linux-kernel - Re: [RFC][PATCH 4/5] must hold lock_super() to set initial mount writer

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Message-Id: <1209659204.4461.65.camel@nimitz.home.sr71.net>
Date:	Thu, 01 May 2008 09:26:44 -0700
From:	Dave Hansen <dave@...ux.vnet.ibm.com>
To:	Miklos Szeredi <miklos@...redi.hu>
Cc:	linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org,
	viro@...iv.linux.org.uk, hch@...radead.org,
	trond.myklebust@....uio.no
Subject: Re: [RFC][PATCH 4/5] must hold lock_super() to set initial mount
	writer

On Wed, 2008-04-30 at 11:25 +0200, Miklos Szeredi wrote:
> > We need lock_mnt_writers() during a remount in order
> > to keep mnt->__mnt_writers from changing so that we
> > get a consistent look at if a sb currently has anyone
> > writing to it.
> > 
> > But, we need to lock writers out for an extended
> > period, even during the ->remount_fs() operation.
> > That's because we do conclusively make the fs
> > r/o until *after* the ->remount_fs().
> 
> So?  Why don't we mark the fs r/o _before_ calling ->remount_fs() and
> if that fails, just mark it r/w again.
> 
> OK, we'll deny writes in that interval, but I don't see that as a big
> problem.  And it would simplify the implementation considerably.

Personally, I think that's a bit messy.  People might start getting
-EROFS when they never, ever *HAD* a r/o FS.  They may have made a
request for one, but they never actually hard one.

I also understand what you're saying.  If we were able to loosen up some
of the requirements it would certainly make the patches simpler.  How
does everyone else feel about this?

-- Dave

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