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=-13.5 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,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 CD72EC4727E for ; Wed, 30 Sep 2020 12:06:37 +0000 (UTC) Received: from merlin.infradead.org (merlin.infradead.org [205.233.59.134]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id 668362076B for ; Wed, 30 Sep 2020 12:06:37 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=lists.infradead.org header.i=@lists.infradead.org header.b="logFSq7G"; dkim=fail reason="signature verification failed" (1024-bit key) header.d=kernel.org header.i=@kernel.org header.b="f99KUqvq" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 668362076B Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=kernel.org Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=merlin.20170209; h=Sender:Content-Transfer-Encoding: Content-Type:Cc:List-Subscribe:List-Help:List-Post:List-Archive: List-Unsubscribe:List-Id:MIME-Version:Message-Id:Date:Subject:To:From: Reply-To:Content-ID:Content-Description:Resent-Date:Resent-From:Resent-Sender :Resent-To:Resent-Cc:Resent-Message-ID:In-Reply-To:References:List-Owner; bh=2ww/TlSEbMleJM3VMMeQsdRVP/djluUPM1vgGncP7oI=; b=logFSq7GSnINOQgMOiO5Jz+a5E wnyC6dsJxjFuxsVNqSYlCFvjytcd+E69Lz6daLDj6/PQohOcNpaJ+Z5OCfux5gDf51lJ6rAdCyoyY jA/bTsFnHsqtXhPv7JCA8DqZAKyg8RxGy8xyQ9fUm5onMkm2BQXO0kqk+3+vzoaErfiVgz+pCriJ2 T4zyDroJmzD5Ei/GzdrmAmAWLeNMGBYUJ9odJVQAPxJy6TbcgYvfxPukYb9b3tpC9C1j7yPV4opI0 //Zjgn5mJAPygA+FFtglWt5mpXlM/8IlUSKIuSkUc4mcsw4v36jnK1/CE40T8loMvX1MTtDDb2awq ujmjXbaA==; Received: from localhost ([::1] helo=merlin.infradead.org) by merlin.infradead.org with esmtp (Exim 4.92.3 #3 (Red Hat Linux)) id 1kNaqf-0008PJ-U1; Wed, 30 Sep 2020 12:04:41 +0000 Received: from mail.kernel.org ([198.145.29.99]) by merlin.infradead.org with esmtps (Exim 4.92.3 #3 (Red Hat Linux)) id 1kNaqd-0008OJ-LX for linux-arm-kernel@lists.infradead.org; Wed, 30 Sep 2020 12:04:40 +0000 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 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 X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20200930_080439_852982_0318D1D8 X-CRM114-Status: GOOD ( 17.83 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Will Deacon , Peter Zijlstra , Greg Kroah-Hartman , linux-kernel@vger.kernel.org, stable@vger.kernel.org, Russell King , Jiri Slaby , linux-arm-kernel@lists.infradead.org Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.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; -- 2.28.0.709.gb0816b6eb0-goog _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel