[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, 18 insertions, 30 deletions

diff --git a/mm/fremap.c b/mm/fremap.c
index 49719a35769..d862be3bc3e 100644
--- a/mm/fremap.c
+++ b/mm/fremap.c
@@ -63,23 +63,20 @@ int install_page(struct mm_struct *mm, struct vm_area_struct *vma,
 	pud_t *pud;
 	pgd_t *pgd;
 	pte_t pte_val;
+	spinlock_t *ptl;
 
 	BUG_ON(vma->vm_flags & VM_RESERVED);
 
 	pgd = pgd_offset(mm, addr);
-	spin_lock(&mm->page_table_lock);
-	
 	pud = pud_alloc(mm, pgd, addr);
 	if (!pud)
-		goto err_unlock;
-
+		goto out;
 	pmd = pmd_alloc(mm, pud, addr);
 	if (!pmd)
-		goto err_unlock;
-
-	pte = pte_alloc_map(mm, pmd, addr);
+		goto out;
+	pte = pte_alloc_map_lock(mm, pmd, addr, &ptl);
 	if (!pte)
-		goto err_unlock;
+		goto out;
 
 	/*
 	 * This page may have been truncated. Tell the
@@ -89,10 +86,10 @@ int install_page(struct mm_struct *mm, struct vm_area_struct *vma,
 	inode = vma->vm_file->f_mapping->host;
 	size = (i_size_read(inode) + PAGE_CACHE_SIZE - 1) >> PAGE_CACHE_SHIFT;
 	if (!page->mapping || page->index >= size)
-		goto err_unlock;
+		goto unlock;
 	err = -ENOMEM;
 	if (page_mapcount(page) > INT_MAX/2)
-		goto err_unlock;
+		goto unlock;
 
 	if (pte_none(*pte) || !zap_pte(mm, vma, addr, pte))
 		inc_mm_counter(mm, file_rss);
@@ -101,17 +98,15 @@ int install_page(struct mm_struct *mm, struct vm_area_struct *vma,
 	set_pte_at(mm, addr, pte, mk_pte(page, prot));
 	page_add_file_rmap(page);
 	pte_val = *pte;
-	pte_unmap(pte);
 	update_mmu_cache(vma, addr, pte_val);
-
 	err = 0;
-err_unlock:
-	spin_unlock(&mm->page_table_lock);
+unlock:
+	pte_unmap_unlock(pte, ptl);
+out:
 	return err;
 }
 EXPORT_SYMBOL(install_page);
 
-
 /*
  * Install a file pte to a given virtual memory address, release any
  * previously existing mapping.
@@ -125,23 +120,20 @@ int install_file_pte(struct mm_struct *mm, struct vm_area_struct *vma,
 	pud_t *pud;
 	pgd_t *pgd;
 	pte_t pte_val;
+	spinlock_t *ptl;
 
 	BUG_ON(vma->vm_flags & VM_RESERVED);
 
 	pgd = pgd_offset(mm, addr);
-	spin_lock(&mm->page_table_lock);
-	
 	pud = pud_alloc(mm, pgd, addr);
 	if (!pud)
-		goto err_unlock;
-
+		goto out;
 	pmd = pmd_alloc(mm, pud, addr);
 	if (!pmd)
-		goto err_unlock;
-
-	pte = pte_alloc_map(mm, pmd, addr);
+		goto out;
+	pte = pte_alloc_map_lock(mm, pmd, addr, &ptl);
 	if (!pte)
-		goto err_unlock;
+		goto out;
 
 	if (!pte_none(*pte) && zap_pte(mm, vma, addr, pte)) {
 		update_hiwater_rss(mm);
@@ -150,17 +142,13 @@ int install_file_pte(struct mm_struct *mm, struct vm_area_struct *vma,
 
 	set_pte_at(mm, addr, pte, pgoff_to_pte(pgoff));
 	pte_val = *pte;
-	pte_unmap(pte);
 	update_mmu_cache(vma, addr, pte_val);
-	spin_unlock(&mm->page_table_lock);
-	return 0;
-
-err_unlock:
-	spin_unlock(&mm->page_table_lock);
+	pte_unmap_unlock(pte, ptl);
+	err = 0;
+out:
 	return err;
 }
 
-
 /***
  * sys_remap_file_pages - remap arbitrary pages of a shared backing store
  *                        file within an existing vma.