[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>

4 files changed, 67 insertions, 124 deletions

diff --git a/mm/fremap.c b/mm/fremap.c
index 49719a35769a..d862be3bc3e3 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.
diff --git a/mm/hugetlb.c b/mm/hugetlb.c
index ac5f044bf514..ea0826ff2663 100644
--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c
@@ -277,12 +277,15 @@ int copy_hugetlb_page_range(struct mm_struct *dst, struct mm_struct *src,
 	unsigned long addr;
 
 	for (addr = vma->vm_start; addr < vma->vm_end; addr += HPAGE_SIZE) {
+		src_pte = huge_pte_offset(src, addr);
+		if (!src_pte)
+			continue;
 		dst_pte = huge_pte_alloc(dst, addr);
 		if (!dst_pte)
 			goto nomem;
+		spin_lock(&dst->page_table_lock);
 		spin_lock(&src->page_table_lock);
-		src_pte = huge_pte_offset(src, addr);
-		if (src_pte && !pte_none(*src_pte)) {
+		if (!pte_none(*src_pte)) {
 			entry = *src_pte;
 			ptepage = pte_page(entry);
 			get_page(ptepage);
@@ -290,6 +293,7 @@ int copy_hugetlb_page_range(struct mm_struct *dst, struct mm_struct *src,
 			set_huge_pte_at(dst, addr, dst_pte, entry);
 		}
 		spin_unlock(&src->page_table_lock);
+		spin_unlock(&dst->page_table_lock);
 	}
 	return 0;
 
@@ -354,7 +358,6 @@ int hugetlb_prefault(struct address_space *mapping, struct vm_area_struct *vma)
 
 	hugetlb_prefault_arch_hook(mm);
 
-	spin_lock(&mm->page_table_lock);
 	for (addr = vma->vm_start; addr < vma->vm_end; addr += HPAGE_SIZE) {
 		unsigned long idx;
 		pte_t *pte = huge_pte_alloc(mm, addr);
@@ -389,11 +392,12 @@ int hugetlb_prefault(struct address_space *mapping, struct vm_area_struct *vma)
 				goto out;
 			}
 		}
+		spin_lock(&mm->page_table_lock);
 		add_mm_counter(mm, file_rss, HPAGE_SIZE / PAGE_SIZE);
 		set_huge_pte_at(mm, addr, pte, make_huge_pte(vma, page));
+		spin_unlock(&mm->page_table_lock);
 	}
 out:
-	spin_unlock(&mm->page_table_lock);
 	return ret;
 }
 
diff --git a/mm/memory.c b/mm/memory.c
index 4bdd1186b43b..a40e4b1cee4f 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -282,14 +282,11 @@ void free_pgtables(struct mmu_gather **tlb, struct vm_area_struct *vma,
 
 int __pte_alloc(struct mm_struct *mm, pmd_t *pmd, unsigned long address)
 {
-	struct page *new;
-
-	spin_unlock(&mm->page_table_lock);
-	new = pte_alloc_one(mm, address);
-	spin_lock(&mm->page_table_lock);
+	struct page *new = pte_alloc_one(mm, address);
 	if (!new)
 		return -ENOMEM;
 
+	spin_lock(&mm->page_table_lock);
 	if (pmd_present(*pmd))		/* Another has populated it */
 		pte_free(new);
 	else {
@@ -297,6 +294,7 @@ int __pte_alloc(struct mm_struct *mm, pmd_t *pmd, unsigned long address)
 		inc_page_state(nr_page_table_pages);
 		pmd_populate(mm, pmd, new);
 	}
+	spin_unlock(&mm->page_table_lock);
 	return 0;
 }
 
@@ -344,9 +342,6 @@ void print_bad_pte(struct vm_area_struct *vma, pte_t pte, unsigned long vaddr)
  * copy one vm_area from one task to the other. Assumes the page tables
  * already present in the new task to be cleared in the whole range
  * covered by this vma.
- *
- * dst->page_table_lock is held on entry and exit,
- * but may be dropped within p[mg]d_alloc() and pte_alloc_map().
  */
 
 static inline void
@@ -419,17 +414,19 @@ static int copy_pte_range(struct mm_struct *dst_mm, struct mm_struct *src_mm,
 		unsigned long addr, unsigned long end)
 {
 	pte_t *src_pte, *dst_pte;
+	spinlock_t *src_ptl, *dst_ptl;
 	int progress = 0;
 	int rss[2];
 
 again:
 	rss[1] = rss[0] = 0;
-	dst_pte = pte_alloc_map(dst_mm, dst_pmd, addr);
+	dst_pte = pte_alloc_map_lock(dst_mm, dst_pmd, addr, &dst_ptl);
 	if (!dst_pte)
 		return -ENOMEM;
 	src_pte = pte_offset_map_nested(src_pmd, addr);
+	src_ptl = &src_mm->page_table_lock;
+	spin_lock(src_ptl);
 
