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

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Message-ID: <4970A78B.8050605@redhat.com>
Date:	Fri, 16 Jan 2009 09:28:11 -0600
From:	Eric Sandeen <sandeen@...hat.com>
To:	Valdis.Kletnieks@...edu
CC:	Pavel Machek <pavel@...e.cz>,
	linux-fsdevel <linux-fsdevel@...r.kernel.org>,
	linux-kernel Mailing List <linux-kernel@...r.kernel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Takashi Sato <t-sato@...jp.nec.com>
Subject: Re: [PATCH] Allow SysRq emergency sync to thaw frozen filesystems

Valdis.Kletnieks@...edu wrote:
> On Fri, 16 Jan 2009 09:48:28 +0100, Pavel Machek said:
> 
>> Emergency Sync should not do this. Invent another key.
>>
>> ...because otherwise, if you hit emergency sync but the system is
>> still alive and relies on filesystem freezing, bad stuff will happen.
> 
> Under what conditions would a system be alive and relying on freezing,
> *and* an emergency thaw would be worse than whatever reason you're doing
> an emergency sync?
> 
> Hmm.. guess you *could* get into trouble if you tried to do a Sysrq-[not-s]
> and hit the wrong key - but you have the same danger if you have *any*
> sysrq- invoking an emergency_thaw and hit it by accident...

I could certainly use up another key ('z' is available for unfreeZe) but
I have the same question; under what conditions do you expect to need an
emergency sync and also need to maintain frozen filesystems as frozen?

>From a maximum flexibility and control perspective, it'd be better to
have them separated I suppose.  Is it worth using up another available key?

-Eric

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