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    SubjectRe: [RFC][PATCH] linux-2.5.34_vsyscall_A0
    Linus Torvalds wrote:
    >
    > On Fri, 18 Oct 2002, Andrea Arcangeli wrote:
    >
    > > On Fri, Oct 18, 2002 at 09:45:41AM -0700, george anzinger wrote:
    > > > Stephen Hemminger wrote:
    > > > > current cpu (and maybe current pid) somehow. And it would be possible
    > > > > to avoid preemption while in a vsyscall text page, some other Unix
    > > > > variants do this to implement portions of the thread library in kernel
    > > > > provided user text pages.
    > > > >
    > > > Now there is an idea! Lock preemption in user space if and
    > >
    > > sounds not good to me, you would miss a wakeup and you would delay the
    > > schedule of 1/HZ in the worst (close to the common) case.
    >
    > That's not the real problem.
    >
    > The real problem is that somebody can jump into the middle of a function
    > (or even into the middle of an instruction), causing the function to do
    > something totally different from the intended effect.
    >
    > In particular, it can cause the function to loop forever.
    >
    > If you disable preemption of user space, you now killed the machine.
    >
    > In short - others may do it, but it's a total _DISASTER_ from a security
    > and stability standpoint. Don't go there.

    Oops, hadn't thought of that. Back out, undo, etc. :)

    --
    George Anzinger george@mvista.com
    High-res-timers:
    http://sourceforge.net/projects/high-res-timers/
    Preemption patch:
    http://www.kernel.org/pub/linux/kernel/people/rml
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