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    SubjectRe: [PATCH] make idr_remove_all() do removal -before- free_layer()
    On Sun, Mar 08, 2009 at 04:33:36PM +0100, Ingo Molnar wrote:
    >
    > * Paul E. McKenney <paulmck@linux.vnet.ibm.com> wrote:
    >
    > > The following patch fixes a problem in the IDR system, where
    > > an idr_remove_all() hands a data element to call_rcu() (via
    > > free_layer()) before making that data element inaccessible to
    > > new readers. This is very bad, and results in readers still
    > > having a reference to this data element at the end of the
    > > grace period. Tests on large machines that concurrently map
    > > and unmap user-space memory within the same multithreaded
    > > process result in crashes within about five minutes. Applying
    > > this patch increases the kernel's longevity to the
    > > three-to-eight-hour range.
    > >
    > > There appear to be other similar problems in
    > > idr_get_empty_slot() and sub_remove(), but I fixed the easy
    > > one in idr_remove_all() first. It is therefore no surprise
    > > that failures still occur.
    > >
    > > (Yes, and I did look at the relevant patch last year without
    > > spotting this one. Goes to show the value of testing as well
    > > as code review, I guess...)
    > >
    > > Nadia, Manfred, any thoughts?
    > >
    > > Located-by: Milton Miller II <miltonm@austin.ibm.com>
    > > Tested-by: Milton Miller II <miltonm@austin.ibm.com>
    > > Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
    >
    > Hm, looks like something we really want to see fixed in
    > 2.6.29-final, right?

    This was located in real testing, so I agree that it is pretty high
    priority. So this patch should go into 2.6.29.

    The priority of the remaining yet-as-unknown fixes depends on their
    complexity and risk.

    Thanx, Paul


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