linux-kernel - Re: [PATCH 0/23] File descriptor hot-unplug support v2

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Message-Id: <E1MDhxh-0004nz-Qm@pomaz-ex.szeredi.hu>
Date:	Mon, 08 Jun 2009 18:44:41 +0200
From:	Miklos Szeredi <miklos@...redi.hu>
To:	viro@...IV.linux.org.uk
CC:	miklos@...redi.hu, ebiederm@...ssion.com,
	linux-kernel@...r.kernel.org, linux-pci@...r.kernel.org,
	linux-mm@...ck.org, linux-fsdevel@...r.kernel.org,
	hugh@...itas.com, tj@...nel.org, adobriyan@...il.com,
	torvalds@...ux-foundation.org, alan@...rguk.ukuu.org.uk,
	gregkh@...e.de, npiggin@...e.de, akpm@...ux-foundation.org,
	hch@...radead.org
Subject: Re: [PATCH 0/23] File descriptor hot-unplug support v2

On Mon, 8 Jun 2009, Al Viro wrote:
> On Mon, Jun 08, 2009 at 11:41:19AM +0200, Miklos Szeredi wrote:
> > On Sat, 6 Jun 2009, Al Viro wrote:
> > > Frankly, I very much suspect that force-umount is another case like that;
> > > we'll need a *lot* of interesting cooperation from fs for that to work and
> > > to be useful.  I'd be delighted to be proven incorrect on that one, so
> > > if you have anything serious in that direction, please share the details.
> > 
> > Umm, not sure why we'd need cooperation from the fs.  Simply wait for
> > the operation to exit the filesystem or driver.  If it's a blocking
> > operation, send a signal to interrupt it.
> 
> And making sure that operations *are* interruptible (and that we can cope
> with $BIGNUM new failure exits correctly) does not qualify as cooperation?

I'm still not getting what the problem is.  AFAICS file operations are
either

 a) non-interruptible but finish within a short time or
 b) may block indefinitely but are interruptible (or at least killable).

Anything else is already problematic, resulting in processes "stuck in
D state".

Can you give a more concrete example about your worries?

Thanks,
Miklos
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