[PATCH] mm: arches skip ptlock

Convert those few architectures which are calling pud_alloc, pmd_alloc,
pte_alloc_map on a user mm, not to take the page_table_lock first, nor drop it
after.  Each of these can continue to use pte_alloc_map, no need to change
over to pte_alloc_map_lock, they're neither racy nor swappable.

In the sparc64 io_remap_pfn_range, flush_tlb_range then falls outside of the
page_table_lock: that's okay, on sparc64 it's like flush_tlb_mm, and that has
always been called from outside of page_table_lock in dup_mmap.

Signed-off-by: Hugh Dickins <hugh@veritas.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

arch/arm/mm/mm-armv.c

@@ -179,11 +179,6 @@ pgd_t *get_pgd_slow(struct mm_struct *mm)
 	clean_dcache_area(new_pgd, PTRS_PER_PGD * sizeof(pgd_t));
 
 	if (!vectors_high()) {
-		/*
-		 * This lock is here just to satisfy pmd_alloc and pte_lock
-		 */
-		spin_lock(&mm->page_table_lock);
-
 		/*
 		 * On ARM, first page must always be allocated since it
 		 * contains the machine vectors.
@@ -201,23 +196,14 @@ pgd_t *get_pgd_slow(struct mm_struct *mm)
 		set_pte(new_pte, *init_pte);
 		pte_unmap_nested(init_pte);
 		pte_unmap(new_pte);
-
-		spin_unlock(&mm->page_table_lock);
 	}
 
 	return new_pgd;
 
 no_pte:
-	spin_unlock(&mm->page_table_lock);
 	pmd_free(new_pmd);
-	free_pages((unsigned long)new_pgd, 2);
-	return NULL;
-
 no_pmd:
-	spin_unlock(&mm->page_table_lock);
 	free_pages((unsigned long)new_pgd, 2);
-	return NULL;
-
 no_pgd:
 	return NULL;
 }

arch/arm26/mm/memc.c

@@ -78,12 +78,6 @@ pgd_t *get_pgd_slow(struct mm_struct *mm)
 	if (!new_pgd)
 		goto no_pgd;
 
-	/*
-	 * This lock is here just to satisfy pmd_alloc and pte_lock
-         * FIXME: I bet we could avoid taking it pretty much altogether
-	 */
-	spin_lock(&mm->page_table_lock);
-
 	/*
 	 * On ARM, first page must always be allocated since it contains
 	 * the machine vectors.
@@ -113,23 +107,14 @@ pgd_t *get_pgd_slow(struct mm_struct *mm)
 	memcpy(new_pgd + FIRST_KERNEL_PGD_NR, init_pgd + FIRST_KERNEL_PGD_NR,
 		(PTRS_PER_PGD - FIRST_KERNEL_PGD_NR) * sizeof(pgd_t));
 
-	spin_unlock(&mm->page_table_lock);
-
 	/* update MEMC tables */
 	cpu_memc_update_all(new_pgd);
 	return new_pgd;
 
 no_pte:
-	spin_unlock(&mm->page_table_lock);
 	pmd_free(new_pmd);
-	free_pgd_slow(new_pgd);
-	return NULL;
-
 no_pmd:
-	spin_unlock(&mm->page_table_lock);
 	free_pgd_slow(new_pgd);
-	return NULL;
-
 no_pgd:
 	return NULL;
 }

arch/sparc/mm/generic.c

@@ -81,9 +81,8 @@ int io_remap_pfn_range(struct vm_area_struct *vma, unsigned long from,
 	dir = pgd_offset(mm, from);
 	flush_cache_range(vma, beg, end);
 
-	spin_lock(&mm->page_table_lock);
 	while (from < end) {
-		pmd_t *pmd = pmd_alloc(current->mm, dir, from);
+		pmd_t *pmd = pmd_alloc(mm, dir, from);
 		error = -ENOMEM;
 		if (!pmd)
 			break;
@@ -93,7 +92,6 @@ int io_remap_pfn_range(struct vm_area_struct *vma, unsigned long from,
 		from = (from + PGDIR_SIZE) & PGDIR_MASK;
 		dir++;
 	}
-	spin_unlock(&mm->page_table_lock);
 
 	flush_tlb_range(vma, beg, end);
 	return error;

arch/sparc64/mm/generic.c

@@ -135,9 +135,8 @@ int io_remap_pfn_range(struct vm_area_struct *vma, unsigned long from,
 	dir = pgd_offset(mm, from);
 	flush_cache_range(vma, beg, end);
 
-	spin_lock(&mm->page_table_lock);
 	while (from < end) {
-		pud_t *pud = pud_alloc(current->mm, dir, from);
+		pud_t *pud = pud_alloc(mm, dir, from);
 		error = -ENOMEM;
 		if (!pud)
 			break;
@@ -147,8 +146,7 @@ int io_remap_pfn_range(struct vm_area_struct *vma, unsigned long from,
 		from = (from + PGDIR_SIZE) & PGDIR_MASK;
 		dir++;
 	}
-	flush_tlb_range(vma, beg, end);
-	spin_unlock(&mm->page_table_lock);
 
+	flush_tlb_range(vma, beg, end);
 	return error;
 }

arch/um/kernel/skas/mmu.c

@@ -28,7 +28,6 @@ static int init_stub_pte(struct mm_struct *mm, unsigned long proc,
 	pmd_t *pmd;
 	pte_t *pte;
 
-	spin_lock(&mm->page_table_lock);
 	pgd = pgd_offset(mm, proc);
 	pud = pud_alloc(mm, pgd, proc);
 	if (!pud)
@@ -63,15 +62,13 @@ static int init_stub_pte(struct mm_struct *mm, unsigned long proc,
 	*pte = mk_pte(virt_to_page(kernel), __pgprot(_PAGE_PRESENT));
 	*pte = pte_mkexec(*pte);
 	*pte = pte_wrprotect(*pte);
-	spin_unlock(&mm->page_table_lock);
 	return(0);
 
  out_pmd:
 	pud_free(pud);
  out_pte:
 	pmd_free(pmd);
  out:
-	spin_unlock(&mm->page_table_lock);
 	return(-ENOMEM);
 }