path: root/mm/mlock.c

/*
 *	linux/mm/mlock.c
 *
 *  (C) Copyright 1995 Linus Torvalds
 *  (C) Copyright 2002 Christoph Hellwig
 */

#include <linux/capability.h>
#include <linux/mman.h>
#include <linux/mm.h>
#include <linux/swap.h>
#include <linux/swapops.h>
#include <linux/pagemap.h>
#include <linux/pagevec.h>
#include <linux/mempolicy.h>
#include <linux/syscalls.h>
#include <linux/sched.h>
#include <linux/export.h>
#include <linux/rmap.h>
#include <linux/mmzone.h>
#include <linux/hugetlb.h>
#include <linux/memcontrol.h>
#include <linux/mm_inline.h>

#include "internal.h"

int can_do_mlock(void)
{
	if (capable(CAP_IPC_LOCK))
		return 1;
	if (rlimit(RLIMIT_MEMLOCK) != 0)
		return 1;
	return 0;
}
EXPORT_SYMBOL(can_do_mlock);

/*
 * Mlocked pages are marked with PageMlocked() flag for efficient testing
 * in vmscan and, possibly, the fault path; and to support semi-accurate
 * statistics.
 *
 * An mlocked page [PageMlocked(page)] is unevictable.  As such, it will
 * be placed on the LRU "unevictable" list, rather than the [in]active lists.
 * The unevictable list is an LRU sibling list to the [in]active lists.
 * PageUnevictable is set to indicate the unevictable state.
 *
 * When lazy mlocking via vmscan, it is important to ensure that the
 * vma's VM_LOCKED status is not concurrently being modified, otherwise we
 * may have mlocked a page that is being munlocked. So lazy mlock must take
 * the mmap_sem for read, and verify that the vma really is locked
 * (see mm/rmap.c).
 */

/*
 *  LRU accounting for clear_page_mlock()
 */
void clear_page_mlock(struct page *page)
{
	if (!TestClearPageMlocked(page))
		return;

	mod_zone_page_state(page_zone(page), NR_MLOCK,
			    -hpage_nr_pages(page));
	count_vm_event(UNEVICTABLE_PGCLEARED);
	if (!isolate_lru_page(page)) {
		putback_lru_page(page);
	} else {
		/*
		 * We lost the race. the page already moved to evictable list.
		 */
		if (PageUnevictable(page))
			count_vm_event(UNEVICTABLE_PGSTRANDED);
	}
}

/*
 * Mark page as mlocked if not already.
 * If page on LRU, isolate and putback to move to unevictable list.
 */
void mlock_vma_page(struct page *page)
{
	/* Serialize with page migration */
	BUG_ON(!PageLocked(page));

	if (!TestSetPageMlocked(page)) {
		mod_zone_page_state(page_zone(page), NR_MLOCK,
				    hpage_nr_pages(page));
		count_vm_event(UNEVICTABLE_PGMLOCKED);
		if (!isolate_lru_page(page))
			putback_lru_page(page);
	}
}

/*
 * Isolate a page from LRU with optional get_page() pin.
 * Assumes lru_lock already held and page already pinned.
 */
static bool __munlock_isolate_lru_page(struct page *page, bool getpage)
{
	if (PageLRU(page)) {
		struct lruvec *lruvec;

		lruvec = mem_cgroup_page_lruvec(page, page_zone(page));
		if (getpage)
			get_page(page);
		ClearPageLRU(page);
		del_page_from_lru_list(page, lruvec, page_lru(page));
		return true;
	}

	return false;
}

/*
 * Finish munlock after successful page isolation
 *
 * Page must be locked. This is a wrapper for try_to_munlock()
 * and putback_lru_page() with munlock accounting.
 */
static void __munlock_isolated_page(struct page *page)
{
	int ret = SWAP_AGAIN;

	/*
	 * Optimization: if the page was mapped just once, that's our mapping
	 * and we don't need to check all the other vmas.
	 */
	if (page_mapcount(page) > 1)
		ret = try_to_munlock(page);

