Messages in this thread |  | | | Date | Thu, 1 Apr 2010 13:04:04 +0200 (CEST) | | From | Thomas Gleixner <> | | Subject | Re: [COUNTERPATCH] mm: avoid overflowing preempt_count() in mmu_take_all_locks() |
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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.
Thanks,
tglx
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