shmem.c 63.8 KB
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/*
 * Resizable virtual memory filesystem for Linux.
 *
 * Copyright (C) 2000 Linus Torvalds.
 *		 2000 Transmeta Corp.
 *		 2000-2001 Christoph Rohland
 *		 2000-2001 SAP AG
 *		 2002 Red Hat Inc.
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 * Copyright (C) 2002-2011 Hugh Dickins.
 * Copyright (C) 2011 Google Inc.
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 * Copyright (C) 2002-2005 VERITAS Software Corporation.
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 * Copyright (C) 2004 Andi Kleen, SuSE Labs
 *
 * Extended attribute support for tmpfs:
 * Copyright (c) 2004, Luke Kenneth Casson Leighton <lkcl@lkcl.net>
 * Copyright (c) 2004 Red Hat, Inc., James Morris <jmorris@redhat.com>
 *
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 * tiny-shmem:
 * Copyright (c) 2004, 2008 Matt Mackall <mpm@selenic.com>
 *
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 * This file is released under the GPL.
 */

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#include <linux/fs.h>
#include <linux/init.h>
#include <linux/vfs.h>
#include <linux/mount.h>
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#include <linux/pagemap.h>
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#include <linux/file.h>
#include <linux/mm.h>
#include <linux/module.h>
#include <linux/swap.h>

static struct vfsmount *shm_mnt;

#ifdef CONFIG_SHMEM
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/*
 * This virtual memory filesystem is heavily based on the ramfs. It
 * extends ramfs by the ability to use swap and honor resource limits
 * which makes it a completely usable filesystem.
 */

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#include <linux/xattr.h>
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#include <linux/exportfs.h>
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#include <linux/posix_acl.h>
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#include <linux/generic_acl.h>
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#include <linux/mman.h>
#include <linux/string.h>
#include <linux/slab.h>
#include <linux/backing-dev.h>
#include <linux/shmem_fs.h>
#include <linux/writeback.h>
#include <linux/blkdev.h>
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#include <linux/pagevec.h>
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#include <linux/percpu_counter.h>
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#include <linux/splice.h>
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#include <linux/security.h>
#include <linux/swapops.h>
#include <linux/mempolicy.h>
#include <linux/namei.h>
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#include <linux/ctype.h>
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#include <linux/migrate.h>
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#include <linux/highmem.h>
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#include <linux/seq_file.h>
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#include <linux/magic.h>
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#include <asm/uaccess.h>
#include <asm/pgtable.h>

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#define BLOCKS_PER_PAGE  (PAGE_CACHE_SIZE/512)
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#define VM_ACCT(size)    (PAGE_CACHE_ALIGN(size) >> PAGE_SHIFT)

/* Pretend that each entry is of this size in directory's i_size */
#define BOGO_DIRENT_SIZE 20

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/* Symlink up to this size is kmalloc'ed instead of using a swappable page */
#define SHORT_SYMLINK_LEN 128

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struct shmem_xattr {
	struct list_head list;	/* anchored by shmem_inode_info->xattr_list */
	char *name;		/* xattr name */
	size_t size;
	char value[0];
};

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/* Flag allocation requirements to shmem_getpage */
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enum sgp_type {
	SGP_READ,	/* don't exceed i_size, don't allocate page */
	SGP_CACHE,	/* don't exceed i_size, may allocate page */
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	SGP_DIRTY,	/* like SGP_CACHE, but set new page dirty */
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	SGP_WRITE,	/* may exceed i_size, may allocate page */
};

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#ifdef CONFIG_TMPFS
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static unsigned long shmem_default_max_blocks(void)
{
	return totalram_pages / 2;
}

static unsigned long shmem_default_max_inodes(void)
{
	return min(totalram_pages - totalhigh_pages, totalram_pages / 2);
}
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#endif
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static int shmem_getpage_gfp(struct inode *inode, pgoff_t index,
	struct page **pagep, enum sgp_type sgp, gfp_t gfp, int *fault_type);

static inline int shmem_getpage(struct inode *inode, pgoff_t index,
	struct page **pagep, enum sgp_type sgp, int *fault_type)
{
	return shmem_getpage_gfp(inode, index, pagep, sgp,
			mapping_gfp_mask(inode->i_mapping), fault_type);
}
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static inline struct shmem_sb_info *SHMEM_SB(struct super_block *sb)
{
	return sb->s_fs_info;
}

/*
 * shmem_file_setup pre-accounts the whole fixed size of a VM object,
 * for shared memory and for shared anonymous (/dev/zero) mappings
 * (unless MAP_NORESERVE and sysctl_overcommit_memory <= 1),
 * consistent with the pre-accounting of private mappings ...
 */
static inline int shmem_acct_size(unsigned long flags, loff_t size)
{
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	return (flags & VM_NORESERVE) ?
		0 : security_vm_enough_memory_kern(VM_ACCT(size));
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}

static inline void shmem_unacct_size(unsigned long flags, loff_t size)
{
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	if (!(flags & VM_NORESERVE))
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		vm_unacct_memory(VM_ACCT(size));
}

