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=-2.3 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE, SPF_PASS,USER_AGENT_SANE_1 autolearn=no 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 DF970C3A5A9 for ; Wed, 4 Sep 2019 07:17:44 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id B1D3023402 for ; Wed, 4 Sep 2019 07:17:44 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1567581464; bh=O7gd31mCUn7hGnnq9Vb4w9PGZAT1XR/l+yS7ir1reAY=; h=Date:From:To:Cc:Subject:References:In-Reply-To:List-ID:From; b=ON/AAWRjDn1KEiEjL6DGVChdzq00CZEC/EpNPT/NTYk41Z8afz24k9ELqcdq0jkGQ xyfI6LI8LmN9Qm2Tduog8vzRR3W+dvUENbZFPnzVtPJixGxxMSfYBXR/GSGkI73dVj n7DMLgYJhERdeut7yN5azeetav4F5tJLhH5i/qOM= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729001AbfIDHRo (ORCPT ); Wed, 4 Sep 2019 03:17:44 -0400 Received: from mail.kernel.org ([198.145.29.99]:35628 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726033AbfIDHRn (ORCPT ); Wed, 4 Sep 2019 03:17:43 -0400 Received: from localhost (83-86-89-107.cable.dynamic.v4.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 F0DB32339D; Wed, 4 Sep 2019 07:17:41 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1567581462; bh=O7gd31mCUn7hGnnq9Vb4w9PGZAT1XR/l+yS7ir1reAY=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=NOhoz5G6GCo9WxNgbO+kAr9X58RxNU01X7KDOlCUdKrFrqKWCUaFCPbPw7tZM2iIn CPiyKY361fFEVx2mqCKpmYP678axzOBUqb92hV6f2hOh2VkrGTFYeGiuN0l6e2b0Ox uFLEMyB208cKexrDxkSbnJ4TrFkqYtEdFJxTLEns= Date: Wed, 4 Sep 2019 09:17:40 +0200 From: Greg Kroah-Hartman To: Martin =?iso-8859-1?Q?Hundeb=F8ll?= Cc: Jiri Slaby , Alan Cox , linux-kernel@vger.kernel.org, Sean =?iso-8859-1?Q?Nyekj=E6r?= , Esben Haabendal Subject: Re: [PATCH] tty: n_gsm: avoid recursive locking with async port hangup Message-ID: <20190904071740.GE18791@kroah.com> References: <20190822215601.9028-1-martin@geanix.com> <4fd2d737-14a8-6fe6-16a1-c5e6d924f9e6@geanix.com> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <4fd2d737-14a8-6fe6-16a1-c5e6d924f9e6@geanix.com> User-Agent: Mutt/1.12.1 (2019-06-15) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Aug 29, 2019 at 09:42:31PM +0200, Martin Hundebøll wrote: > On 22/08/2019 23.56, Martin Hundebøll wrote: > > When tearing down the n_gsm ldisc while one or more of its child ports > > are open, a lock dep warning occurs: > > > > [ 56.254258] ====================================================== > > [ 56.260447] WARNING: possible circular locking dependency detected > > [ 56.266641] 5.2.0-00118-g1fd58e20e5b0 #30 Not tainted > > [ 56.271701] ------------------------------------------------------ > > [ 56.277890] cmux/271 is trying to acquire lock: > > [ 56.282436] 8215283a (&tty->legacy_mutex){+.+.}, at: __tty_hangup.part.0+0x58/0x27c > > [ 56.290128] > > [ 56.290128] but task is already holding lock: > > [ 56.295970] e9e2b842 (&gsm->mutex){+.+.}, at: gsm_cleanup_mux+0x9c/0x15c > > [ 56.302699] > > [ 56.302699] which lock already depends on the new lock. > > [ 56.302699] > > [ 56.310884] > > [ 56.310884] the existing dependency chain (in reverse order) is: > > [ 56.318372] > > [ 56.318372] -> #2 (&gsm->mutex){+.+.}: > > [ 56.323624] mutex_lock_nested+0x1c/0x24 > > [ 56.328079] gsm_cleanup_mux+0x9c/0x15c > > [ 56.332448] gsmld_ioctl+0x418/0x4e8 > > [ 56.336554] tty_ioctl+0x96c/0xcb0 > > [ 56.340492] do_vfs_ioctl+0x41c/0xa5c > > [ 56.344685] ksys_ioctl+0x34/0x60 > > [ 56.348535] ret_fast_syscall+0x0/0x28 > > [ 56.352815] 0xbe97cc04 > > [ 56.355791] > > [ 56.355791] -> #1 (&tty->ldisc_sem){++++}: > > [ 56.361388] tty_ldisc_lock+0x50/0x74 > > [ 56.365581] tty_init_dev+0x88/0x1c4 > > [ 56.369687] tty_open+0x1c8/0x430 > > [ 56.373536] chrdev_open+0xa8/0x19c > > [ 56.377560] do_dentry_open+0x118/0x3c4 > > [ 56.381928] path_openat+0x2fc/0x1190 > > [ 56.386123] do_filp_open+0x68/0xd4 > > [ 56.390146] do_sys_open+0x164/0x220 > > [ 56.394257] kernel_init_freeable+0x328/0x3e4 > > [ 56.399146] kernel_init+0x8/0x110 > > [ 56.403078] ret_from_fork+0x14/0x20 > > [ 56.407183] 0x0 > > [ 56.409548] > > [ 56.409548] -> #0 (&tty->legacy_mutex){+.+.}: > > [ 56.415402] __mutex_lock+0x64/0x90c > > [ 56.419508] mutex_lock_nested+0x1c/0x24 > > [ 56.423961] __tty_hangup.part.0+0x58/0x27c > > [ 56.428676] gsm_cleanup_mux+0xe8/0x15c > > [ 56.433043] gsmld_close+0x48/0x90 > > [ 56.436979] tty_ldisc_kill+0x2c/0x6c > > [ 56.441173] tty_ldisc_release+0x88/0x194 > > [ 56.445715] tty_release_struct+0x14/0x44 > > [ 56.450254] tty_release+0x36c/0x43c > > [ 56.454365] __fput+0x94/0x1e8 > > > > Avoid the warning by doing the port hangup asynchronously. > > Any comments? Sorry, was waiting to see if anyone would review this, I'll go do it later today...