Messages in this thread | | | Date | Thu, 7 Jun 2012 23:02:49 +0200 | From | Andrea Arcangeli <> | Subject | Re: [ 08/82] mm: pmd_read_atomic: fix 32bit PAE pmd walk vs pmd_populate SMP race condition |
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On Thu, Jun 07, 2012 at 09:04:14PM +0200, Andrea Arcangeli wrote: > #ifndef CONFIG_TRANSPARENT_HUGEPAGE > +#define pmd_read_atomic pmd_read_atomic > static inline pmd_t pmd_read_atomic(pmd_t *pmdp) > { > pmdval_t ret; > @@ -74,11 +81,6 @@ static inline pmd_t pmd_read_atomic(pmd_t *pmdp) > > return (pmd_t) { ret }; > } > -#else /* CONFIG_TRANSPARENT_HUGEPAGE */ > -static inline pmd_t pmd_read_atomic(pmd_t *pmdp) > -{ > - return (pmd_t) { atomic64_read((atomic64_t *)pmdp) }; > -} > #endif /* CONFIG_TRANSPARENT_HUGEPAGE */ > > static inline void native_set_pte_atomic(pte_t *ptep, pte_t pte)
This actually wasn't safe because if the high part wasn't none and the low part was none, the pmd_none check would fail. I sent an updated version that will fix this hopefully for good and it turns out the same pmd_read_atomic will work for THP=n/y without need of cmpxchg8b even if it's slightly less obviously safe than if we used atomic64_read for THP=y. Still safe that is...
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