/*
 * ... whereas tmpfs objects are accounted incrementally as
 * pages are allocated, in order to allow huge sparse files.
 * shmem_getpage reports shmem_acct_block failure as -ENOSPC not -ENOMEM,
 * so that a failure on a sparse tmpfs mapping will give SIGBUS not OOM.
 */
static inline int shmem_acct_block(unsigned long flags)
{
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	return (flags & VM_NORESERVE) ?
		security_vm_enough_memory_kern(VM_ACCT(PAGE_CACHE_SIZE)) : 0;
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}

static inline void shmem_unacct_blocks(unsigned long flags, long pages)
{
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	if (flags & VM_NORESERVE)
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		vm_unacct_memory(pages * VM_ACCT(PAGE_CACHE_SIZE));
}

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static const struct super_operations shmem_ops;
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static const struct address_space_operations shmem_aops;
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static const struct file_operations shmem_file_operations;
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static const struct inode_operations shmem_inode_operations;
static const struct inode_operations shmem_dir_inode_operations;
static const struct inode_operations shmem_special_inode_operations;
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static const struct vm_operations_struct shmem_vm_ops;
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static struct backing_dev_info shmem_backing_dev_info  __read_mostly = {
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	.ra_pages	= 0,	/* No readahead */
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	.capabilities	= BDI_CAP_NO_ACCT_AND_WRITEBACK | BDI_CAP_SWAP_BACKED,
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};

static LIST_HEAD(shmem_swaplist);
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static DEFINE_MUTEX(shmem_swaplist_mutex);
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static int shmem_reserve_inode(struct super_block *sb)
{
	struct shmem_sb_info *sbinfo = SHMEM_SB(sb);
	if (sbinfo->max_inodes) {
		spin_lock(&sbinfo->stat_lock);
		if (!sbinfo->free_inodes) {
			spin_unlock(&sbinfo->stat_lock);
			return -ENOSPC;
		}
		sbinfo->free_inodes--;
		spin_unlock(&sbinfo->stat_lock);
	}
	return 0;
}

static void shmem_free_inode(struct super_block *sb)
{
	struct shmem_sb_info *sbinfo = SHMEM_SB(sb);
	if (sbinfo->max_inodes) {
		spin_lock(&sbinfo->stat_lock);
		sbinfo->free_inodes++;
		spin_unlock(&sbinfo->stat_lock);
	}
}

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/**
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 * shmem_recalc_inode - recalculate the block usage of an inode
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 * @inode: inode to recalc
 *
 * We have to calculate the free blocks since the mm can drop
 * undirtied hole pages behind our back.
 *
 * But normally   info->alloced == inode->i_mapping->nrpages + info->swapped
 * So mm freed is info->alloced - (inode->i_mapping->nrpages + info->swapped)
 *
 * It has to be called with the spinlock held.
 */
static void shmem_recalc_inode(struct inode *inode)
{
	struct shmem_inode_info *info = SHMEM_I(inode);
	long freed;

	freed = info->alloced - info->swapped - inode->i_mapping->nrpages;
	if (freed > 0) {
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		struct shmem_sb_info *sbinfo = SHMEM_SB(inode->i_sb);
		if (sbinfo->max_blocks)
			percpu_counter_add(&sbinfo->used_blocks, -freed);
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		info->alloced -= freed;
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		inode->i_blocks -= freed * BLOCKS_PER_PAGE;
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		shmem_unacct_blocks(info->flags, freed);
	}
}

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/*
 * Replace item expected in radix tree by a new item, while holding tree lock.
 */
static int shmem_radix_tree_replace(struct address_space *mapping,
			pgoff_t index, void *expected, void *replacement)
{
	void **pslot;
	void *item = NULL;

	VM_BUG_ON(!expected);
	pslot = radix_tree_lookup_slot(&mapping->page_tree, index);
	if (pslot)
		item = radix_tree_deref_slot_protected(pslot,
							&mapping->tree_lock);
	if (item != expected)
		return -ENOENT;
	if (replacement)
		radix_tree_replace_slot(pslot, replacement);
	else
		radix_tree_delete(&mapping->page_tree, index);
	return 0;
}

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/*
 * Like add_to_page_cache_locked, but error if expected item has gone.
 */
static int shmem_add_to_page_cache(struct page *page,
				   struct address_space *mapping,
				   pgoff_t index, gfp_t gfp, void *expected)
{
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	int error = 0;
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	VM_BUG_ON(!PageLocked(page));
	VM_BUG_ON(!PageSwapBacked(page));

	if (!expected)
		error = radix_tree_preload(gfp & GFP_RECLAIM_MASK);
	if (!error) {
		page_cache_get(page);
		page->mapping = mapping;
		page->index = index;

		spin_lock_irq(&mapping->tree_lock);
		if (!expected)
			error = radix_tree_insert(&mapping->page_tree,
							index, page);
		else
			error = shmem_radix_tree_replace(mapping, index,
							expected, page);
		if (!error) {
			mapping->nrpages++;
			__inc_zone_page_state(page, NR_FILE_PAGES);
			__inc_zone_page_state(page, NR_SHMEM);
			spin_unlock_irq(&mapping->tree_lock);
		} else {
			page->mapping = NULL;
			spin_unlock_irq(&mapping->tree_lock);
			page_cache_release(page);
		}
		if (!expected)
			radix_tree_preload_end();
	}
	if (error)
		mem_cgroup_uncharge_cache_page(page);
	return error;
}