	/* Did try_to_unlock() succeed or punt? */
	if (ret != SWAP_MLOCK)
		count_vm_event(UNEVICTABLE_PGMUNLOCKED);

	putback_lru_page(page);
}

/*
 * Accounting for page isolation fail during munlock
 *
 * Performs accounting when page isolation fails in munlock. There is nothing
 * else to do because it means some other task has already removed the page
 * from the LRU. putback_lru_page() will take care of removing the page from
 * the unevictable list, if necessary. vmscan [page_referenced()] will move
 * the page back to the unevictable list if some other vma has it mlocked.
 */
static void __munlock_isolation_failed(struct page *page)
{
	if (PageUnevictable(page))
		__count_vm_event(UNEVICTABLE_PGSTRANDED);
	else
		__count_vm_event(UNEVICTABLE_PGMUNLOCKED);
}

/**
 * munlock_vma_page - munlock a vma page
 * @page - page to be unlocked, either a normal page or THP page head
 *
 * returns the size of the page as a page mask (0 for normal page,
 *         HPAGE_PMD_NR - 1 for THP head page)
 *
 * called from munlock()/munmap() path with page supposedly on the LRU.
 * When we munlock a page, because the vma where we found the page is being
 * munlock()ed or munmap()ed, we want to check whether other vmas hold the
 * page locked so that we can leave it on the unevictable lru list and not
 * bother vmscan with it.  However, to walk the page's rmap list in
 * try_to_munlock() we must isolate the page from the LRU.  If some other
 * task has removed the page from the LRU, we won't be able to do that.
 * So we clear the PageMlocked as we might not get another chance.  If we
 * can't isolate the page, we leave it for putback_lru_page() and vmscan
 * [page_referenced()/try_to_unmap()] to deal with.
 */
unsigned int munlock_vma_page(struct page *page)
{
	unsigned int nr_pages;
	struct zone *zone = page_zone(page);

	/* For try_to_munlock() and to serialize with page migration */
	BUG_ON(!PageLocked(page));

	/*
	 * Serialize with any parallel __split_huge_page_refcount() which
	 * might otherwise copy PageMlocked to part of the tail pages before
	 * we clear it in the head page. It also stabilizes hpage_nr_pages().
	 */
	spin_lock_irq(&zone->lru_lock);

	nr_pages = hpage_nr_pages(page);
	if (!TestClearPageMlocked(page))
		goto unlock_out;

	__mod_zone_page_state(zone, NR_MLOCK, -nr_pages);

	if (__munlock_isolate_lru_page(page, true)) {
		spin_unlock_irq(&zone->lru_lock);
		__munlock_isolated_page(page);
		goto out;
	}
	__munlock_isolation_failed(page);

unlock_out:
	spin_unlock_irq(&zone->lru_lock);

out:
	return nr_pages - 1;
}

/**
 * __mlock_vma_pages_range() -  mlock a range of pages in the vma.
 * @vma:   target vma
 * @start: start address
 * @end:   end address
 * @nonblocking:
 *
 * This takes care of making the pages present too.
 *
 * return 0 on success, negative error code on error.
 *
 * vma->vm_mm->mmap_sem must be held.
 *
 * If @nonblocking is NULL, it may be held for read or write and will
 * be unperturbed.
 *
 * If @nonblocking is non-NULL, it must held for read only and may be
 * released.  If it's released, *@nonblocking will be set to 0.
 */
long __mlock_vma_pages_range(struct vm_area_struct *vma,
		unsigned long start, unsigned long end, int *nonblocking)
{
	struct mm_struct *mm = vma->vm_mm;
	unsigned long nr_pages = (end - start) / PAGE_SIZE;
	int gup_flags;

	VM_BUG_ON(start & ~PAGE_MASK);
	VM_BUG_ON(end   & ~PAGE_MASK);
	VM_BUG_ON_VMA(start < vma->vm_start, vma);
	VM_BUG_ON_VMA(end   > vma->vm_end, vma);
	VM_BUG_ON_MM(!rwsem_is_locked(&mm->mmap_sem), mm);

	gup_flags = FOLL_TOUCH | FOLL_MLOCK;
	/*
	 * We want to touch writable mappings with a write fault in order
	 * to break COW, except for shared mappings because these don't COW
	 * and we would not want to dirty them for nothing.
	 */
	if ((vma->vm_flags & (VM_WRITE | VM_SHARED)) == VM_WRITE)
		gup_flags |=<