Re: [COUNTERPATCH] mm: avoid overflowing preempt_count() in mmu_take_all_locks()

From: Avi Kivity
Date: Thu Apr 01 2010 - 07:10:22 EST

On 04/01/2010 01:31 PM, 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.

True. But this is a band-aid we can apply now while the correct fix is being worked out.

error compiling committee.c: too many arguments to function

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