linux-kernel - Re: [GIT PULL] please pull ummunotify

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Message-Id: <20090911151930.DB6B.A69D9226@jp.fujitsu.com>
Date:	Fri, 11 Sep 2009 15:21:35 +0900 (JST)
From:	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
To:	Brice Goglin <Brice.Goglin@...ia.fr>
Cc:	kosaki.motohiro@...fujitsu.com, Roland Dreier <rdreier@...co.com>,
	torvalds@...ux-foundation.org, akpm@...ux-foundation.org,
	jsquyres@...co.com, linux-rdma@...r.kernel.org,
	general@...ts.openfabrics.org, linux-kernel@...r.kernel.org
Subject: Re: [GIT PULL] please pull ummunotify

> Roland Dreier wrote:
> >  > Can I this version already solved fork() + COW issue? if so, could you
> >  > please explain what happen at fork. Obviously RDMA point to either parent
> >  > or child page, not both. but Corrent COW rule is, first touch process
> >  > get copyed page and other process still own original page. I think it's 
> >  > unpecected behavior form RDMA.
> >
> > No, ummunotify doesn't really help that much with fork() + COW.  If a
> > parent forks and then touches pages that are actively in use for RDMA,
> > then of course they get COWed and RDMA goes to the wrong memory (from
> > the point of view of the parent).
> >   
> 
> My understanding of the code is that fork will end-up calling
> copy_page_range() on all VMA, and copy_page_range() calls
> mmu_notifier_invalidate_range_start() if  is_cow_mapping() is true,
> which should be the case here. So you should get some invalidate events
> on fork.

Worried...
Anybody haven't test fork() case yet???



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