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    SubjectRe: [COUNTERPATCH] mm: avoid overflowing preempt_count() in mmu_take_all_locks()
    On Thu, 1 Apr 2010, Peter Zijlstra wrote:

    > I'm sure you dropped Ingo and Thomas by accident.
    > On Thu, 2010-04-01 at 12:40 +0300, Avi Kivity wrote:
    > > mmu_take_all_locks() takes a spinlock for each vma, which means we increase
    > > the preempt count by the number of vmas in an address space. Since the user
    > > controls the number of vmas, they can cause preempt_count to overflow.
    > >
    > > Fix by making mmu_take_all_locks() only disable preemption once by making
    > > the spinlocks preempt-neutral.
    > Right, so while this will get rid of the warning it doesn't make the
    > code any nicer, its still a massive !preempt latency spot.

    I'm not sure whether this is a real well done April 1st joke or if there
    is someone trying to secure the "bad taste patch of the month" price.

    Anyway, I don't see a reason why we can't convert those locks to
    mutexes and get rid of the whole preempt disabled region.



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