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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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2
kernel/fork.c
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@ -255,7 +255,6 @@ static inline int dup_mmap(struct mm_struct *mm, struct mm_struct *oldmm)
/*
* Link in the new vma and copy the page table entries.
*/
spin_lock(&mm->page_table_lock);
*pprev = tmp;
pprev = &tmp->vm_next;
@ -265,7 +264,6 @@ static inline int dup_mmap(struct mm_struct *mm, struct mm_struct *oldmm)
mm->map_count++;
retval = copy_page_range(mm, oldmm, tmp);
spin_unlock(&mm->page_table_lock);
if (tmp->vm_ops && tmp->vm_ops->open)
tmp->vm_ops->open(tmp);