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/*
 * Like delete_from_page_cache, but substitutes swap for page.
 */
static void shmem_delete_from_page_cache(struct page *page, void *radswap)
{
	struct address_space *mapping = page->mapping;
	int error;

	spin_lock_irq(&mapping->tree_lock);
	error = shmem_radix_tree_replace(mapping, page->index, page, radswap);
	page->mapping = NULL;
	mapping->nrpages--;
	__dec_zone_page_state(page, NR_FILE_PAGES);
	__dec_zone_page_state(page, NR_SHMEM);
	spin_unlock_irq(&mapping->tree_lock);
	page_cache_release(page);
	BUG_ON(error);
}

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/*
 * Like find_get_pages, but collecting swap entries as well as pages.
 */
static unsigned shmem_find_get_pages_and_swap(struct address_space *mapping,
					pgoff_t start, unsigned int nr_pages,
					struct page **pages, pgoff_t *indices)
{
	unsigned int i;
	unsigned int ret;
	unsigned int nr_found;

	rcu_read_lock();
restart:
	nr_found = radix_tree_gang_lookup_slot(&mapping->page_tree,
				(void ***)pages, indices, start, nr_pages);
	ret = 0;
	for (i = 0; i < nr_found; i++) {
		struct page *page;
repeat:
		page = radix_tree_deref_slot((void **)pages[i]);
		if (unlikely(!page))
			continue;
		if (radix_tree_exception(page)) {
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			if (radix_tree_deref_retry(page))
				goto restart;
			/*
			 * Otherwise, we must be storing a swap entry
			 * here as an exceptional entry: so return it
			 * without attempting to raise page count.
			 */
			goto export;
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		}
		if (!page_cache_get_speculative(page))
			goto repeat;

		/* Has the page moved? */
		if (unlikely(page != *((void **)pages[i]))) {
			page_cache_release(page);
			goto repeat;
		}
export:
		indices[ret] = indices[i];
		pages[ret] = page;
		ret++;
	}
	if (unlikely(!ret && nr_found))
		goto restart;
	rcu_read_unlock();
	return ret;
}

/*
 * Remove swap entry from radix tree, free the swap and its page cache.
 */
static int shmem_free_swap(struct address_space *mapping,
			   pgoff_t index, void *radswap)
{
	int error;

	spin_lock_irq(&mapping->tree_lock);
	error = shmem_radix_tree_replace(mapping, index, radswap, NULL);
	spin_unlock_irq(&mapping->tree_lock);
	if (!error)
		free_swap_and_cache(radix_to_swp_entry(radswap));
	return error;
}

/*
 * Pagevec may contain swap entries, so shuffle up pages before releasing.
 */
static void shmem_pagevec_release(struct pagevec *pvec)
{
	int i, j;

	for (i = 0, j = 0; i < pagevec_count(pvec); i++) {
		struct page *page = pvec->pages[i];
		if (!radix_tree_exceptional_entry(page))
			pvec->pages[j++] = page;
	}
	pvec->nr = j;
	pagevec_release(pvec);
}

/*
 * Remove range of pages and swap entries from radix tree, and free them.
 */
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void shmem_truncate_range(struct inode *inode, loff_t lstart, loff_t lend)
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{
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	struct address_space *mapping = inode->i_mapping;
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	struct shmem_inode_info *info = SHMEM_I(inode);
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	pgoff_t start = (lstart + PAGE_CACHE_SIZE - 1) >> PAGE_CACHE_SHIFT;
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	unsigned partial = lstart & (PAGE_CACHE_SIZE - 1);
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	pgoff_t end = (lend >> PAGE_CACHE_SHIFT);
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	struct pagevec pvec;
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	pgoff_t indices[PAGEVEC_SIZE];
	long nr_swaps_freed = 0;
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	pgoff_t index;
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	int i;

	BUG_ON((lend & (PAGE_CACHE_SIZE - 1)) != (PAGE_CACHE_SIZE - 1));

	pagevec_init(&pvec, 0);
	index = start;
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	while (index <= end) {
		pvec.nr = shmem_find_get_pages_and_swap(mapping, index,
			min(end - index, (pgoff_t)PAGEVEC_SIZE - 1) + 1,
							pvec.pages, indices);
		if (!pvec.nr)
			break;
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		mem_cgroup_uncharge_start();
		for (i = 0; i < pagevec_count(&pvec); i++) {
			struct page *page = pvec.pages[i];

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			index = indices[i];
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			if (index > end)
				break;

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			if (radix_tree_exceptional_entry(page)) {
				nr_swaps_freed += !shmem_free_swap(mapping,
								index, page);
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				continue;
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			}

			if (!trylock_page(page))
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				continue;
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			if (page->mapping == mapping) {
				VM_BUG_ON(PageWriteback(page));
				truncate_inode_page(mapping, page);
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			}
			unlock_page(page);
		}
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		shmem_pagevec_release(&pvec);
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		mem_cgroup_uncharge_end();
		cond_resched();
		index++;
	}
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	if (partial) {
		struct page *page = NULL;
		shmem_getpage(inode, start - 1, &page, SGP_READ, NULL);
		if (page) {
			zero_user_segment(page, partial, PAGE_CACHE_SIZE);
			set_page_dirty(page);
			unlock_page(page);
			page_cache_release(page);
		}
	}

	index = start;
	for ( ; ; ) {
		cond_resched();
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		pvec.nr = shmem_find_get_pages_and_swap(mapping, index,
			min(end - index, (pgoff_t)PAGEVEC_SIZE - 1) + 1,
							pvec.pages, indices);
		if (!pvec.nr) {
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			if (index == start)
				break;
			index = start;
			continue;
		}
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		if (index == start && indices[0] > end) {
			shmem_pagevec_release(&pvec);
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			break;
		}
		mem_cgroup_uncharge_start();
		for (i = 0; i < pagevec_count(&pvec); i++) {
			struct page *page = pvec.pages[i];

