2 files changed, 117 insertions, 94 deletions

diff --git a/include/linux/swap.h b/include/linux/swap.h
index 82aa7e1..f1c2487 100644
--- a/include/linux/swap.h
+++ b/include/linux/swap.h
@@ -159,9 +159,10 @@ enum {
  * The in-memory structure used to track swap areas.
  */
 struct swap_info_struct {
-	unsigned long flags;
-	int prio;			/* swap priority */
-	int next;			/* next entry on swap list */
+	unsigned long	flags;		/* SWP_USED etc: see above */
+	signed short	prio;		/* swap priority of this type */
+	signed char	type;		/* strange name for an index */
+	signed char	next;		/* next type on the swap list */
 	struct file *swap_file;
 	struct block_device *bdev;
 	struct list_head extent_list;
diff --git a/mm/swapfile.c b/mm/swapfile.c
index f83f1c6..dc88a7e 100644
--- a/mm/swapfile.c
+++ b/mm/swapfile.c
@@ -49,7 +49,7 @@ static const char Unused_offset[] = "Unused swap offset entry ";
 
 static struct swap_list_t swap_list = {-1, -1};
 
-static struct swap_info_struct swap_info[MAX_SWAPFILES];
+static struct swap_info_struct *swap_info[MAX_SWAPFILES];
 
 static DEFINE_MUTEX(swapon_mutex);
 
@@ -79,12 +79,11 @@ static inline unsigned short encode_swapmap(int count, bool has_cache)
 	return ret;
 }
 
-/* returnes 1 if swap entry is freed */
+/* returns 1 if swap entry is freed */
 static int
 __try_to_reclaim_swap(struct swap_info_struct *si, unsigned long offset)
 {
-	int type = si - swap_info;
-	swp_entry_t entry = swp_entry(type, offset);
+	swp_entry_t entry = swp_entry(si->type, offset);
 	struct page *page;
 	int ret = 0;
 
@@ -120,7 +119,7 @@ void swap_unplug_io_fn(struct backing_dev_info *unused_bdi, struct page *page)
 	down_read(&swap_unplug_sem);
 	entry.val = page_private(page);
 	if (PageSwapCache(page)) {
-		struct block_device *bdev = swap_info[swp_type(entry)].bdev;
+		struct block_device *bdev = swap_info[swp_type(entry)]->bdev;
 		struct backing_dev_info *bdi;
 
 		/*
@@ -467,10 +466,10 @@ swp_entry_t get_swap_page(void)
 	nr_swap_pages--;
 
 	for (type = swap_list.next; type >= 0 && wrapped < 2; type = next) {
-		si = swap_info + type;
+		si = swap_info[type];
 		next = si->next;
 		if (next < 0 ||
-		    (!wrapped && si->prio != swap_info[next].prio)) {
+		    (!wrapped && si->prio != swap_info[next]->prio)) {
 			next = swap_list.head;
 			wrapped++;
 		}
@@ -503,8 +502,8 @@ swp_entry_t get_swap_page_of_type(int type)
 	pgoff_t offset;
 
 	spin_lock(&swap_lock);
-	si = swap_info + type;
-	if (si->flags & SWP_WRITEOK) {
+	si = swap_info[type];
+	if (si && (si->flags & SWP_WRITEOK)) {
 		nr_swap_pages--;
 		/* This is called for allocating swap entry, not cache */
 		offset = scan_swap_map(si, SWAP_MAP);
@@ -528,7 +527,7 @@ static struct swap_info_struct * swap_info_get(swp_entry_t entry)
 	type = swp_type(entry);
 	if (type >= nr_swapfiles)
 		goto bad_nofile;
-	p = & swap_info[type];
+	p = swap_info[type];
 	if (!(p->flags & SWP_USED))
 		goto bad_device;
 	offset = swp_offset(entry);
@@ -581,8 +580,9 @@ static int swap_entry_free(struct swap_info_struct *p,
 			p->lowest_bit = offset;
 		if (offset > p->highest_bit)
 			p->highest_bit = offset;
-		if (p->prio > swap_info[swap_list.next].prio)
-			swap_list.next = p - swap_info;
+		if (swap_list.next >= 0 &&
+		    p->prio > swap_info[swap_list.next]->prio)
+			swap_list.next = p->type;
 		nr_swap_pages++;
 		p->inuse_pages--;
 	}
@@ -741,14 +741,14 @@ int free_swap_and_cache(swp_entry_t entry)
 int swap_type_of(dev_t device, sector_t offset, struct block_device **bdev_p)
 {
 	struct block_device *bdev = NULL;
-	int i;
+	int type;
 
