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

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Date:	Mon, 8 Jun 2009 18:50:18 +0100
From:	Al Viro <viro@...IV.linux.org.uk>
To:	Miklos Szeredi <miklos@...redi.hu>
Cc:	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, 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()
* IO we are stuck upon _might_ be interruptible, but by sending a signal
to some other process

... just for starters.  If you sign up for auditing the tree to eliminate
"something's stuck in D state", you are welcome to it.  Mind you, you'll
have to audit filesystems for "doesn't check if metadata IO has failed"
first, but that _really_ needs to be done anyway.  On the ongoing basis.

Drivers, of course, are even more interesting - looking through foo_ioctl()
instances is a wonderful way to lower pH in stomach, but that's on the
"we want revoke()" side of it.
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