Messages in this thread | | | Date | Thu, 1 Apr 2010 18:07:03 +0200 | From | Andrea Arcangeli <> | Subject | Re: [COUNTERPATCH] mm: avoid overflowing preempt_count() in mmu_take_all_locks() |
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On Thu, Apr 01, 2010 at 05:56:02PM +0200, Peter Zijlstra wrote: > Another thing is mm->nr_ptes, that doens't appear to be properly > serialized, __pte_alloc() does ++ under mm->page_table_lock, but > free_pte_range() does -- which afaict isn't always with page_table_lock > held, it does however always seem to have mmap_sem for writing.
Not saying this is necessarily safe, but how can be that relevant with spinlock->mutex/rwsem conversion? Only thing that breaks with that conversion would be RCU (the very anon_vma rcu breaks because it rcu_read_lock disabling preempt and then takes the anon_vma->lock, that falls apart because taking the anon_vma->lock will imply a schedule), but nr_ptes is a write operation so it can't be protected by RCU.
> However __pte_alloc() callers do not in fact hold mmap_sem for writing.
As long as the mmap_sem readers always also take the page_table_lock we're safe.
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