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Commit deceb6cd authored by Hugh Dickins's avatar Hugh Dickins Committed by Linus Torvalds
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[PATCH] mm: follow_page with inner ptlock 



Final step in pushing down common core's page_table_lock.  follow_page no
longer wants caller to hold page_table_lock, uses pte_offset_map_lock itself;
and so no page_table_lock is taken in get_user_pages itself.

But get_user_pages (and get_futex_key) do then need follow_page to pin the
page for them: take Daniel's suggestion of bitflags to follow_page.

Need one for WRITE, another for TOUCH (it was the accessed flag before:
vanished along with check_user_page_readable, but surely get_numa_maps is
wrong to mark every page it finds as accessed), another for GET.

And another, ANON to dispose of untouched_anonymous_page: it seems silly for
that to descend a second time, let follow_page observe if there was no page
table and return ZERO_PAGE if so.  Fix minor bug in that: check VM_LOCKED -
make_pages_present ought to make readonly anonymous present.

Give get_numa_maps a cond_resched while we're there.

Signed-off-by: default avatarHugh Dickins <hugh@veritas.com>
Signed-off-by: default avatarAndrew Morton <akpm@osdl.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@osdl.org>
parent c34d1b4d

fs/proc/task_mmu.c

+1 −2
Original line number Diff line number Diff line
@@ -419,7 +419,6 @@ static struct numa_maps *get_numa_maps(const struct vm_area_struct *vma) 
	for_each_node(i)

		md->node[i] =0;



	spin_lock(&mm->page_table_lock);

 	for (vaddr = vma->vm_start; vaddr < vma->vm_end; vaddr += PAGE_SIZE) {

		page = follow_page(mm, vaddr, 0);

		if (page) {
@@ -434,8 +433,8 @@ static struct numa_maps *get_numa_maps(const struct vm_area_struct *vma) 
				md->anon++;

			md->node[page_to_nid(page)]++;

		}

		cond_resched();

	}

	spin_unlock(&mm->page_table_lock);

	return md;

}

include/linux/mm.h

+12 −8
Original line number Diff line number Diff line
@@ -938,14 +938,18 @@ static inline unsigned long vma_pages(struct vm_area_struct *vma) 
	return (vma->vm_end - vma->vm_start) >> PAGE_SHIFT;

}



extern struct vm_area_struct *find_extend_vma(struct mm_struct *mm, unsigned long addr);



extern struct page * vmalloc_to_page(void *addr);

extern unsigned long vmalloc_to_pfn(void *addr);

extern struct page * follow_page(struct mm_struct *mm, unsigned long address,

		int write);

int remap_pfn_range(struct vm_area_struct *, unsigned long,

		unsigned long, unsigned long, pgprot_t);

struct vm_area_struct *find_extend_vma(struct mm_struct *, unsigned long addr);

struct page *vmalloc_to_page(void *addr);

unsigned long vmalloc_to_pfn(void *addr);

int remap_pfn_range(struct vm_area_struct *, unsigned long addr,

			unsigned long pfn, unsigned long size, pgprot_t);



struct page *follow_page(struct mm_struct *, unsigned long address,

			unsigned int foll_flags);

#define FOLL_WRITE	0x01	/* check pte is writable */

#define FOLL_TOUCH	0x02	/* mark page accessed */

#define FOLL_GET	0x04	/* do get_page on page */

#define FOLL_ANON	0x08	/* give ZERO_PAGE if no pgtable */



#ifdef CONFIG_PROC_FS

void vm_stat_account(struct mm_struct *, unsigned long, struct file *, long);

kernel/futex.c

+2 −4
Original line number Diff line number Diff line
@@ -205,15 +205,13 @@ static int get_futex_key(unsigned long uaddr, union futex_key *key) 
	/*

	 * Do a quick atomic lookup first - this is the fastpath.

	 */

	spin_lock(&current->mm->page_table_lock);

	page = follow_page(mm, uaddr, 0);

	page = follow_page(mm, uaddr, FOLL_TOUCH|FOLL_GET);

	if (likely(page != NULL)) {

		key->shared.pgoff =

			page->index << (PAGE_CACHE_SHIFT - PAGE_SHIFT);

		spin_unlock(&current->mm->page_table_lock);

		put_page(page);

		return 0;

	}

	spin_unlock(&current->mm->page_table_lock);



	/*

	 * Do it the general way.

mm/memory.c

+71 −81
Original line number Diff line number Diff line
@@ -807,86 +807,82 @@ unsigned long zap_page_range(struct vm_area_struct *vma, unsigned long address, 


/*

 * Do a quick page-table lookup for a single page.

