Re: [ 08/82] mm: pmd_read_atomic: fix 32bit PAE pmd walk vs pmd_populate SMP race condition
From: Andrea Arcangeli <hidden>
Date: 2012-06-07 21:03:15
Also in:
lkml
On Thu, Jun 07, 2012 at 09:04:14PM +0200, Andrea Arcangeli wrote:
quoted hunk ↗ jump to hunk
#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...