[PATCH] mm: ptd_alloc take ptlock
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>
diff --git a/mm/mremap.c b/mm/mremap.c
index 616facc..8de77b6 100644
--- a/mm/mremap.c
+++ b/mm/mremap.c
@@ -28,9 +28,6 @@
pud_t *pud;
pmd_t *pmd;
- /*
- * We don't need page_table_lock: we have mmap_sem exclusively.
- */
pgd = pgd_offset(mm, addr);
if (pgd_none_or_clear_bad(pgd))
return NULL;
@@ -50,25 +47,20 @@
{
pgd_t *pgd;
pud_t *pud;
- pmd_t *pmd = NULL;
+ pmd_t *pmd;
- /*
- * We do need page_table_lock: because allocators expect that.
- */
- spin_lock(&mm->page_table_lock);
pgd = pgd_offset(mm, addr);
pud = pud_alloc(mm, pgd, addr);
if (!pud)
- goto out;
+ return NULL;
pmd = pmd_alloc(mm, pud, addr);
if (!pmd)
- goto out;
+ return NULL;
if (!pmd_present(*pmd) && __pte_alloc(mm, pmd, addr))
- pmd = NULL;
-out:
- spin_unlock(&mm->page_table_lock);
+ return NULL;
+
return pmd;
}
@@ -80,6 +72,7 @@
struct address_space *mapping = NULL;
struct mm_struct *mm = vma->vm_mm;
pte_t *old_pte, *new_pte, pte;
+ spinlock_t *old_ptl;
if (vma->vm_file) {
/*
@@ -95,9 +88,8 @@
new_vma->vm_truncate_count = 0;
}
- spin_lock(&mm->page_table_lock);
- old_pte = pte_offset_map(old_pmd, old_addr);
- new_pte = pte_offset_map_nested(new_pmd, new_addr);
+ old_pte = pte_offset_map_lock(mm, old_pmd, old_addr, &old_ptl);
+ new_pte = pte_offset_map_nested(new_pmd, new_addr);
for (; old_addr < old_end; old_pte++, old_addr += PAGE_SIZE,
new_pte++, new_addr += PAGE_SIZE) {
@@ -110,8 +102,7 @@
}
pte_unmap_nested(new_pte - 1);
- pte_unmap(old_pte - 1);
- spin_unlock(&mm->page_table_lock);
+ pte_unmap_unlock(old_pte - 1, old_ptl);
if (mapping)
spin_unlock(&mapping->i_mmap_lock);
}