linux-kernel - Re: [PATCH] Allow SysRq emergency sync to thaw frozen filesystems

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Message-Id: <E1LOBlz-0001tI-Oo@be1.7eggert.dyndns.org>
Date:	Sat, 17 Jan 2009 15:03:39 +0100
From:	Bodo Eggert <7eggert@....de>
To:	Eric Sandeen <sandeen@...deen.net>, Valdis.Kletnieks@...edu,
	Eric Sandeen <sandeen@...hat.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
	t-sato@...jp.nec.com
Subject: Re: [PATCH] Allow SysRq emergency sync to thaw frozen filesystems

Eric Sandeen <sandeen@...deen.net> wrote:
> Valdis.Kletnieks@...edu wrote:
>> On Thu, 15 Jan 2009 21:59:10 CST, Eric Sandeen said:

>>> Oh, actually, I'd think not.  If the freeze was done properly by the
>>> filesystem, all data was flushed, the fs was quiesced, and new IO was
>>> blocked.  pdflush should never be visiting these...
>> 
>> Yes, but a lot of 'if's - and usually you're reaching for sysrq-S precisely
>> *because* you suspect that stuff wasn't happening properly on its own...
> 
> Actually, only one if - if the fs implemented freeze properly.
> 
> Well, the use case I envision here is something like:
> 
> # freeze /my/mount/point/to/fs/to/snapshot
> 
> except oops, that wasn't mounted, and you just froze your root fs.

Maybe freeze should protect against that by requiring to specify the exact
mountpount, unless you say freeze --subdir?

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