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			index = indices[i];
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			if (index > end)
				break;

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			if (radix_tree_exceptional_entry(page)) {
				nr_swaps_freed += !shmem_free_swap(mapping,
								index, page);
				continue;
			}

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			lock_page(page);
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			if (page->mapping == mapping) {
				VM_BUG_ON(PageWriteback(page));
				truncate_inode_page(mapping, page);
			}
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			unlock_page(page);
		}
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		shmem_pagevec_release(&pvec);
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		mem_cgroup_uncharge_end();
		index++;
	}
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	spin_lock(&info->lock);
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	info->swapped -= nr_swaps_freed;
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	shmem_recalc_inode(inode);
	spin_unlock(&info->lock);

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	inode->i_ctime = inode->i_mtime = CURRENT_TIME;
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}
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EXPORT_SYMBOL_GPL(shmem_truncate_range);
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static int shmem_setattr(struct dentry *dentry, struct iattr *attr)
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{
	struct inode *inode = dentry->d_inode;
	int error;

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	error = inode_change_ok(inode, attr);
	if (error)
		return error;

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	if (S_ISREG(inode->i_mode) && (attr->ia_valid & ATTR_SIZE)) {
		loff_t oldsize = inode->i_size;
		loff_t newsize = attr->ia_size;
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		if (newsize != oldsize) {
			i_size_write(inode, newsize);
			inode->i_ctime = inode->i_mtime = CURRENT_TIME;
		}
		if (newsize < oldsize) {
			loff_t holebegin = round_up(newsize, PAGE_SIZE);
			unmap_mapping_range(inode->i_mapping, holebegin, 0, 1);
			shmem_truncate_range(inode, newsize, (loff_t)-1);
			/* unmap again to remove racily COWed private pages */
			unmap_mapping_range(inode->i_mapping, holebegin, 0, 1);
		}
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	}

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	setattr_copy(inode, attr);
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#ifdef CONFIG_TMPFS_POSIX_ACL
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	if (attr->ia_valid & ATTR_MODE)
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		error = generic_acl_chmod(inode);
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#endif
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	return error;
}

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static void shmem_evict_inode(struct inode *inode)
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{
	struct shmem_inode_info *info = SHMEM_I(inode);
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	struct shmem_xattr *xattr, *nxattr;
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	if (inode->i_mapping->a_ops == &shmem_aops) {
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		shmem_unacct_size(info->flags, inode->i_size);
		inode->i_size = 0;
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		shmem_truncate_range(inode, 0, (loff_t)-1);
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		if (!list_empty(&info->swaplist)) {
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			mutex_lock(&shmem_swaplist_mutex);
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			list_del_init(&info->swaplist);
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			mutex_unlock(&shmem_swaplist_mutex);
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		}
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	} else
		kfree(info->symlink);
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	list_for_each_entry_safe(xattr, nxattr, &info->xattr_list, list) {
		kfree(xattr->name);
		kfree(xattr);
	}
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	BUG_ON(inode->i_blocks);
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	shmem_free_inode(inode->i_sb);
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	end_writeback(inode);
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}

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/*
 * If swap found in inode, free it and move page from swapcache to filecache.
 */
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static int shmem_unuse_inode(struct shmem_inode_info *info,
			     swp_entry_t swap, struct page *page)
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{
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	struct address_space *mapping = info->vfs_inode.i_mapping;
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	void *radswap;
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	pgoff_t index;
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	int error;
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	radswap = swp_to_radix_entry(swap);
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	index = radix_tree_locate_item(&mapping->page_tree, radswap);
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	if (index == -1)
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		return 0;
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	/*
	 * Move _head_ to start search for next from here.
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	 * But be careful: shmem_evict_inode checks list_empty without taking
590
	 * mutex, and there's an instant in list_move_tail when info->swaplist
591
	 * would appear empty, if it were the only one on shmem_swaplist.
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	 */
	if (shmem_swaplist.next != &info->swaplist)
		list_move_tail(&shmem_swaplist, &info->swaplist);
595

596
	/*
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	 * We rely on shmem_swaplist_mutex, not only to protect the swaplist,
	 * but also to hold up shmem_evict_inode(): so inode cannot be freed
	 * beneath us (pagelock doesn't help until the page is in pagecache).
600
	 */
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	error = shmem_add_to_page_cache(page, mapping, index,
						GFP_NOWAIT, radswap);
603
	/* which does mem_cgroup_uncharge_cache_page on error */
604

605
	if (error != -ENOMEM) {
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		/*
		 * Truncation and eviction use free_swap_and_cache(), which
		 * only does trylock page: if we raced, best clean up here.
		 */
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		delete_from_swap_cache(page);
		set_page_dirty(page);
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		if (!error) {
			spin_lock(&info->lock);
			info->swapped--;
			spin_unlock(&info->lock);
			swap_free(swap);
		}
618
		error = 1;	/* not an error, but entry was found */
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	}
620
	return error;
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}

/*
624
 * Search through swapped inodes to find and replace swap by page.
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 */
626
int shmem_unuse(swp_entry_t swap, struct page *page)
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{
628
	struct list_head *this, *next;
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	struct shmem_inode_info *info;
	int found = 0;
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	int error;