 * mm->page_table_lock must be held.

 */

struct page *follow_page(struct mm_struct *mm, unsigned long address, int write)

struct page *follow_page(struct mm_struct *mm, unsigned long address,

			unsigned int flags)

{

	pgd_t *pgd;

	pud_t *pud;

	pmd_t *pmd;

	pte_t *ptep, pte;

	spinlock_t *ptl;

	unsigned long pfn;

	struct page *page;



	page = follow_huge_addr(mm, address, write);

	if (! IS_ERR(page))

		return page;

	page = follow_huge_addr(mm, address, flags & FOLL_WRITE);

	if (!IS_ERR(page)) {

		BUG_ON(flags & FOLL_GET);

		goto out;

	}



	page = NULL;

	pgd = pgd_offset(mm, address);

	if (pgd_none(*pgd) || unlikely(pgd_bad(*pgd)))

		goto out;

		goto no_page_table;



	pud = pud_offset(pgd, address);

	if (pud_none(*pud) || unlikely(pud_bad(*pud)))

		goto out;

		goto no_page_table;

	

	pmd = pmd_offset(pud, address);

	if (pmd_none(*pmd) || unlikely(pmd_bad(*pmd)))

		goto no_page_table;



	if (pmd_huge(*pmd)) {

		BUG_ON(flags & FOLL_GET);

		page = follow_huge_pmd(mm, address, pmd, flags & FOLL_WRITE);

		goto out;

	if (pmd_huge(*pmd))

		return follow_huge_pmd(mm, address, pmd, write);

	}



	ptep = pte_offset_map(pmd, address);

	ptep = pte_offset_map_lock(mm, pmd, address, &ptl);

	if (!ptep)

		goto out;



	pte = *ptep;

	pte_unmap(ptep);

	if (pte_present(pte)) {

		if (write && !pte_write(pte))

			goto out;

	if (!pte_present(pte))

		goto unlock;

	if ((flags & FOLL_WRITE) && !pte_write(pte))

		goto unlock;

	pfn = pte_pfn(pte);

		if (pfn_valid(pfn)) {

	if (!pfn_valid(pfn))

		goto unlock;



	page = pfn_to_page(pfn);

			if (write && !pte_dirty(pte) &&!PageDirty(page))

	if (flags & FOLL_GET)

		get_page(page);

	if (flags & FOLL_TOUCH) {

		if ((flags & FOLL_WRITE) &&

		    !pte_dirty(pte) && !PageDirty(page))

			set_page_dirty(page);

		mark_page_accessed(page);

			return page;

	}

	}



unlock:

	pte_unmap_unlock(ptep, ptl);

out:

	return NULL;

}



static inline int

untouched_anonymous_page(struct mm_struct* mm, struct vm_area_struct *vma,

			 unsigned long address)

{

	pgd_t *pgd;

	pud_t *pud;

	pmd_t *pmd;



	/* Check if the vma is for an anonymous mapping. */

	if (vma->vm_ops && vma->vm_ops->nopage)

		return 0;



	/* Check if page directory entry exists. */

	pgd = pgd_offset(mm, address);

	if (pgd_none(*pgd) || unlikely(pgd_bad(*pgd)))

		return 1;



	pud = pud_offset(pgd, address);

	if (pud_none(*pud) || unlikely(pud_bad(*pud)))

		return 1;



	/* Check if page middle directory entry exists. */

	pmd = pmd_offset(pud, address);

	if (pmd_none(*pmd) || unlikely(pmd_bad(*pmd)))

		return 1;

	return page;



	/* There is a pte slot for 'address' in 'mm'. */

	return 0;

no_page_table:

	/*

	 * When core dumping an enormous anonymous area that nobody

	 * has touched so far, we don't want to allocate page tables.

	 */

	if (flags & FOLL_ANON) {

		page = ZERO_PAGE(address);

		if (flags & FOLL_GET)

			get_page(page);

		BUG_ON(flags & FOLL_WRITE);

	}

	return page;

}



int get_user_pages(struct task_struct *tsk, struct mm_struct *mm,
@@ -894,18 +890,19 @@ int get_user_pages(struct task_struct *tsk, struct mm_struct *mm, 
		struct page **pages, struct vm_area_struct **vmas)

{

	int i;

	unsigned int flags;

	unsigned int vm_flags;



	/* 

	 * Require read or write permissions.