 	if (device)
 		bdev = bdget(device);
 
 	spin_lock(&swap_lock);
-	for (i = 0; i < nr_swapfiles; i++) {
-		struct swap_info_struct *sis = swap_info + i;
+	for (type = 0; type < nr_swapfiles; type++) {
+		struct swap_info_struct *sis = swap_info[type];
 
 		if (!(sis->flags & SWP_WRITEOK))
 			continue;
@@ -758,7 +758,7 @@ int swap_type_of(dev_t device, sector_t offset, struct block_device **bdev_p)
 				*bdev_p = bdgrab(sis->bdev);
 
 			spin_unlock(&swap_lock);
-			return i;
+			return type;
 		}
 		if (bdev == sis->bdev) {
 			struct swap_extent *se;
@@ -771,7 +771,7 @@ int swap_type_of(dev_t device, sector_t offset, struct block_device **bdev_p)
 
 				spin_unlock(&swap_lock);
 				bdput(bdev);
-				return i;
+				return type;
 			}
 		}
 	}
@@ -792,15 +792,17 @@ unsigned int count_swap_pages(int type, int free)
 {
 	unsigned int n = 0;
 
-	if (type < nr_swapfiles) {
-		spin_lock(&swap_lock);
-		if (swap_info[type].flags & SWP_WRITEOK) {
-			n = swap_info[type].pages;
+	spin_lock(&swap_lock);
+	if ((unsigned int)type < nr_swapfiles) {
+		struct swap_info_struct *sis = swap_info[type];
+
+		if (sis->flags & SWP_WRITEOK) {
+			n = sis->pages;
 			if (free)
-				n -= swap_info[type].inuse_pages;
+				n -= sis->inuse_pages;
 		}
-		spin_unlock(&swap_lock);
 	}
+	spin_unlock(&swap_lock);
 	return n;
 }
 #endif
@@ -1024,7 +1026,7 @@ static unsigned int find_next_to_unuse(struct swap_info_struct *si,
  */
 static int try_to_unuse(unsigned int type)
 {
-	struct swap_info_struct * si = &swap_info[type];
+	struct swap_info_struct *si = swap_info[type];
 	struct mm_struct *start_mm;
 	unsigned short *swap_map;
 	unsigned short swcount;
@@ -1270,10 +1272,10 @@ retry:
 static void drain_mmlist(void)
 {
 	struct list_head *p, *next;
-	unsigned int i;
+	unsigned int type;
 
-	for (i = 0; i < nr_swapfiles; i++)
-		if (swap_info[i].inuse_pages)
+	for (type = 0; type < nr_swapfiles; type++)
+		if (swap_info[type]->inuse_pages)
 			return;
 	spin_lock(&mmlist_lock);
 	list_for_each_safe(p, next, &init_mm.mmlist)
@@ -1293,7 +1295,7 @@ sector_t map_swap_page(swp_entry_t entry, struct block_device **bdev)
 	struct swap_extent *se;
 	pgoff_t offset;
 
-	sis = swap_info + swp_type(entry);
+	sis = swap_info[swp_type(entry)];
 	*bdev = sis->bdev;
 
 	offset = swp_offset(entry);
@@ -1321,17 +1323,15 @@ sector_t map_swap_page(swp_entry_t entry, struct block_device **bdev)
  * Get the (PAGE_SIZE) block corresponding to given offset on the swapdev
  * corresponding to given index in swap_info (swap type).
  */
-sector_t swapdev_block(int swap_type, pgoff_t offset)
+sector_t swapdev_block(int type, pgoff_t offset)
 {
-	struct swap_info_struct *sis;
 	struct block_device *bdev;
 