	/*
	 * Charge page using GFP_KERNEL while we can wait, before taking
	 * the shmem_swaplist_mutex which might hold up shmem_writepage().
	 * Charged back to the user (not to caller) when swap account is used.
	 */
	error = mem_cgroup_cache_charge(page, current->mm, GFP_KERNEL);
	if (error)
		goto out;
641
	/* No radix_tree_preload: swap entry keeps a place for page in tree */
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643
	mutex_lock(&shmem_swaplist_mutex);
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	list_for_each_safe(this, next, &shmem_swaplist) {
		info = list_entry(this, struct shmem_inode_info, swaplist);
646
		if (info->swapped)
647
			found = shmem_unuse_inode(info, swap, page);
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		else
			list_del_init(&info->swaplist);
650
		cond_resched();
651
		if (found)
652
			break;
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	}
654
	mutex_unlock(&shmem_swaplist_mutex);
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	if (!found)
		mem_cgroup_uncharge_cache_page(page);
	if (found < 0)
		error = found;
out:
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	unlock_page(page);
	page_cache_release(page);
663
	return error;
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}

/*
 * Move the page from the page cache to the swap cache.
 */
static int shmem_writepage(struct page *page, struct writeback_control *wbc)
{
	struct shmem_inode_info *info;
	struct address_space *mapping;
	struct inode *inode;
674 675
	swp_entry_t swap;
	pgoff_t index;
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	BUG_ON(!PageLocked(page));
	mapping = page->mapping;
	index = page->index;
	inode = mapping->host;
	info = SHMEM_I(inode);
	if (info->flags & VM_LOCKED)
		goto redirty;
684
	if (!total_swap_pages)
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		goto redirty;

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	/*
	 * shmem_backing_dev_info's capabilities prevent regular writeback or
	 * sync from ever calling shmem_writepage; but a stacking filesystem
690
	 * might use ->writepage of its underlying filesystem, in which case
691
	 * tmpfs should write out to swap only in response to memory pressure,
692
	 * and not for the writeback threads or sync.
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	 */
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	if (!wbc->for_reclaim) {
		WARN_ON_ONCE(1);	/* Still happens? Tell us about it! */
		goto redirty;
	}
	swap = get_swap_page();
	if (!swap.val)
		goto redirty;
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	/*
	 * Add inode to shmem_unuse()'s list of swapped-out inodes,
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	 * if it's not already there.  Do it now before the page is
	 * moved to swap cache, when its pagelock no longer protects
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	 * the inode from eviction.  But don't unlock the mutex until
707 708
	 * we've incremented swapped, because shmem_unuse_inode() will
	 * prune a !swapped inode from the swaplist under this mutex.
709
	 */
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	mutex_lock(&shmem_swaplist_mutex);
	if (list_empty(&info->swaplist))
		list_add_tail(&info->swaplist, &shmem_swaplist);
713

714
	if (add_to_swap_cache(page, swap, GFP_ATOMIC) == 0) {
715
		swap_shmem_alloc(swap);
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		shmem_delete_from_page_cache(page, swp_to_radix_entry(swap));

		spin_lock(&info->lock);
		info->swapped++;
		shmem_recalc_inode(inode);
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		spin_unlock(&info->lock);
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		mutex_unlock(&shmem_swaplist_mutex);
724
		BUG_ON(page_mapped(page));
725
		swap_writepage(page, wbc);
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		return 0;
	}

729
	mutex_unlock(&shmem_swaplist_mutex);
730
	swapcache_free(swap, NULL);
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redirty:
	set_page_dirty(page);
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	if (wbc->for_reclaim)
		return AOP_WRITEPAGE_ACTIVATE;	/* Return with page locked */
	unlock_page(page);
	return 0;
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}

#ifdef CONFIG_NUMA
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#ifdef CONFIG_TMPFS
741
static void shmem_show_mpol(struct seq_file *seq, struct mempolicy *mpol)
742
{
743
	char buffer[64];
744

745
	if (!mpol || mpol->mode == MPOL_DEFAULT)
746
		return;		/* show nothing */
747

748
	mpol_to_str(buffer, sizeof(buffer), mpol, 1);
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	seq_printf(seq, ",mpol=%s", buffer);
751
}
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static struct mempolicy *shmem_get_sbmpol(struct shmem_sb_info *sbinfo)
{
	struct mempolicy *mpol = NULL;
	if (sbinfo->mpol) {
		spin_lock(&sbinfo->stat_lock);	/* prevent replace/use races */
		mpol = sbinfo->mpol;
		mpol_get(mpol);
		spin_unlock(&sbinfo->stat_lock);
	}
	return mpol;
}
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#endif /* CONFIG_TMPFS */

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static struct page *shmem_swapin(swp_entry_t swap, gfp_t gfp,
			struct shmem_inode_info *info, pgoff_t index)
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{
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	struct mempolicy mpol, *spol;
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	struct vm_area_struct pvma;

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	spol = mpol_cond_copy(&mpol,
773
			mpol_shared_policy_lookup(&info->policy, index));
774

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	/* Create a pseudo vma that just contains the policy */
776
	pvma.vm_start = 0;
777
	pvma.vm_pgoff = index;
778
	pvma.vm_ops = NULL;
779
	pvma.vm_policy = spol;
780
	return swapin_readahead(swap, gfp, &pvma, 0);
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}

