[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>

1 files changed, 0 insertions, 2 deletions

diff --git a/kernel/fork.c b/kernel/fork.c
index 2a587b3224e3..8a069612eac3 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -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);