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[PATCH] mm: ptd_alloc take ptlock

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Second step in pushing down the page_table_lock.  Remove the temporary
bridging hack from __pud_alloc, __pmd_alloc, __pte_alloc: expect callers not
to hold page_table_lock, whether it's on init_mm or a user mm; take
page_table_lock internally to check if a racing task already allocated.

Convert their callers from common code.  But avoid coming back to change them
again later: instead of moving the spin_lock(&mm->page_table_lock) down,
switch over to new macros pte_alloc_map_lock and pte_unmap_unlock, which
encapsulate the mapping+locking and unlocking+unmapping together, and in the
end may use alternatives to the mm page_table_lock itself.

These callers all hold mmap_sem (some exclusively, some not), so at no level
can a page table be whipped away from beneath them; and pte_alloc uses the
"atomic" pmd_present to test whether it needs to allocate.  It appears that on
all arches we can safely descend without page_table_lock.

Signed-off-by: Hugh Dickins <hugh@veritas.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
This commit is contained in:
Hugh Dickins
2005-10-29 18:16:23 -07:00
committed by Linus Torvalds
parent 1bb3630e89
commit c74df32c72
7 changed files with 90 additions and 135 deletions
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18
include/linux/mm.h
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@@ -779,10 +779,28 @@ static inline pmd_t *pmd_alloc(struct mm_struct *mm, pud_t *pud, unsigned long a
}
#endif /* CONFIG_MMU && !__ARCH_HAS_4LEVEL_HACK */
#define pte_offset_map_lock(mm, pmd, address, ptlp) \
({ \
spinlock_t *__ptl = &(mm)->page_table_lock; \
pte_t *__pte = pte_offset_map(pmd, address); \
*(ptlp) = __ptl; \
spin_lock(__ptl); \
__pte; \
})
#define pte_unmap_unlock(pte, ptl) do { \
spin_unlock(ptl); \
pte_unmap(pte); \
} while (0)
#define pte_alloc_map(mm, pmd, address) \
((unlikely(!pmd_present(*(pmd))) && __pte_alloc(mm, pmd, address))? \
NULL: pte_offset_map(pmd, address))
#define pte_alloc_map_lock(mm, pmd, address, ptlp) \
((unlikely(!pmd_present(*(pmd))) && __pte_alloc(mm, pmd, address))? \
NULL: pte_offset_map_lock(mm, pmd, address, ptlp))
#define pte_alloc_kernel(pmd, address) \
((unlikely(!pmd_present(*(pmd))) && __pte_alloc_kernel(pmd, address))? \
NULL: pte_offset_kernel(pmd, address))