783
static struct page *shmem_alloc_page(gfp_t gfp,
784
			struct shmem_inode_info *info, pgoff_t index)
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{
	struct vm_area_struct pvma;

788 789
	/* Create a pseudo vma that just contains the policy */
	pvma.vm_start = 0;
790
	pvma.vm_pgoff = index;
791
	pvma.vm_ops = NULL;
792
	pvma.vm_policy = mpol_shared_policy_lookup(&info->policy, index);
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	/*
	 * alloc_page_vma() will drop the shared policy reference
	 */
	return alloc_page_vma(gfp, &pvma, 0);
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}
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#else /* !CONFIG_NUMA */
#ifdef CONFIG_TMPFS
801
static inline void shmem_show_mpol(struct seq_file *seq, struct mempolicy *mpol)
802 803 804 805
{
}
#endif /* CONFIG_TMPFS */

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static inline struct page *shmem_swapin(swp_entry_t swap, gfp_t gfp,
			struct shmem_inode_info *info, pgoff_t index)
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{
809
	return swapin_readahead(swap, gfp, NULL, 0);
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}

812
static inline struct page *shmem_alloc_page(gfp_t gfp,
813
			struct shmem_inode_info *info, pgoff_t index)
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{
815
	return alloc_page(gfp);
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}
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#endif /* CONFIG_NUMA */
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#if !defined(CONFIG_NUMA) || !defined(CONFIG_TMPFS)
static inline struct mempolicy *shmem_get_sbmpol(struct shmem_sb_info *sbinfo)
{
	return NULL;
}
#endif

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/*
827
 * shmem_getpage_gfp - find page in cache, or get from swap, or allocate
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 *
 * If we allocate a new one we do not mark it dirty. That's up to the
 * vm. If we swap it in we mark it dirty since we also free the swap
 * entry since a page cannot live in both the swap and page cache
 */
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static int shmem_getpage_gfp(struct inode *inode, pgoff_t index,
834
	struct page **pagep, enum sgp_type sgp, gfp_t gfp, int *fault_type)
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{
	struct address_space *mapping = inode->i_mapping;
837
	struct shmem_inode_info *info;
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	struct shmem_sb_info *sbinfo;
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	struct page *page;
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	swp_entry_t swap;
	int error;
842
	int once = 0;
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844
	if (index > (MAX_LFS_FILESIZE >> PAGE_CACHE_SHIFT))
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		return -EFBIG;
repeat:
847
	swap.val = 0;
848
	page = find_lock_page(mapping, index);
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	if (radix_tree_exceptional_entry(page)) {
		swap = radix_to_swp_entry(page);
		page = NULL;
	}

	if (sgp != SGP_WRITE &&
	    ((loff_t)index << PAGE_CACHE_SHIFT) >= i_size_read(inode)) {
		error = -EINVAL;
		goto failed;
	}

	if (page || (sgp == SGP_READ && !swap.val)) {
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		/*
862 863 864
		 * Once we can get the page lock, it must be uptodate:
		 * if there were an error in reading back from swap,
		 * the page would not be inserted into the filecache.
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		 */
866 867 868
		BUG_ON(page && !PageUptodate(page));
		*pagep = page;
		return 0;
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	}

	/*
872 873
	 * Fast cache lookup did not find it:
	 * bring it back from swap or allocate.
874
	 */
875 876
	info = SHMEM_I(inode);
	sbinfo = SHMEM_SB(inode->i_sb);
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	if (swap.val) {
		/* Look it up and read it in.. */
880 881
		page = lookup_swap_cache(swap);
		if (!page) {
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			/* here we actually do the io */
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			if (fault_type)
				*fault_type |= VM_FAULT_MAJOR;
885
			page = shmem_swapin(swap, gfp, info, index);
886
			if (!page) {
887 888
				error = -ENOMEM;
				goto failed;
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			}
		}

		/* We have to do this with page locked to prevent races */
893
		lock_page(page);
894
		if (!PageUptodate(page)) {
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			error = -EIO;
896
			goto failed;
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		}
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		wait_on_page_writeback(page);

		/* Someone may have already done it for us */
		if (page->mapping) {
			if (page->mapping == mapping &&
			    page->index == index)
				goto done;
			error = -EEXIST;
			goto failed;
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		}
908

909 910 911 912 913
		error = mem_cgroup_cache_charge(page, current->mm,
						gfp & GFP_RECLAIM_MASK);
		if (!error)
			error = shmem_add_to_page_cache(page, mapping, index,
						gfp, swp_to_radix_entry(swap));
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		if (error)
			goto failed;

		spin_lock(&info->lock);
918
		info->swapped--;
919
		shmem_recalc_inode(inode);
920
		spin_unlock(&info->lock);
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		delete_from_swap_cache(page);
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		set_page_dirty(page);
		swap_free(swap);

926 927 928 929
	} else {
		if (shmem_acct_block(info->flags)) {
			error = -ENOSPC;
			goto failed;
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		}
931
		if (sbinfo->max_blocks) {
932
			if (percpu_counter_compare(&sbinfo->used_blocks,
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						sbinfo->max_blocks) >= 0) {
				error = -ENOSPC;
				goto unacct;
			}
937
			percpu_counter_inc(&sbinfo->used_blocks);
938
		}
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		page = shmem_alloc_page(gfp, info, index);
		if (!page) {
			error = -ENOMEM;
			goto decused;
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		}

