zijlstra Tested-by: Will Deacon Signed-off-by: Will Deacon Link: https://lore.kernel.org/r/20200930120432.16551-1-will@kernel.org Signed-off-by: Greg Kroah-Hartman --- drivers/tty/serial/amba-pl011.c | 11 +++++++---- 1 file changed, 7 insertions(+), 4 deletions(-) --- a/drivers/tty/serial/amba-pl011.c +++ b/drivers/tty/serial/amba-pl011.c @@ -308,8 +308,9 @@ static void pl011_write(unsigned int val */ static int pl011_fifo_to_tty(struct uart_amba_port *uap) { - u16 status; unsigned int ch, flag, fifotaken; + int sysrq; + u16 status; for (fifotaken = 0; fifotaken != 256; fifotaken++) { status = pl011_read(uap, REG_FR); @@ -344,10 +345,12 @@ static int pl011_fifo_to_tty(struct uart flag = TTY_FRAME; } - if (uart_handle_sysrq_char(&uap->port, ch & 255)) - continue; + spin_unlock(&uap->port.lock); + sysrq = uart_handle_sysrq_char(&uap->port, ch & 255); + spin_lock(&uap->port.lock); - uart_insert_char(&uap->port, ch, UART011_DR_OE, ch, flag); + if (!sysrq) + uart_insert_char(&uap->port, ch, UART011_DR_OE, ch, flag); } return fifotaken;