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    SubjectRe: [PATCH] mm: fix lazy vmap purging (use-after-free error)
    On Mon, Feb 23, 2009 at 11:10:09AM -0800, Andrew Morton wrote:
    > On Mon, 23 Feb 2009 08:17:26 -0800 "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> wrote:
    >
    > > On Tue, Feb 24, 2009 at 12:29:36AM +1100, Nick Piggin wrote:
    > > > On Monday 23 February 2009 16:17:09 Paul E. McKenney wrote:
    > > >
    > > > > The boot CPU runs in the context of its idle thread during boot-up.
    > > > > During this time, idle_cpu(0) will always return nonzero, which will
    > > > > fool Classic and Hierarchical RCU into deciding that a large chunk of
    > > > > the boot-up sequence is a big long quiescent state. This in turn causes
    > > > > RCU to prematurely end grace periods during this time.
    > > > >
    > > > > This patch creates a new global variable that is set to 1 just before
    > > > > the boot CPU first enters the scheduler, after which the idle task
    > > > > really is idle.
    > > >
    > > > Nice work all (btw. if this patch goes in rather than using system_state,
    > > > then please make the variable __read_mostly).
    > >
    > > Hmmm... I misread this and made system_state be __read_mostly. Let
    > > me know if this is bad, easy to fix if needed.
    >
    > Please don't use system_state. The whole thing is just bad design.
    > It's a global variable, breaks encapsulation, creates interactions etc.
    > CS-101 stuff.

    OK. Would it help if I wrapped an accessor function around system_state?

    I do need some sort of global state if I am to solve this problem. ;-)

    Thanx, Paul


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