Messages in this thread | | | Date | Mon, 22 May 2023 19:17:11 +0800 | Subject | Re: [PATCH 04/31] mm/pgtable: allow pte_offset_map[_lock]() to fail | From | Qi Zheng <> |
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Hi Hugh,
On 2023/5/22 12:53, Hugh Dickins wrote:
[...]
> > @@ -229,3 +231,57 @@ pmd_t pmdp_collapse_flush(struct vm_area_struct *vma, unsigned long address, > } > #endif > #endif /* CONFIG_TRANSPARENT_HUGEPAGE */ > + > +pte_t *__pte_offset_map(pmd_t *pmd, unsigned long addr, pmd_t *pmdvalp) > +{ > + pmd_t pmdval; > + > + /* rcu_read_lock() to be added later */ > + pmdval = pmdp_get_lockless(pmd); > + if (pmdvalp) > + *pmdvalp = pmdval; > + if (unlikely(pmd_none(pmdval) || is_pmd_migration_entry(pmdval))) > + goto nomap; > + if (unlikely(pmd_trans_huge(pmdval) || pmd_devmap(pmdval))) > + goto nomap;
Will the follow-up patch deal with the above situation specially? Otherwise, maybe it can be changed to the following check method?
if (unlikely(pmd_none(pmdval) || pmd_leaf(pmdval))) goto nomap;
> + if (unlikely(pmd_bad(pmdval))) { > + pmd_clear_bad(pmd); > + goto nomap; > + } > + return __pte_map(&pmdval, addr); > +nomap: > + /* rcu_read_unlock() to be added later */ > + return NULL; > +} > + > +pte_t *pte_offset_map_nolock(struct mm_struct *mm, pmd_t *pmd, > + unsigned long addr, spinlock_t **ptlp) > +{ > + pmd_t pmdval; > + pte_t *pte; > + > + pte = __pte_offset_map(pmd, addr, &pmdval); > + if (likely(pte)) > + *ptlp = pte_lockptr(mm, &pmdval); > + return pte; > +} > + > +pte_t *__pte_offset_map_lock(struct mm_struct *mm, pmd_t *pmd, > + unsigned long addr, spinlock_t **ptlp) > +{ > + spinlock_t *ptl; > + pmd_t pmdval; > + pte_t *pte; > +again: > + pte = __pte_offset_map(pmd, addr, &pmdval); > + if (unlikely(!pte)) > + return pte; > + ptl = pte_lockptr(mm, &pmdval); > + spin_lock(ptl); > + if (likely(pmd_same(pmdval, pmdp_get_lockless(pmd)))) { > + *ptlp = ptl; > + return pte; > + } > + pte_unmap_unlock(pte, ptl); > + goto again; > +}
-- Thanks, Qi
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