	 * If 'force' is set, we only require the "MAY" flags.

	 */

	flags = write ? (VM_WRITE | VM_MAYWRITE) : (VM_READ | VM_MAYREAD);

	flags &= force ? (VM_MAYREAD | VM_MAYWRITE) : (VM_READ | VM_WRITE);

	vm_flags  = write ? (VM_WRITE | VM_MAYWRITE) : (VM_READ | VM_MAYREAD);

	vm_flags &= force ? (VM_MAYREAD | VM_MAYWRITE) : (VM_READ | VM_WRITE);

	i = 0;



	do {

		struct vm_area_struct *vma;

		unsigned int foll_flags;



		vma = find_extend_vma(mm, start);

		if (!vma && in_gate_area(tsk, start)) {
@@ -946,7 +943,7 @@ int get_user_pages(struct task_struct *tsk, struct mm_struct *mm, 
		}



		if (!vma || (vma->vm_flags & (VM_IO | VM_RESERVED))

				|| !(flags & vma->vm_flags))

				|| !(vm_flags & vma->vm_flags))

			return i ? : -EFAULT;



		if (is_vm_hugetlb_page(vma)) {
@@ -954,29 +951,25 @@ int get_user_pages(struct task_struct *tsk, struct mm_struct *mm, 
						&start, &len, i);

			continue;

		}

		spin_lock(&mm->page_table_lock);



		foll_flags = FOLL_TOUCH;

		if (pages)

			foll_flags |= FOLL_GET;

		if (!write && !(vma->vm_flags & VM_LOCKED) &&

		    (!vma->vm_ops || !vma->vm_ops->nopage))

			foll_flags |= FOLL_ANON;



		do {

			int write_access = write;

			struct page *page;



			cond_resched_lock(&mm->page_table_lock);

			while (!(page = follow_page(mm, start, write_access))) {

				int ret;



				/*

				 * Shortcut for anonymous pages. We don't want

				 * to force the creation of pages tables for

				 * insanely big anonymously mapped areas that

				 * nobody touched so far. This is important

				 * for doing a core dump for these mappings.

				 */

				if (!write && untouched_anonymous_page(mm,vma,start)) {

					page = ZERO_PAGE(start);

					break;

				}

				spin_unlock(&mm->page_table_lock);

				ret = __handle_mm_fault(mm, vma, start, write_access);

			if (write)

				foll_flags |= FOLL_WRITE;



			cond_resched();

			while (!(page = follow_page(mm, start, foll_flags))) {

				int ret;

				ret = __handle_mm_fault(mm, vma, start,

						foll_flags & FOLL_WRITE);

				/*

				 * The VM_FAULT_WRITE bit tells us that do_wp_page has

				 * broken COW when necessary, even if maybe_mkwrite
@@ -984,7 +977,7 @@ int get_user_pages(struct task_struct *tsk, struct mm_struct *mm, 
				 * subsequent page lookups as if they were reads.

				 */

				if (ret & VM_FAULT_WRITE)

					write_access = 0;

					foll_flags &= ~FOLL_WRITE;

				

				switch (ret & ~VM_FAULT_WRITE) {

				case VM_FAULT_MINOR:
@@ -1000,12 +993,10 @@ int get_user_pages(struct task_struct *tsk, struct mm_struct *mm, 
				default:

					BUG();

				}

				spin_lock(&mm->page_table_lock);

			}

			if (pages) {

				pages[i] = page;

				flush_dcache_page(page);

				page_cache_get(page);

			}

			if (vmas)

				vmas[i] = vma;
@@ -1013,7 +1004,6 @@ int get_user_pages(struct task_struct *tsk, struct mm_struct *mm, 
			start += PAGE_SIZE;

			len--;

		} while (len && start < vma->vm_end);

		spin_unlock(&mm->page_table_lock);

	} while (len);

	return i;

}

mm/nommu.c

+2 −1
Original line number Diff line number Diff line
@@ -1049,7 +1049,8 @@ struct vm_area_struct *find_vma(struct mm_struct *mm, unsigned long addr) 


EXPORT_SYMBOL(find_vma);



struct page * follow_page(struct mm_struct *mm, unsigned long addr, int write)

struct page *follow_page(struct mm_struct *mm, unsigned long address,

			unsigned int foll_flags)

{

	return NULL;

}