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    mlock.c 22.03 KiB
    /*
     *	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)
    {
    	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);
    	}
    }
    
    /*
     * 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;
    
    	BUG_ON(!PageLocked(page));
    
    	if (TestClearPageMlocked(page)) {
    		nr_pages = hpage_nr_pages(page);
    		mod_zone_page_state(page_zone(page), NR_MLOCK, -nr_pages);
    		if (!isolate_lru_page(page))
    			__munlock_isolated_page(page);
    		else
    			__munlock_isolation_failed(page);
    	} else {
    		nr_pages = hpage_nr_pages(page);
    	}
    
    	/*
    	 * Regardless of the original PageMlocked flag, we determine nr_pages
    	 * after touching the flag. This leaves a possible race with a THP page
    	 * split, such that a whole THP page was munlocked, but nr_pages == 1.
    	 * Returning a smaller mask due to that is OK, the worst that can
    	 * happen is subsequent useless scanning of the former tail pages.
    	 * The NR_MLOCK accounting can however become broken.
    	 */
    	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
     *
     * 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 for at least read.
     */
    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(start < vma->vm_start);
    	VM_BUG_ON(end   > vma->vm_end);
    	VM_BUG_ON(!rwsem_is_locked(&mm->mmap_sem));
    
    	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 |= FOLL_WRITE;
    
    	/*
    	 * We want mlock to succeed for regions that have any permissions
    	 * other than PROT_NONE.
    	 */
    	if (vma->vm_flags & (VM_READ | VM_WRITE | VM_EXEC))
    		gup_flags |= FOLL_FORCE;
    
    	/*
    	 * We made sure addr is within a VMA, so the following will
    	 * not result in a stack expansion that recurses back here.
    	 */
    	return __get_user_pages(current, mm, start, nr_pages, gup_flags,
    				NULL, NULL, nonblocking);
    }
    
    /*
     * convert get_user_pages() return value to posix mlock() error
     */
    static int __mlock_posix_error_return(long retval)
    {
    	if (retval == -EFAULT)
    		retval = -ENOMEM;
    	else if (retval == -ENOMEM)
    		retval = -EAGAIN;
    	return retval;
    }
    
    /*
     * Prepare page for fast batched LRU putback via putback_lru_evictable_pagevec()
     *
     * The fast path is available only for evictable pages with single mapping.
     * Then we can bypass the per-cpu pvec and get better performance.
     * when mapcount > 1 we need try_to_munlock() which can fail.
     * when !page_evictable(), we need the full redo logic of putback_lru_page to
     * avoid leaving evictable page in unevictable list.
     *
     * In case of success, @page is added to @pvec and @pgrescued is incremented
     * in case that the page was previously unevictable. @page is also unlocked.
     */
    static bool __putback_lru_fast_prepare(struct page *page, struct pagevec *pvec,
    		int *pgrescued)
    {
    	VM_BUG_ON(PageLRU(page));
    	VM_BUG_ON(!PageLocked(page));
    
    	if (page_mapcount(page) <= 1 && page_evictable(page)) {
    		pagevec_add(pvec, page);
    		if (TestClearPageUnevictable(page))
    			(*pgrescued)++;
    		unlock_page(page);
    		return true;
    	}
    
    	return false;
    }
    
    /*
     * Putback multiple evictable pages to the LRU
     *
     * Batched putback of evictable pages that bypasses the per-cpu pvec. Some of
     * the pages might have meanwhile become unevictable but that is OK.
     */
    static void __putback_lru_fast(struct pagevec *pvec, int pgrescued)
    {
    	count_vm_events(UNEVICTABLE_PGMUNLOCKED, pagevec_count(pvec));
    	/*
    	 *__pagevec_lru_add() calls release_pages() so we don't call
    	 * put_page() explicitly
    	 */
    	__pagevec_lru_add(pvec);
    	count_vm_events(UNEVICTABLE_PGRESCUED, pgrescued);
    }
    
    /*
     * Munlock a batch of pages from the same zone
     *
     * The work is split to two main phases. First phase clears the Mlocked flag
     * and attempts to isolate the pages, all under a single zone lru lock.
     * The second phase finishes the munlock only for pages where isolation
     * succeeded.
     *
     * Note that the pagevec may be modified during the process.
     */
    static void __munlock_pagevec(struct pagevec *pvec, struct zone *zone)
    {
    	int i;
    	int nr = pagevec_count(pvec);
    	int delta_munlocked = -nr;
    	struct pagevec pvec_putback;
    	int pgrescued = 0;
    
