Date: Wed, 7 Jan 2009 04:28:03 +0100
From: Nick Piggin <npiggin@suse.de>
To: Andi Kleen <andi@firstfloor.org>
Cc: Christoph Hellwig <hch@infradead.org>,
       Andrew Morton <akpm@linux-foundation.org>, linux-kernel@vger.kernel.org
Subject: Re: 2.6.29 -mm merge plans
Message-ID: <20090107032802.GA22559@wotan.suse.de>
References: <20090105004300.19ed52d1.akpm@linux-foundation.org> <20090106225744.GA10553@infradead.org> <20090106151131.b6c4ff0b.akpm@linux-foundation.org> <20090106232418.GB25103@infradead.org> <20090107011448.GB3390@wotan.suse.de> <87tz8b3nfe.fsf@basil.nowhere.org> <20090107014915.GE3390@wotan.suse.de> <20090107025725.GJ496@one.firstfloor.org>
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On Wed, Jan 07, 2009 at 03:57:25AM +0100, Andi Kleen wrote:
> > sys_sync B which is invoked *after* sys_sync caller A should not
> > return before A. If you didn't have a global lock, they'd tend to
> > block one another's pages anyway. I think it's OK.
> 
> It means that you cannot reboot because reboot does sync.
> What happens when the sync gets stuck somewhere on a really
> slow device?

I don't follow you.

The sync gets "stuck" because it is writing out dirty data. You
don't want to reboot before that happens, which is exactly the
reason why sync gets called (although it is probably not needed
anyway if all filesystems get unmounted).

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