946 947
		SetPageSwapBacked(page);
		__set_page_locked(page);
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		error = mem_cgroup_cache_charge(page, current->mm,
						gfp & GFP_RECLAIM_MASK);
		if (!error)
			error = shmem_add_to_page_cache(page, mapping, index,
						gfp, NULL);
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		if (error)
			goto decused;
		lru_cache_add_anon(page);

		spin_lock(&info->lock);
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		info->alloced++;
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		inode->i_blocks += BLOCKS_PER_PAGE;
		shmem_recalc_inode(inode);
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		spin_unlock(&info->lock);
962

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		clear_highpage(page);
		flush_dcache_page(page);
		SetPageUptodate(page);
966
		if (sgp == SGP_DIRTY)
967
			set_page_dirty(page);
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	}
done:
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	/* Perhaps the file has been truncated since we checked */
	if (sgp != SGP_WRITE &&
	    ((loff_t)index << PAGE_CACHE_SHIFT) >= i_size_read(inode)) {
		error = -EINVAL;
		goto trunc;
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	}
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	*pagep = page;
	return 0;
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978

979
	/*
980
	 * Error recovery.
981
	 */
982 983 984 985 986 987
trunc:
	ClearPageDirty(page);
	delete_from_page_cache(page);
	spin_lock(&info->lock);
	info->alloced--;
	inode->i_blocks -= BLOCKS_PER_PAGE;
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	spin_unlock(&info->lock);
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decused:
	if (sbinfo->max_blocks)
		percpu_counter_add(&sbinfo->used_blocks, -1);
unacct:
	shmem_unacct_blocks(info->flags, 1);
failed:
	if (swap.val && error != -EINVAL) {
		struct page *test = find_get_page(mapping, index);
		if (test && !radix_tree_exceptional_entry(test))
			page_cache_release(test);
		/* Have another try if the entry has changed */
		if (test != swp_to_radix_entry(swap))
			error = -EEXIST;
	}
1003
	if (page) {
1004
		unlock_page(page);
1005
		page_cache_release(page);
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	}
	if (error == -ENOSPC && !once++) {
		info = SHMEM_I(inode);
		spin_lock(&info->lock);
		shmem_recalc_inode(inode);
		spin_unlock(&info->lock);
1012
		goto repeat;
1013
	}
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	if (error == -EEXIST)
		goto repeat;
	return error;
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}

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static int shmem_fault(struct vm_area_struct *vma, struct vm_fault *vmf)
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{
1021
	struct inode *inode = vma->vm_file->f_path.dentry->d_inode;
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	int error;
1023
	int ret = VM_FAULT_LOCKED;
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1025
	error = shmem_getpage(inode, vmf->pgoff, &vmf->page, SGP_CACHE, &ret);
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	if (error)
		return ((error == -ENOMEM) ? VM_FAULT_OOM : VM_FAULT_SIGBUS);
1028

1029 1030 1031 1032
	if (ret & VM_FAULT_MAJOR) {
		count_vm_event(PGMAJFAULT);
		mem_cgroup_count_vm_event(vma->vm_mm, PGMAJFAULT);
	}
1033
	return ret;
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}

#ifdef CONFIG_NUMA
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static int shmem_set_policy(struct vm_area_struct *vma, struct mempolicy *mpol)
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{
1039 1040
	struct inode *inode = vma->vm_file->f_path.dentry->d_inode;
	return mpol_set_shared_policy(&SHMEM_I(inode)->policy, vma, mpol);
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}

1043 1044
static struct mempolicy *shmem_get_policy(struct vm_area_struct *vma,
					  unsigned long addr)
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{
1046 1047
	struct inode *inode = vma->vm_file->f_path.dentry->d_inode;
	pgoff_t index;
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	index = ((addr - vma->vm_start) >> PAGE_SHIFT) + vma->vm_pgoff;
	return mpol_shared_policy_lookup(&SHMEM_I(inode)->policy, index);
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}
#endif

int shmem_lock(struct file *file, int lock, struct user_struct *user)
{
1056
	struct inode *inode = file->f_path.dentry->d_inode;
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	struct shmem_inode_info *info = SHMEM_I(inode);
	int retval = -ENOMEM;

	spin_lock(&info->lock);
	if (lock && !(info->flags & VM_LOCKED)) {
		if (!user_shm_lock(inode->i_size, user))
			goto out_nomem;
		info->flags |= VM_LOCKED;
1065
		mapping_set_unevictable(file->f_mapping);
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	}
	if (!lock && (info->flags & VM_LOCKED) && user) {
		user_shm_unlock(inode->i_size, user);
		info->flags &= ~VM_LOCKED;
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		mapping_clear_unevictable(file->f_mapping);
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		/*
		 * Ensure that a racing putback_lru_page() can see
		 * the pages of this mapping are evictable when we
		 * skip them due to !PageLRU during the scan.
		 */
		smp_mb__after_clear_bit();
1077
		scan_mapping_unevictable_pages(file->f_mapping);
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	}
	retval = 0;
1080

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out_nomem:
	spin_unlock(&info->lock);
	return retval;
}

1086
static int shmem_mmap(struct file *file, struct vm_area_struct *vma)
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{
	file_accessed(file);
	vma->vm_ops = &shmem_vm_ops;
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	vma->vm_flags |= VM_CAN_NONLINEAR;
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	return 0;
}

