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

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Message-ID: <20090608185041.GN8633@ZenIV.linux.org.uk>
Date:	Mon, 8 Jun 2009 19:50:41 +0100
From:	Al Viro <viro@...IV.linux.org.uk>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	Miklos Szeredi <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,
	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 11:01:51AM -0700, Linus Torvalds wrote:
> 
> 
> On Mon, 8 Jun 2009, Al Viro wrote:
> > 
> > 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
> 
> We can probably improve on these, though.
> 
> Like the copy_to/from_user thing. We might well be able to do that whole 
> "if it's a fatal signal, return early" thing.
> 
> So in the _general_ case - no, we probably can't fix things. But we could 
> likely at least improve in some common cases if we cared.

Sure, even though I'm not at all certain that copy_from_user() is that easy.
We can make locking current->mm in there interruptible, all right, but that's
only a part of the answer - even aside of the allocations, we'd need vma
->fault() interruptible as well, which leads to interruptible instances of
->readpage(), with all the fun _that_ would be.
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