    	/* Phase 1: page isolation */
    	spin_lock_irq(&zone->lru_lock);
    	for (i = 0; i < nr; i++) {
    		struct page *page = pvec->pages[i];
    
    		if (TestClearPageMlocked(page)) {
    			struct lruvec *lruvec;
    			int lru;
    
    			if (PageLRU(page)) {
    				lruvec = mem_cgroup_page_lruvec(page, zone);
    				lru = page_lru(page);
    				/*
    				 * We already have pin from follow_page_mask()
    				 * so we can spare the get_page() here.
    				 */
    				ClearPageLRU(page);
    				del_page_from_lru_list(page, lruvec, lru);
    			} else {
    				__munlock_isolation_failed(page);
    				goto skip_munlock;
    			}
    
    		} else {
    skip_munlock:
    			/*
    			 * We won't be munlocking this page in the next phase
    			 * but we still need to release the follow_page_mask()
    			 * pin.
    			 */
    			pvec->pages[i] = NULL;
    			put_page(page);
    			delta_munlocked++;
    		}
    	}
    	__mod_zone_page_state(zone, NR_MLOCK, delta_munlocked);
    	spin_unlock_irq(&zone->lru_lock);
    
    	/* Phase 2: page munlock */
    	pagevec_init(&pvec_putback, 0);
    	for (i = 0; i < nr; i++) {
    		struct page *page = pvec->pages[i];
    
    		if (page) {
    			lock_page(page);
    			if (!__putback_lru_fast_prepare(page, &pvec_putback,
    					&pgrescued)) {
    				/*
    				 * Slow path. We don't want to lose the last
    				 * pin before unlock_page()
    				 */
    				get_page(page); /* for putback_lru_page() */
    				__munlock_isolated_page(page);
    				unlock_page(page);
    				put_page(page); /* from follow_page_mask() */
    			}
    		}
    	}
    
    	/*
    	 * Phase 3: page putback for pages that qualified for the fast path
    	 * This will also call put_page() to return pin from follow_page_mask()
    	 */
    	if (pagevec_count(&pvec_putback))
    		__putback_lru_fast(&pvec_putback, pgrescued);
    }
    
    /*
     * Fill up pagevec for __munlock_pagevec using pte walk
     *
     * The function expects that the struct page corresponding to @start address is
     * a non-TPH page already pinned and in the @pvec, and that it belongs to @zone.
     *
     * The rest of @pvec is filled by subsequent pages within the same pmd and same
     * zone, as long as the pte's are present and vm_normal_page() succeeds. These
     * pages also get pinned.
     *
     * Returns the address of the next page that should be scanned. This equals
     * @start + PAGE_SIZE when no page could be added by the pte walk.
     */
    static unsigned long __munlock_pagevec_fill(struct pagevec *pvec,
    		struct vm_area_struct *vma, int zoneid,	unsigned long start,
    		unsigned long end)
    {
    	pte_t *pte;
    	spinlock_t *ptl;
    
    	/*
    	 * Initialize pte walk starting at the already pinned page where we
    	 * are sure that there is a pte, as it was pinned under the same
    	 * mmap_sem write op.
    	 */
    	pte = get_locked_pte(vma->vm_mm, start,	&ptl);
    	/* Make sure we do not cross the page table boundary */
    	end = pgd_addr_end(start, end);
    	end = pud_addr_end(start, end);
    	end = pmd_addr_end(start, end);
    
    	/* The page next to the pinned page is the first we will try to get */
    	start += PAGE_SIZE;
    	while (start < end) {
    		struct page *page = NULL;
    		pte++;
    		if (pte_present(*pte))
    			page = vm_normal_page(vma, start, *pte);
    		/*
    		 * Break if page could not be obtained or the page's node+zone does not
    		 * match
    		 */
    		if (!page || page_zone_id(page) != zoneid)
    			break;
    
    		get_page(page);
    		/*
    		 * Increase the address that will be returned *before* the
    		 * eventual break due to pvec becoming full by adding the page
    		 */
    		start += PAGE_SIZE;
    		if (pagevec_add(pvec, page) == 0)
    			break;
    	}
    	pte_unmap_unlock(pte, ptl);
    	return start;
    }
    
