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

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Message-Id: <E1MDuEI-0006BC-1C@pomaz-ex.szeredi.hu>
Date:	Tue, 09 Jun 2009 07:50:38 +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 06:44:41PM +0200, Miklos Szeredi wrote:
> 
> > 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".
> 
> Welcome to reality...
> 
> * bread() is non-interruptible
> * so's copy_from_user()/copy_to_user()

And why should revoke(2) care?  Just wait for the damn thing to
finish.  Why exactly do these need to be interruptible?

Okay, if we want revoke or umount -f to be instantaneous then all that
needs to be taken care of.  But does it *need* to be?

My idea of revoke is something like below:

  - make sure no new operations are started on the file
  - check state of tasks for ongoing operations, if interruptible send signal
  - wait for all pending operations to finish
  - kill file

Thanks,
Miklos
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