-	spin_lock(&src_mm->page_table_lock);
 	do {
 		/*
 		 * We are holding two locks at this point - either of them
@@ -438,8 +435,8 @@ again:
 		if (progress >= 32) {
 			progress = 0;
 			if (need_resched() ||
-			    need_lockbreak(&src_mm->page_table_lock) ||
-			    need_lockbreak(&dst_mm->page_table_lock))
+			    need_lockbreak(src_ptl) ||
+			    need_lockbreak(dst_ptl))
 				break;
 		}
 		if (pte_none(*src_pte)) {
@@ -449,12 +446,12 @@ again:
 		copy_one_pte(dst_mm, src_mm, dst_pte, src_pte, vma, addr, rss);
 		progress += 8;
 	} while (dst_pte++, src_pte++, addr += PAGE_SIZE, addr != end);
-	spin_unlock(&src_mm->page_table_lock);
 
+	spin_unlock(src_ptl);
 	pte_unmap_nested(src_pte - 1);
-	pte_unmap(dst_pte - 1);
 	add_mm_rss(dst_mm, rss[0], rss[1]);
-	cond_resched_lock(&dst_mm->page_table_lock);
+	pte_unmap_unlock(dst_pte - 1, dst_ptl);
+	cond_resched();
 	if (addr != end)
 		goto again;
 	return 0;
@@ -1049,8 +1046,9 @@ static int zeromap_pte_range(struct mm_struct *mm, pmd_t *pmd,
 			unsigned long addr, unsigned long end, pgprot_t prot)
 {
 	pte_t *pte;
+	spinlock_t *ptl;
 
-	pte = pte_alloc_map(mm, pmd, addr);
+	pte = pte_alloc_map_lock(mm, pmd, addr, &ptl);
 	if (!pte)
 		return -ENOMEM;
 	do {
@@ -1062,7 +1060,7 @@ static int zeromap_pte_range(struct mm_struct *mm, pmd_t *pmd,
 		BUG_ON(!pte_none(*pte));
 		set_pte_at(mm, addr, pte, zero_pte);
 	} while (pte++, addr += PAGE_SIZE, addr != end);
-	pte_unmap(pte - 1);
+	pte_unmap_unlock(pte - 1, ptl);
 	return 0;
 }
 
@@ -1112,14 +1110,12 @@ int zeromap_page_range(struct vm_area_struct *vma,
 	BUG_ON(addr >= end);
 	pgd = pgd_offset(mm, addr);
 	flush_cache_range(vma, addr, end);
-	spin_lock(&mm->page_table_lock);
 	do {
 		next = pgd_addr_end(addr, end);
 		err = zeromap_pud_range(mm, pgd, addr, next, prot);
 		if (err)
 			break;
 	} while (pgd++, addr = next, addr != end);
-	spin_unlock(&mm->page_table_lock);
 	return err;
 }
 
@@ -1133,8 +1129,9 @@ static int remap_pte_range(struct mm_struct *mm, pmd_t *pmd,
 			unsigned long pfn, pgprot_t prot)
 {
 	pte_t *pte;
+	spinlock_t *ptl;
 
-	pte = pte_alloc_map(mm, pmd, addr);
+	pte = pte_alloc_map_lock(mm, pmd, addr, &ptl);
 	if (!pte)
 		return -ENOMEM;
 	do {
@@ -1142,7 +1139,7 @@ static int remap_pte_range(struct mm_struct *mm, pmd_t *pmd,
 		set_pte_at(mm, addr, pte, pfn_pte(pfn, prot));
 		pfn++;
 	} while (pte++, addr += PAGE_SIZE, addr != end);
-	pte_unmap(pte - 1);
+	pte_unmap_unlock(pte - 1, ptl);
 	return 0;
 }
 
@@ -1210,7 +1207,6 @@ int remap_pfn_range(struct vm_area_struct *vma, unsigned long addr,
 	pfn -= addr >> PAGE_SHIFT;
 	pgd = pgd_offset(mm, addr);
 	flush_cache_range(vma, addr, end);
-	spin_lock(&mm->page_table_lock);
 	do {
 		next = pgd_addr_end(addr, end);
 		err = remap_pud_range(mm, pgd, addr, next,
@@ -1218,7 +1214,6 @@ int remap_pfn_range(struct vm_area_struct *vma, unsigned long addr,
 		if (err)
 			break;
 	} while (pgd++, addr = next, addr != end);
-	spin_unlock(&mm->page_table_lock);
 	return err;
 }
 EXPORT_SYMBOL(remap_pfn_range);
@@ -1985,17 +1980,9 @@ static int do_file_page(struct mm_struct *mm, struct vm_area_struct *vma,
  * with external mmu caches can use to update those (ie the Sparc or
  * PowerPC hashed page tables that act as extended TLBs).
  *
- * Note the "page_table_lock". It is to protect against kswapd removing
- * pages from under us. Note that kswapd only ever _removes_ pages, never
- * adds them. As such, once we have noticed that the page is not present,
- * we can drop the lock early.
- *
- * The adding of pages is protected by the MM semaphore (which we hold),
- * so we don't need to worry about a page being suddenly been added into
- * our VM.
- *
- * We enter with the pagetable spinlock held, we are supposed to
- * release it when done.
+ * We enter with non-exclusive mmap_sem (to exclude vma changes,
+ * but allow concurrent faults), and pte mapped but not yet locked.
+ * We return with mmap_sem still held, but pte unmapped and unlocked.
  */
 static inline int handle_pte_fault(struct mm_struct *mm,
 		struct vm_area_struct *vma, unsigned long address,
@@ -2003,6 +1990,7 @@ static inline int handle_pte_fault(struct mm_struct *mm,
 {
 	pte_t entry;
 