    /*
     * munlock_vma_pages_range() - munlock all pages in the vma range.'
     * @vma - vma containing range to be munlock()ed.
     * @start - start address in @vma of the range
     * @end - end of range in @vma.
     *
     *  For mremap(), munmap() and exit().
     *
     * Called with @vma VM_LOCKED.
     *
     * Returns with VM_LOCKED cleared.  Callers must be prepared to
     * deal with this.
     *
     * We don't save and restore VM_LOCKED here because pages are
     * still on lru.  In unmap path, pages might be scanned by reclaim
     * and re-mlocked by try_to_{munlock|unmap} before we unmap and
     * free them.  This will result in freeing mlocked pages.
     */
    void munlock_vma_pages_range(struct vm_area_struct *vma,
    			     unsigned long start, unsigned long end)
    {
    	vma->vm_flags &= ~VM_LOCKED;
    
    	while (start < end) {
    		struct page *page = NULL;
    		unsigned int page_mask;
    		unsigned long page_increm;
    		struct pagevec pvec;
    		struct zone *zone;
    		int zoneid;
    
    		pagevec_init(&pvec, 0);
    		/*
    		 * Although FOLL_DUMP is intended for get_dump_page(),
    		 * it just so happens that its special treatment of the
    		 * ZERO_PAGE (returning an error instead of doing get_page)
    		 * suits munlock very well (and if somehow an abnormal page
    		 * has sneaked into the range, we won't oops here: great).
    		 */
    		page = follow_page_mask(vma, start, FOLL_GET | FOLL_DUMP,
    				&page_mask);
    
    		if (page && !IS_ERR(page)) {
    			if (PageTransHuge(page)) {
    				lock_page(page);
    				/*
    				 * Any THP page found by follow_page_mask() may
    				 * have gotten split before reaching
    				 * munlock_vma_page(), so we need to recompute
    				 * the page_mask here.
    				 */
    				page_mask = munlock_vma_page(page);
    				unlock_page(page);
    				put_page(page); /* follow_page_mask() */
    			} else {
    				/*
    				 * Non-huge pages are handled in batches via
    				 * pagevec. The pin from follow_page_mask()
    				 * prevents them from collapsing by THP.
    				 */
    				pagevec_add(&pvec, page);
    				zone = page_zone(page);
    				zoneid = page_zone_id(page);
    
    				/*
    				 * Try to fill the rest of pagevec using fast
    				 * pte walk. This will also update start to
    				 * the next page to process. Then munlock the
    				 * pagevec.
    				 */
    				start = __munlock_pagevec_fill(&pvec, vma,
    						zoneid, start, end);
    				__munlock_pagevec(&pvec, zone);
    				goto next;
    			}
    		}
    		/* It's a bug to munlock in the middle of a THP page */
    		VM_BUG_ON((start >> PAGE_SHIFT) & page_mask);
    		page_increm = 1 + page_mask;
    		start += page_increm * PAGE_SIZE;
    next:
    		cond_resched();
    	}
    }
    
    /*
     * mlock_fixup  - handle mlock[all]/munlock[all] requests.
     *
     * Filters out "special" vmas -- VM_LOCKED never gets set for these, and
     * munlock is a no-op.  However, for some special vmas, we go ahead and
     * populate the ptes.
     *
     * For vmas that pass the filters, merge/split as appropriate.
     */
    static int mlock_fixup(struct vm_area_struct *vma, struct vm_area_struct **prev,
    	unsigned long start, unsigned long end, vm_flags_t newflags)
    {
    	struct mm_struct *mm = vma->vm_mm;
    	pgoff_t pgoff;
    	int nr_pages;
    	int ret = 0;
    	int lock = !!(newflags & VM_LOCKED);
    
    	if (newflags == vma->vm_flags || (vma->vm_flags & VM_SPECIAL) ||
    	    is_vm_hugetlb_page(vma) || vma == get_gate_vma(current->mm))
    		goto out;	/* don't set VM_LOCKED,  don't count */
    
    	pgoff = vma->vm_pgoff + ((start - vma->vm_start) >> PAGE_SHIFT);
    	*prev = vma_merge(mm, *prev, start, end, newflags, vma->anon_vma,
    			  vma->vm_file, pgoff, vma_policy(vma));
    	if (*prev) {
    		vma = *prev;
    		goto success;
    	}
    
    	if (start != vma->vm_start) {
    		ret = split_vma(mm, vma, start, 1);
    		if (ret)
    			goto out;
    	}
    
    	if (end != vma->vm_end) {
    		ret = split_vma(mm, vma, end, 0);
    		if (ret)
    			goto out;
    	}
    
    success:
    	/*
    	 * Keep track of amount of locked VM.
    	 */
    	nr_pages = (end - start) >> PAGE_SHIFT;
    	if (!lock)
    		nr_pages = -nr_pages;
    	mm->locked_vm += nr_pages;
    
