From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-qc0-f170.google.com (mail-qc0-f170.google.com [209.85.216.170]) by kanga.kvack.org (Postfix) with ESMTP id 5C25B6B0032 for ; Thu, 7 May 2015 20:37:53 -0400 (EDT) Received: by qcbgu10 with SMTP id gu10so30075964qcb.2 for ; Thu, 07 May 2015 17:37:53 -0700 (PDT) Received: from relay4-d.mail.gandi.net (relay4-d.mail.gandi.net. [2001:4b98:c:538::196]) by mx.google.com with ESMTPS id w19si3793850qha.85.2015.05.07.17.37.52 for (version=TLSv1 cipher=RC4-SHA bits=128/128); Thu, 07 May 2015 17:37:52 -0700 (PDT) Date: Thu, 7 May 2015 17:37:48 -0700 From: josh@joshtriplett.org Subject: Re: [PATCH] devpts: If initialization failed, don't crash when opening /dev/ptmx Message-ID: <20150508003748.GA1033@cloud> References: <20150507003547.GA6862@jtriplet-mobl1> <20150507155919.16ab7177e4956d8f47803750@linux-foundation.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20150507155919.16ab7177e4956d8f47803750@linux-foundation.org> Sender: owner-linux-mm@kvack.org List-ID: To: Andrew Morton Cc: Linus Torvalds , Fengguang Wu , Iulia Manda , "Paul E. McKenney" , Fabian Frederick , Linux Memory Management List , linux-kernel@vger.kernel.org On Thu, May 07, 2015 at 03:59:19PM -0700, Andrew Morton wrote: > On Wed, 6 May 2015 17:35:47 -0700 Josh Triplett wrote: > > > If devpts failed to initialize, it would store an ERR_PTR in the global > > devpts_mnt. A subsequent open of /dev/ptmx would call devpts_new_index, > > which would dereference devpts_mnt and crash. > > > > Avoid storing invalid values in devpts_mnt; leave it NULL instead. > > Make both devpts_new_index and devpts_pty_new fail gracefully with > > ENODEV in that case, which then becomes the return value to the > > userspace open call on /dev/ptmx. > > It looks like the system is pretty crippled if init_devptr_fs() fails. > Can the user actually get access to consoles and do useful things in > this situation? Maybe it would be better to just give up and panic? Mounting devpts doesn't work without it, but you don't *need* to do that to run a viable system. A full-featured terminal might be unhappy. init=/bin/sh works, and a console login doesn't strictly require /dev/pts. A substantial initramfs or rescue system should work without /dev/pts mounted. I think this falls under Linus's comments elsewhere about BUG versus WARN. The system can continue and will function to some degree. panic() is more suitable for "if I even return from this function, horrible things will start happening". With this patch, all the functions provided by devpts gracefully fail if devpts did, so I don't see a good reason to panic(). > > @@ -676,12 +689,15 @@ static int __init init_devpts_fs(void) > > struct ctl_table_header *table; > > > > if (!err) { > > + static struct vfsmount *mnt; > > static is weird. I assume this was a braino? Copy/paste issue, yes. Fixed in v2. - Josh Triplett -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org