+	spin_lock(&mm->page_table_lock);
 	entry = *pte;
 	if (!pte_present(entry)) {
 		if (pte_none(entry)) {
@@ -2051,30 +2039,18 @@ int __handle_mm_fault(struct mm_struct *mm, struct vm_area_struct *vma,
 	if (unlikely(is_vm_hugetlb_page(vma)))
 		return hugetlb_fault(mm, vma, address, write_access);
 
-	/*
-	 * We need the page table lock to synchronize with kswapd
-	 * and the SMP-safe atomic PTE updates.
-	 */
 	pgd = pgd_offset(mm, address);
-	spin_lock(&mm->page_table_lock);
-
 	pud = pud_alloc(mm, pgd, address);
 	if (!pud)
-		goto oom;
-
+		return VM_FAULT_OOM;
 	pmd = pmd_alloc(mm, pud, address);
 	if (!pmd)
-		goto oom;
-
+		return VM_FAULT_OOM;
 	pte = pte_alloc_map(mm, pmd, address);
 	if (!pte)
-		goto oom;
-	
-	return handle_pte_fault(mm, vma, address, pte, pmd, write_access);
+		return VM_FAULT_OOM;
 
- oom:
-	spin_unlock(&mm->page_table_lock);
-	return VM_FAULT_OOM;
+	return handle_pte_fault(mm, vma, address, pte, pmd, write_access);
 }
 
 #ifndef __PAGETABLE_PUD_FOLDED
@@ -2084,24 +2060,16 @@ int __handle_mm_fault(struct mm_struct *mm, struct vm_area_struct *vma,
  */
 int __pud_alloc(struct mm_struct *mm, pgd_t *pgd, unsigned long address)
 {
-	pud_t *new;
-
-	if (mm != &init_mm)		/* Temporary bridging hack */
-		spin_unlock(&mm->page_table_lock);
-	new = pud_alloc_one(mm, address);
-	if (!new) {
-		if (mm != &init_mm)	/* Temporary bridging hack */
-			spin_lock(&mm->page_table_lock);
+	pud_t *new = pud_alloc_one(mm, address);
+	if (!new)
 		return -ENOMEM;
-	}
 
 	spin_lock(&mm->page_table_lock);
 	if (pgd_present(*pgd))		/* Another has populated it */
 		pud_free(new);
 	else
 		pgd_populate(mm, pgd, new);
-	if (mm == &init_mm)		/* Temporary bridging hack */
-		spin_unlock(&mm->page_table_lock);
+	spin_unlock(&mm->page_table_lock);
 	return 0;
 }
 #endif /* __PAGETABLE_PUD_FOLDED */
@@ -2113,16 +2081,9 @@ int __pud_alloc(struct mm_struct *mm, pgd_t *pgd, unsigned long address)
  */
 int __pmd_alloc(struct mm_struct *mm, pud_t *pud, unsigned long address)
 {
-	pmd_t *new;
-
-	if (mm != &init_mm)		/* Temporary bridging hack */
-		spin_unlock(&mm->page_table_lock);
-	new = pmd_alloc_one(mm, address);
-	if (!new) {
-		if (mm != &init_mm)	/* Temporary bridging hack */
-			spin_lock(&mm->page_table_lock);
+	pmd_t *new = pmd_alloc_one(mm, address);
+	if (!new)
 		return -ENOMEM;
-	}
 
 	spin_lock(&mm->page_table_lock);
 #ifndef __ARCH_HAS_4LEVEL_HACK
@@ -2136,8 +2097,7 @@ int __pmd_alloc(struct mm_struct *mm, pud_t *pud, unsigned long address)
 	else
 		pgd_populate(mm, pud, new);
 #endif /* __ARCH_HAS_4LEVEL_HACK */
-	if (mm == &init_mm)		/* Temporary bridging hack */
-		spin_unlock(&mm->page_table_lock);
+	spin_unlock(&mm->page_table_lock);
 	return 0;
 }
 #endif /* __PAGETABLE_PMD_FOLDED */
diff --git a/mm/mremap.c b/mm/mremap.c
index 616facc3d28a..8de77b632a20 100644
--- a/mm/mremap.c
+++ b/mm/mremap.c
@@ -28,9 +28,6 @@ static pmd_t *get_old_pmd(struct mm_struct *mm, unsigned long addr)
 	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 @@ static pmd_t *alloc_new_pmd(struct mm_struct *mm, unsigned long addr)
 {
 	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 @@ static void move_ptes(struct vm_area_struct *vma, pmd_t *old_pmd,
 	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 @@ static void move_ptes(struct vm_area_struct *vma, pmd_t *old_pmd,
 			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 @@ static void move_ptes(struct vm_area_struct *vma, pmd_t *old_pmd,
 	}
 
 	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);
 }