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

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Message-ID: <4970B0F2.6040507@redhat.com>
Date:	Fri, 16 Jan 2009 10:08:18 -0600
From:	Eric Sandeen <sandeen@...hat.com>
To:	Theodore Tso <tytso@....edu>, Valdis.Kletnieks@...edu,
	Pavel Machek <pavel@...e.cz>,
	Eric Sandeen <sandeen@...hat.com>,
	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

Theodore Tso wrote:
> On Fri, Jan 16, 2009 at 10:17:09AM -0500, 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...
> 
> My biggest complaint is that the two operations are largely
> orthogonal.  Emergency sync and unfreeze are two very different
> operations, and while emergency sync is largely harmless, it just
> seems really unclean to combine the two.  For one thing, it'll be
> extremely non-obvious that emergency sync implies unfreeze, and
> changing the sysrq help to say emergency-Sync-and-unfreeze just
> screams "kludge"....
> 
> 						- Ted

Yeah, they really are orthogonal, it's true.  Ok, if people are willing
to give up 'z' I'll move it there.

-Eric
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