    	/*
    	 * vm_flags is protected by the mmap_sem held in write mode.
    	 * It's okay if try_to_unmap_one unmaps a page just after we
    	 * set VM_LOCKED, __mlock_vma_pages_range will bring it back.
    	 */
    
    	if (lock)
    		vma->vm_flags = newflags;
    	else
    		munlock_vma_pages_range(vma, start, end);
    
    out:
    	*prev = vma;
    	return ret;
    }
    
    static int do_mlock(unsigned long start, size_t len, int on)
    {
    	unsigned long nstart, end, tmp;
    	struct vm_area_struct * vma, * prev;
    	int error;
    
    	VM_BUG_ON(start & ~PAGE_MASK);
    	VM_BUG_ON(len != PAGE_ALIGN(len));
    	end = start + len;
    	if (end < start)
    		return -EINVAL;
    	if (end == start)
    		return 0;
    	vma = find_vma(current->mm, start);
    	if (!vma || vma->vm_start > start)
    		return -ENOMEM;
    
    	prev = vma->vm_prev;
    	if (start > vma->vm_start)
    		prev = vma;
    
    	for (nstart = start ; ; ) {
    		vm_flags_t newflags;
    
    		/* Here we know that  vma->vm_start <= nstart < vma->vm_end. */
    
    		newflags = vma->vm_flags & ~VM_LOCKED;
    		if (on)
    			newflags |= VM_LOCKED;
    
    		tmp = vma->vm_end;
    		if (tmp > end)
    			tmp = end;
    		error = mlock_fixup(vma, &prev, nstart, tmp, newflags);
    		if (error)
    			break;
    		nstart = tmp;
    		if (nstart < prev->vm_end)
    			nstart = prev->vm_end;
    		if (nstart >= end)
    			break;
    
    		vma = prev->vm_next;
    		if (!vma || vma->vm_start != nstart) {
    			error = -ENOMEM;
    			break;
    		}
    	}
    	return error;
    }
    
    /*
     * __mm_populate - populate and/or mlock pages within a range of address space.
     *
     * This is used to implement mlock() and the MAP_POPULATE / MAP_LOCKED mmap
     * flags. VMAs must be already marked with the desired vm_flags, and
     * mmap_sem must not be held.
     */
    int __mm_populate(unsigned long start, unsigned long len, int ignore_errors)
    {
    	struct mm_struct *mm = current->mm;
    	unsigned long end, nstart, nend;
    	struct vm_area_struct *vma = NULL;
    	int locked = 0;
    	long ret = 0;
    
    	VM_BUG_ON(start & ~PAGE_MASK);
    	VM_BUG_ON(len != PAGE_ALIGN(len));
    	end = start + len;
    
    	for (nstart = start; nstart < end; nstart = nend) {
    		/*
    		 * We want to fault in pages for [nstart; end) address range.
    		 * Find first corresponding VMA.
    		 */
    		if (!locked) {
    			locked = 1;
    			down_read(&mm->mmap_sem);
    			vma = find_vma(mm, nstart);
    		} else if (nstart >= vma->vm_end)
    			vma = vma->vm_next;
    		if (!vma || vma->vm_start >= end)
    			break;
    		/*
    		 * Set [nstart; nend) to intersection of desired address
    		 * range with the first VMA. Also, skip undesirable VMA types.
    		 */
    		nend = min(end, vma->vm_end);
    		if (vma->vm_flags & (VM_IO | VM_PFNMAP))
    			continue;
    		if (nstart < vma->vm_start)
    			nstart = vma->vm_start;
    		/*
    		 * Now fault in a range of pages. __mlock_vma_pages_range()
    		 * double checks the vma flags, so that it won't mlock pages
    		 * if the vma was already munlocked.
    		 */
    		ret = __mlock_vma_pages_range(vma, nstart, nend, &locked);
    		if (ret < 0) {
    			if (ignore_errors) {
    				ret = 0;
    				continue;	/* continue at next VMA */
    			}
    			ret = __mlock_posix_error_return(ret);
    			break;
    		}
    		nend = nstart + ret * PAGE_SIZE;
    		ret = 0;
    	}
    	if (locked)
    		up_read(&mm->mmap_sem);
    	return ret;	/* 0 or negative error code */
    }
    
    SYSCALL_DEFINE2(mlock, unsigned long, start, size_t, len)
    {
    	unsigned long locked;
    	unsigned long lock_limit;
    	int error = -ENOMEM;
    
    	if (!can_do_mlock())
    		return -EPERM;
    
    	lru_add_drain_all();	/* flush pagevec */
    
    	down_write(&current->mm->mmap_sem);
    	len = PAGE_ALIGN(len + (start & ~PAGE_MASK));
    	start &= PAGE_MASK;
    
    	locked = len >> PAGE_SHIFT;
    	locked += current->mm->locked_vm;
    
    	lock_limit = rlimit(RLIMIT_MEMLOCK);
    	lock_limit >>= PAGE_SHIFT;
    