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static struct inode *shmem_get_inode(struct super_block *sb, const struct inode *dir,
				     int mode, dev_t dev, unsigned long flags)
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{
	struct inode *inode;
	struct shmem_inode_info *info;
	struct shmem_sb_info *sbinfo = SHMEM_SB(sb);

1101 1102
	if (shmem_reserve_inode(sb))
		return NULL;
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	inode = new_inode(sb);
	if (inode) {
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		inode->i_ino = get_next_ino();
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		inode_init_owner(inode, dir, mode);
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		inode->i_blocks = 0;
		inode->i_mapping->backing_dev_info = &shmem_backing_dev_info;
		inode->i_atime = inode->i_mtime = inode->i_ctime = CURRENT_TIME;
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		inode->i_generation = get_seconds();
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		info = SHMEM_I(inode);
		memset(info, 0, (char *)inode - (char *)info);
		spin_lock_init(&info->lock);
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		info->flags = flags & VM_NORESERVE;
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		INIT_LIST_HEAD(&info->swaplist);
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		INIT_LIST_HEAD(&info->xattr_list);
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		cache_no_acl(inode);
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		switch (mode & S_IFMT) {
		default:
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			inode->i_op = &shmem_special_inode_operations;
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			init_special_inode(inode, mode, dev);
			break;
		case S_IFREG:
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			inode->i_mapping->a_ops = &shmem_aops;
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			inode->i_op = &shmem_inode_operations;
			inode->i_fop = &shmem_file_operations;
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			mpol_shared_policy_init(&info->policy,
						 shmem_get_sbmpol(sbinfo));
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			break;
		case S_IFDIR:
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			inc_nlink(inode);
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			/* Some things misbehave if size == 0 on a directory */
			inode->i_size = 2 * BOGO_DIRENT_SIZE;
			inode->i_op = &shmem_dir_inode_operations;
			inode->i_fop = &simple_dir_operations;
			break;
		case S_IFLNK:
			/*
			 * Must not load anything in the rbtree,
			 * mpol_free_shared_policy will not be called.
			 */
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			mpol_shared_policy_init(&info->policy, NULL);
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			break;
		}
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	} else
		shmem_free_inode(sb);
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	return inode;
}

#ifdef CONFIG_TMPFS
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static const struct inode_operations shmem_symlink_inode_operations;
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static const struct inode_operations shmem_short_symlink_operations;
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static int
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shmem_write_begin(struct file *file, struct address_space *mapping,
			loff_t pos, unsigned len, unsigned flags,
			struct page **pagep, void **fsdata)
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{
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	struct inode *inode = mapping->host;
	pgoff_t index = pos >> PAGE_CACHE_SHIFT;
	return shmem_getpage(inode, index, pagep, SGP_WRITE, NULL);
}

static int
shmem_write_end(struct file *file, struct address_space *mapping,
			loff_t pos, unsigned len, unsigned copied,
			struct page *page, void *fsdata)
{
	struct inode *inode = mapping->host;

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	if (pos + copied > inode->i_size)
		i_size_write(inode, pos + copied);

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	set_page_dirty(page);
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	unlock_page(page);
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	page_cache_release(page);

	return copied;
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}

static void do_shmem_file_read(struct file *filp, loff_t *ppos, read_descriptor_t *desc, read_actor_t actor)
{
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	struct inode *inode = filp->f_path.dentry->d_inode;
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	struct address_space *mapping = inode->i_mapping;
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	pgoff_t index;
	unsigned long offset;
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	enum sgp_type sgp = SGP_READ;

	/*
	 * Might this read be for a stacking filesystem?  Then when reading
	 * holes of a sparse file, we actually need to allocate those pages,
	 * and even mark them dirty, so it cannot exceed the max_blocks limit.
	 */
	if (segment_eq(get_fs(), KERNEL_DS))
		sgp = SGP_DIRTY;
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	index = *ppos >> PAGE_CACHE_SHIFT;
	offset = *ppos & ~PAGE_CACHE_MASK;

	for (;;) {
		struct page *page = NULL;
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		pgoff_t end_index;
		unsigned long nr, ret;
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		loff_t i_size = i_size_read(inode);

		end_index = i_size >> PAGE_CACHE_SHIFT;
		if (index > end_index)
			break;
		if (index == end_index) {
			nr = i_size & ~PAGE_CACHE_MASK;
			if (nr <= offset)
				break;
		}

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		desc->error = shmem_getpage(inode, index, &page, sgp, NULL);
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		if (desc->error) {
			if (desc->error == -EINVAL)
				desc->error = 0;
			break;
		}
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		if (page)
			unlock_page(page);
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		/*
		 * We must evaluate after, since reads (unlike writes)
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		 * are called without i_mutex protection against truncate
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		 */
		nr = PAGE_CACHE_SIZE;
		i_size = i_size_read(inode);
		end_index = i_size >> PAGE_CACHE_SHIFT;
		if (index == end_index) {
			nr = i_size & ~PAGE_CACHE_MASK;
			if (nr <= offset) {
				if (page)
					page_cache_release(page);
				break;
			}
		}
		nr -= offset;

		if (page) {
			/*
			 * If users can be writing to this page using arbitrary
			 * virtual addresses, take care about potential aliasing
			 * before reading the page on the kernel side.
			 */
			if (mapping_writably_mapped(mapping))
				flush_dcache_page(page);
			/*
			 * Mark the page accessed if we read the beginning.
			 */
			if (!offset)
				mark_page_accessed(page);