-	if (swap_type >= nr_swapfiles)
+	if ((unsigned int)type >= nr_swapfiles)
 		return 0;
-
-	sis = swap_info + swap_type;
-	return (sis->flags & SWP_WRITEOK) ?
-		map_swap_page(swp_entry(swap_type, offset), &bdev) : 0;
+	if (!(swap_info[type]->flags & SWP_WRITEOK))
+		return 0;
+	return map_swap_page(swp_entry(type, offset), &bdev);
 }
 #endif /* CONFIG_HIBERNATION */
 
@@ -1547,8 +1547,8 @@ SYSCALL_DEFINE1(swapoff, const char __user *, specialfile)
 	mapping = victim->f_mapping;
 	prev = -1;
 	spin_lock(&swap_lock);
-	for (type = swap_list.head; type >= 0; type = swap_info[type].next) {
-		p = swap_info + type;
+	for (type = swap_list.head; type >= 0; type = swap_info[type]->next) {
+		p = swap_info[type];
 		if (p->flags & SWP_WRITEOK) {
 			if (p->swap_file->f_mapping == mapping)
 				break;
@@ -1567,18 +1567,17 @@ SYSCALL_DEFINE1(swapoff, const char __user *, specialfile)
 		spin_unlock(&swap_lock);
 		goto out_dput;
 	}
-	if (prev < 0) {
+	if (prev < 0)
 		swap_list.head = p->next;
-	} else {
-		swap_info[prev].next = p->next;
-	}
+	else
+		swap_info[prev]->next = p->next;
 	if (type == swap_list.next) {
 		/* just pick something that's safe... */
 		swap_list.next = swap_list.head;
 	}
 	if (p->prio < 0) {
-		for (i = p->next; i >= 0; i = swap_info[i].next)
-			swap_info[i].prio = p->prio--;
+		for (i = p->next; i >= 0; i = swap_info[i]->next)
+			swap_info[i]->prio = p->prio--;
 		least_priority++;
 	}
 	nr_swap_pages -= p->pages;
@@ -1596,16 +1595,16 @@ SYSCALL_DEFINE1(swapoff, const char __user *, specialfile)
 		if (p->prio < 0)
 			p->prio = --least_priority;
 		prev = -1;
-		for (i = swap_list.head; i >= 0; i = swap_info[i].next) {
-			if (p->prio >= swap_info[i].prio)
+		for (i = swap_list.head; i >= 0; i = swap_info[i]->next) {
+			if (p->prio >= swap_info[i]->prio)
 				break;
 			prev = i;
 		}
 		p->next = i;
 		if (prev < 0)
-			swap_list.head = swap_list.next = p - swap_info;
+			swap_list.head = swap_list.next = type;
 		else
-			swap_info[prev].next = p - swap_info;
+			swap_info[prev]->next = type;
 		nr_swap_pages += p->pages;
 		total_swap_pages += p->pages;
 		p->flags |= SWP_WRITEOK;
@@ -1665,8 +1664,8 @@ out:
 /* iterator */
 static void *swap_start(struct seq_file *swap, loff_t *pos)
 {
-	struct swap_info_struct *ptr = swap_info;
-	int i;
+	struct swap_info_struct *si;
+	int type;
 	loff_t l = *pos;
 
 	mutex_lock(&swapon_mutex);
@@ -1674,11 +1673,13 @@ static void *swap_start(struct seq_file *swap, loff_t *pos)
 	if (!l)
 		return SEQ_START_TOKEN;
 