    	/* check against resource limits */
    	if ((locked <= lock_limit) || capable(CAP_IPC_LOCK))
    		error = do_mlock(start, len, 1);
    	up_write(&current->mm->mmap_sem);
    	if (!error)
    		error = __mm_populate(start, len, 0);
    	return error;
    }
    
    SYSCALL_DEFINE2(munlock, unsigned long, start, size_t, len)
    {
    	int ret;
    
    	down_write(&current->mm->mmap_sem);
    	len = PAGE_ALIGN(len + (start & ~PAGE_MASK));
    	start &= PAGE_MASK;
    	ret = do_mlock(start, len, 0);
    	up_write(&current->mm->mmap_sem);
    	return ret;
    }
    
    static int do_mlockall(int flags)
    {
    	struct vm_area_struct * vma, * prev = NULL;
    
    	if (flags & MCL_FUTURE)
    		current->mm->def_flags |= VM_LOCKED;
    	else
    		current->mm->def_flags &= ~VM_LOCKED;
    	if (flags == MCL_FUTURE)
    		goto out;
    
    	for (vma = current->mm->mmap; vma ; vma = prev->vm_next) {
    		vm_flags_t newflags;
    
    		newflags = vma->vm_flags & ~VM_LOCKED;
    		if (flags & MCL_CURRENT)
    			newflags |= VM_LOCKED;
    
    		/* Ignore errors */
    		mlock_fixup(vma, &prev, vma->vm_start, vma->vm_end, newflags);
    		cond_resched();
    	}
    out:
    	return 0;
    }
    
    SYSCALL_DEFINE1(mlockall, int, flags)
    {
    	unsigned long lock_limit;
    	int ret = -EINVAL;
    
    	if (!flags || (flags & ~(MCL_CURRENT | MCL_FUTURE)))
    		goto out;
    
    	ret = -EPERM;
    	if (!can_do_mlock())
    		goto out;
    
    	if (flags & MCL_CURRENT)
    		lru_add_drain_all();	/* flush pagevec */
    
    	down_write(&current->mm->mmap_sem);
    
    	lock_limit = rlimit(RLIMIT_MEMLOCK);
    	lock_limit >>= PAGE_SHIFT;
    
    	ret = -ENOMEM;
    	if (!(flags & MCL_CURRENT) || (current->mm->total_vm <= lock_limit) ||
    	    capable(CAP_IPC_LOCK))
    		ret = do_mlockall(flags);
    	up_write(&current->mm->mmap_sem);
    	if (!ret && (flags & MCL_CURRENT))
    		mm_populate(0, TASK_SIZE);
    out:
    	return ret;
    }
    
    SYSCALL_DEFINE0(munlockall)
    {
    	int ret;
    
    	down_write(&current->mm->mmap_sem);
    	ret = do_mlockall(0);
    	up_write(&current->mm->mmap_sem);
    	return ret;
    }
    
    /*
     * Objects with different lifetime than processes (SHM_LOCK and SHM_HUGETLB
     * shm segments) get accounted against the user_struct instead.
     */
    static DEFINE_SPINLOCK(shmlock_user_lock);
    
    int user_shm_lock(size_t size, struct user_struct *user)
    {
    	unsigned long lock_limit, locked;
    	int allowed = 0;
    
    	locked = (size + PAGE_SIZE - 1) >> PAGE_SHIFT;
    	lock_limit = rlimit(RLIMIT_MEMLOCK);
    	if (lock_limit == RLIM_INFINITY)
    		allowed = 1;
    	lock_limit >>= PAGE_SHIFT;
    	spin_lock(&shmlock_user_lock);
    	if (!allowed &&
    	    locked + user->locked_shm > lock_limit && !capable(CAP_IPC_LOCK))
    		goto out;
    	get_uid(user);
    	user->locked_shm += locked;
    	allowed = 1;
    out:
    	spin_unlock(&shmlock_user_lock);
    	return allowed;
    }
    
    void user_shm_unlock(size_t size, struct user_struct *user)
    {
    	spin_lock(&shmlock_user_lock);
    	user->locked_shm -= (size + PAGE_SIZE - 1) >> PAGE_SHIFT;
    	spin_unlock(&shmlock_user_lock);
    	free_uid(user);
    }