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

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Date:	Tue, 9 Jun 2009 12:52:51 +0200
From:	Nick Piggin <npiggin@...e.de>
To:	"Eric W. Biederman" <ebiederm@...ssion.com>
Cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	Al Viro <viro@...IV.linux.org.uk>,
	Miklos Szeredi <miklos@...redi.hu>,
	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,
	akpm@...ux-foundation.org, hch@...radead.org
Subject: Re: [PATCH 0/23] File descriptor hot-unplug support v2

On Mon, Jun 08, 2009 at 11:42:53PM -0700, Eric W. Biederman wrote:
> Linus Torvalds <torvalds@...ux-foundation.org> writes:
> 
> > On Mon, 8 Jun 2009, Al Viro wrote:
> >> 
> >> 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.
> >
> > We already have all that - the NFS people wanted it.
> >
> > More importantly, you don't actually need to interrupt readpage itself - 
> > you just need to stop _waiting_ on it. So in your fault handler, just stop 
> > waiting, and instead just return FAULT_RETRY or whatever.
> 
> That sounds doable.  Has that code been merged yet?
> 
> I took a quick look and it didn't see anyone breaking out of page fault with a
> signal or code to really handle that.

The problem is get_user_pages I think. Now that we have a good number of
fault flags, we can pass down whether the caller is able to be
interrupted or not.

Ben H had some interest in doing this, but I don't know how far he got
with it.

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