Re: [Lsf10-pc] Current MM topics for LSF10/MM Summit 8-9 August in Boston

[Gleb Natapov <gleb@redhat.com>]

On Mon, Jun 21, 2010 at 03:16:08PM +0200, Andrea Arcangeli wrote:
> > KOSAKI Motohiro		get_user_pages vs COW problem
> 
> Just a side note, not sure exactly what is meant to be discussed about
> this bug, considering the fact this is still unsolved isn't technical
> problem as there were plenty of fixes available, and the one that seem
> to had better chance to get included was the worst one in my view, as
> it tried to fix it in a couple of gup caller (but failed, also because
> finding all put_page pin release is kind of a pain as they're spread
> all over the place and not identified as gup_put_page, and in addition
> to the instability and lack of completeness of the fix, it was also
> the most inefficient as it added unnecessary and coarse locking) plus
> all gup callers are affected, not just a few. I normally call it gup
> vs fork race. Luckily not all threaded apps uses O_DIRECT and fork and
> pretend to do the direct-io in different sub-page chunks of the same
> page from different threads (KVM would probably be affected if it
> didn't use MADV_DONTFORK on the O_DIRECT memory, as it might run fork
> to execute some network script when adding an hotplug pci net device
> for example). But surely we can discuss the fix we prefer for this
> bug, or at least we can agree it needs fixing.
> 
KVM is actually affected by the bug. The fix was posted today:
http://www.mail-archive.com/kvm@vger.kernel.org/msg36759.html

--
			Gleb.

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