linux-kernel - Re: [patch 1/5] vmalloc: do not check for freed locks on user maps

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Date:	Thu, 6 Mar 2008 09:56:43 +1100
From:	Nick Piggin <nickpiggin@...oo.com.au>
To:	Thomas Gleixner <tglx@...utronix.de>
Cc:	LKML <linux-kernel@...r.kernel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Greg KH <greg@...ah.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Ingo Molnar <mingo@...e.hu>
Subject: Re: [patch 1/5] vmalloc: do not check for freed locks on user maps

On Thursday 06 March 2008 04:20, Thomas Gleixner wrote:
> On Thu, 6 Mar 2008, Nick Piggin wrote:
> > On Thursday 06 March 2008 03:03, Thomas Gleixner wrote:
> > > User maps do not contain kernel internal objects. No need to check
> > > them.
> >
> > Why not? Depends on your definition of kernel internal... and
> > objects ;)
> >
> > Drivers could create and manage some objects in this vmalloc
> > area. They are no longer internal if you map them to userspace,
> > but I still don't think you want to vunmap it until those
> > object lifetimes are finished.
>
> Well, in case of the locks I have a hard time to figure out how you
> use a spinlock/mutex with a user space address. The same applies for
> timers or other objects used by kernel subsystems. So when the driver
> writer creates an kernel related object in the vmalloc space, he has
> to use the kernel mapping which is unmapped separate, right ?

This is the kernel mapping. The user mapping is unmapped when
the userspace munmaps.


> I can see your concern about the infinite stu^H^H^Hcreativity of
> driver writers, but I prefer not to go down that road and provide
> debug infrastructure for absurdities.


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