linux-kernel - Re: [PATCH] Syscalls: reboot: Add options to the reboot syscall to remount filesystems ro

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Date:	Thu, 3 Mar 2011 18:55:11 -0800
From:	Scott James Remnant <scott@...split.com>
To:	Mark Lord <kernel@...savvy.com>
Cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	Ken Sumrall <ksumrall@...roid.com>,
	linux-kernel@...r.kernel.org,
	Alexander Viro <viro@...iv.linux.org.uk>,
	Christoph Hellwig <hch@....de>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Jan Kara <jack@...e.cz>, Jens Axboe <axboe@...nel.dk>,
	Matthew Wilcox <matthew@....cx>,
	Eric Paris <eparis@...hat.com>,
	Dave Young <hidave.darkstar@...il.com>,
	Jiri Slaby <jslaby@...e.cz>, James Morris <jmorris@...ei.org>,
	linux-fsdevel@...r.kernel.org
Subject: Re: [PATCH] Syscalls: reboot: Add options to the reboot syscall to
 remount filesystems ro

On Thu, Mar 3, 2011 at 6:48 PM, Mark Lord <kernel@...savvy.com> wrote:
> On 11-03-03 09:33 PM, Linus Torvalds wrote:
>> On Thu, Mar 3, 2011 at 6:00 PM, Ken Sumrall <ksumrall@...roid.com> wrote:
>>>
>>> Writing a single byte to /proc/sysrq-trigger is an asynchronous
>>> operation, with no obvious way to be informed that it has completed
>>> the remount.
>>
>> Right you are. That's something of a misfeature, but it comes from the
>> way sysrq works: obviously the "real" sysrq thing is about keyboard
>> input, so all the sysrq stuff has to be async.
>>
>> The fact that that async nature then ends up also affecting the
>> /proc/sysrq-trigger case (which _could_ be synchronous) is a bit sad
>> in this case.
>
> Agreed.
>
> I have the echo s/u to sysrq-trigger (plus a 2-sec sleep ala MS-Win)
> on my Ubuntu systems here, because their shutdown "sequence"
> is racy and buggy, and frequently powers off the box with the
> rootfs still mounted rw otherwise.
>
> And don't get me started about the races on system startup
>  -- "upstart" is an abomination, or at least the Ubuntu use of it is.
>
Ubuntu doesn't use Upstart on shutdown, it uses the plain-old sysv init scripts.

Oddly enough I don't see any bugs filed by you about startup issues?
Now, don't get me wrong, I'm not saying Ubuntu is perfect here - but
I'm not aware of any races that are Upstart's fault. If there are,
please file bugs! How else am I to fix them if I don't know about
them?

Scott
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