-	for (i = 0; i < nr_swapfiles; i++, ptr++) {
-		if (!(ptr->flags & SWP_USED) || !ptr->swap_map)
+	for (type = 0; type < nr_swapfiles; type++) {
+		smp_rmb();	/* read nr_swapfiles before swap_info[type] */
+		si = swap_info[type];
+		if (!(si->flags & SWP_USED) || !si->swap_map)
 			continue;
 		if (!--l)
-			return ptr;
+			return si;
 	}
 
 	return NULL;
@@ -1686,21 +1687,21 @@ static void *swap_start(struct seq_file *swap, loff_t *pos)
 
 static void *swap_next(struct seq_file *swap, void *v, loff_t *pos)
 {
-	struct swap_info_struct *ptr;
-	struct swap_info_struct *endptr = swap_info + nr_swapfiles;
+	struct swap_info_struct *si = v;
+	int type;
 
 	if (v == SEQ_START_TOKEN)
-		ptr = swap_info;
-	else {
-		ptr = v;
-		ptr++;
-	}
+		type = 0;
+	else
+		type = si->type + 1;
 
-	for (; ptr < endptr; ptr++) {
-		if (!(ptr->flags & SWP_USED) || !ptr->swap_map)
+	for (; type < nr_swapfiles; type++) {
+		smp_rmb();	/* read nr_swapfiles before swap_info[type] */
+		si = swap_info[type];
+		if (!(si->flags & SWP_USED) || !si->swap_map)
 			continue;
 		++*pos;
-		return ptr;
+		return si;
 	}
 
 	return NULL;
@@ -1713,24 +1714,24 @@ static void swap_stop(struct seq_file *swap, void *v)
 
 static int swap_show(struct seq_file *swap, void *v)
 {
-	struct swap_info_struct *ptr = v;
+	struct swap_info_struct *si = v;
 	struct file *file;
 	int len;
 
-	if (ptr == SEQ_START_TOKEN) {
+	if (si == SEQ_START_TOKEN) {
 		seq_puts(swap,"Filename\t\t\t\tType\t\tSize\tUsed\tPriority\n");
 		return 0;
 	}
 
-	file = ptr->swap_file;
+	file = si->swap_file;
 	len = seq_path(swap, &file->f_path, " \t\n\\");
 	seq_printf(swap, "%*s%s\t%u\t%u\t%d\n",
 			len < 40 ? 40 - len : 1, " ",
 			S_ISBLK(file->f_path.dentry->d_inode->i_mode) ?
 				"partition" : "file\t",
-			ptr->pages << (PAGE_SHIFT - 10),
-			ptr->inuse_pages << (PAGE_SHIFT - 10),
-			ptr->prio);
+			si->pages << (PAGE_SHIFT - 10),
+			si->inuse_pages << (PAGE_SHIFT - 10),
+			si->prio);
 	return 0;
 }
 
@@ -1798,23 +1799,45 @@ SYSCALL_DEFINE2(swapon, const char __user *, specialfile, int, swap_flags)
 
 	if (!capable(CAP_SYS_ADMIN))
 		return -EPERM;
+
+	p = kzalloc(sizeof(*p), GFP_KERNEL);
+	if (!p)
+		return -ENOMEM;
+
 	spin_lock(&swap_lock);
-	p = swap_info;
-	for (type = 0 ; type < nr_swapfiles ; type++,p++)
-		if (!(p->flags & SWP_USED))
+	for (type = 0; type < nr_swapfiles; type++) {
+		if (!(swap_info[type]->flags & SWP_USED))
 			break;
+	}
 	error = -EPERM;
 	if (type >= MAX_SWAPFILES) {
 		spin_unlock(&swap_lock);
+		kfree(p);
 		goto out;
 	}
-	if (type >= nr_swapfiles)
-		nr_swapfiles = type+1;
-	memset(p, 0, sizeof(*p));
 	INIT_LIST_HEAD(&p->extent_list);
+	if (type >= nr_swapfiles) {
+		p->type = type;
+		swap_info[type] = p;
+		/*
+		 * Write swap_info[type] before nr_swapfiles, in case a
+		 * racing procfs swap_start() or swap_next() is reading them.
+		 * (We never shrink nr_swapfiles, we never free this entry.)
+		 */
+		smp_wmb();
+		nr_swapfiles++;
+	} else {
+		kfree(p);
+		p = swap_info[type];
+		/*
+		 * Do not memset this entry: a racing procfs swap_next()
+		 * would be relying on p->type to remain valid.
+		 */
+	}
 	p->flags = SWP_USED;
 	p->next = -1;
 	spin_unlock(&swap_lock);
+
 	name = getname(specialfile);
 	error = PTR_ERR(name);
 	if (IS_ERR(name)) {
@@ -1834,7 +1857,7 @@ SYSCALL_DEFINE2(swapon, const char __user *, specialfile, int, swap_flags)
 
