From patchwork Wed Sep 30 12:04:32 2020 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Will Deacon X-Patchwork-Id: 287347 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=-13.6 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED, DKIM_VALID, DKIM_VALID_AU, INCLUDES_PATCH, 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 55C81C4727E for ; Wed, 30 Sep 2020 12:04:43 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 1CDB620789 for ; Wed, 30 Sep 2020 12:04:43 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1601467483; bh=GykIBSaiDmEJ3XNEf9HGHAkoXZDo5xF4J1k3EoMvwoQ=; h=From:To:Cc:Subject:Date:List-ID:From; b=N/Y3U+eN1ndXgM3HHxE+4YGU5cPO6TklWnZwPWzEkqpQOeTdRnSMQdNIENqw9vX1v 0wyNRhR7DugSWLl2WQL99AFLttBYwzLyFMZMKkTzGgwgYOw91Nr1r3kR/J0wC49isz O/oUcuP+L0EV5I9Ir4teNqVs3C81dmulwIIYnO7g= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729247AbgI3MEj (ORCPT ); Wed, 30 Sep 2020 08:04:39 -0400 Received: from mail.kernel.org ([198.145.29.99]:59174 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728270AbgI3MEj (ORCPT ); Wed, 30 Sep 2020 08:04:39 -0400 Received: from localhost.localdomain (236.31.169.217.in-addr.arpa [217.169.31.236]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id 4218C2076B; Wed, 30 Sep 2020 12:04:37 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1601467478; bh=GykIBSaiDmEJ3XNEf9HGHAkoXZDo5xF4J1k3EoMvwoQ=; h=From:To:Cc:Subject:Date:From; b=f99KUqvqfomYjYMNPm/3zHNXcASLOTXscOvNPPIepLguIQ9EHBo0TzXHorvKVdW8b QnkTrmvJoFqz2kBpm/RZr9+GXmKYNQ6aytmUsTT88cUsNDZlkW6Et5y9Q/+6ghXzHM YrAcx89aIlNjuUc4MshU5oVeSU+CL2El+eM9NEk8= From: Will Deacon To: linux-serial@vger.kernel.org Cc: linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org, Peter Zijlstra , stable@vger.kernel.org, Russell King , Greg Kroah-Hartman , Jiri Slaby , Will Deacon Subject: [PATCH] serial: pl011: Fix lockdep splat when handling magic-sysrq interrupt Date: Wed, 30 Sep 2020 13:04:32 +0100 Message-Id: <20200930120432.16551-1-will@kernel.org> X-Mailer: git-send-email 2.20.1 MIME-Version: 1.0 Precedence: bulk List-ID: X-Mailing-List: linux-serial@vger.kernel.org From: Peter Zijlstra 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 --- drivers/tty/serial/amba-pl011.c | 11 +++++++---- 1 file changed, 7 insertions(+), 4 deletions(-) diff --git a/drivers/tty/serial/amba-pl011.c b/drivers/tty/serial/amba-pl011.c index 67498594d7d7..87dc3fc15694 100644 --- 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, const struct uart_amba_port *uap, */ 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_amba_port *uap) 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;