 	error = -EBUSY;
 	for (i = 0; i < nr_swapfiles; i++) {
-		struct swap_info_struct *q = &swap_info[i];
+		struct swap_info_struct *q = swap_info[i];
 
 		if (i == type || !q->swap_file)
 			continue;
@@ -1909,6 +1932,7 @@ SYSCALL_DEFINE2(swapon, const char __user *, specialfile, int, swap_flags)
 
 	p->lowest_bit  = 1;
 	p->cluster_next = 1;
+	p->cluster_nr = 0;
 
 	/*
 	 * Find out how many pages are allowed for a single swap
@@ -2015,18 +2039,16 @@ SYSCALL_DEFINE2(swapon, const char __user *, specialfile, int, swap_flags)
 
 	/* insert swap space into swap_list: */
 	prev = -1;
-	for (i = swap_list.head; i >= 0; i = swap_info[i].next) {
-		if (p->prio >= swap_info[i].prio) {
+	for (i = swap_list.head; i >= 0; i = swap_info[i]->next) {
+		if (p->prio >= swap_info[i]->prio)
 			break;
-		}
 		prev = i;
 	}
 	p->next = i;
-	if (prev < 0) {
-		swap_list.head = swap_list.next = p - swap_info;
-	} else {
-		swap_info[prev].next = p - swap_info;
-	}
+	if (prev < 0)
+		swap_list.head = swap_list.next = type;
+	else
+		swap_info[prev]->next = type;
 	spin_unlock(&swap_lock);
 	mutex_unlock(&swapon_mutex);
 	error = 0;
@@ -2063,15 +2085,15 @@ out:
 
 void si_swapinfo(struct sysinfo *val)
 {
-	unsigned int i;
+	unsigned int type;
 	unsigned long nr_to_be_unused = 0;
 
 	spin_lock(&swap_lock);
-	for (i = 0; i < nr_swapfiles; i++) {
-		if (!(swap_info[i].flags & SWP_USED) ||
-		     (swap_info[i].flags & SWP_WRITEOK))
-			continue;
-		nr_to_be_unused += swap_info[i].inuse_pages;
+	for (type = 0; type < nr_swapfiles; type++) {
+		struct swap_info_struct *si = swap_info[type];
+
+		if ((si->flags & SWP_USED) && !(si->flags & SWP_WRITEOK))
+			nr_to_be_unused += si->inuse_pages;
 	}
 	val->freeswap = nr_swap_pages + nr_to_be_unused;
 	val->totalswap = total_swap_pages + nr_to_be_unused;
@@ -2104,7 +2126,7 @@ static int __swap_duplicate(swp_entry_t entry, bool cache)
 	type = swp_type(entry);
 	if (type >= nr_swapfiles)
 		goto bad_file;
-	p = type + swap_info;
+	p = swap_info[type];
 	offset = swp_offset(entry);
 
 	spin_lock(&swap_lock);
@@ -2186,7 +2208,7 @@ int valid_swaphandles(swp_entry_t entry, unsigned long *offset)
 	if (!our_page_cluster)	/* no readahead */
 		return 0;
 
-	si = &swap_info[swp_type(entry)];
+	si = swap_info[swp_type(entry)];
 	target = swp_offset(entry);
 	base = (target >> our_page_cluster) << our_page_cluster;
 	end = base + (1 << our_page_cluster);