hibernation: freeze swap at hibernation

When taking a memory snapshot in hibernate_snapshot(), all (directly
called) memory allocations use GFP_ATOMIC.  Hence swap misusage during
hibernation never occurs.

But from a pessimistic point of view, there is no guarantee that no page
allcation has __GFP_WAIT.  It is better to have a global indication "we
enter hibernation, don't use swap!".

This patch tries to freeze new-swap-allocation during hibernation.  (All
user processes are frozenm so swapin is not a concern).

This way, no updates will happen to swap_map[] between
hibernate_snapshot() and save_image().  Swap is thawed when swsusp_free()
is called.  We can be assured that swap corruption will not occur.

Signed-off-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: "Rafael J. Wysocki" <rjw@sisk.pl>
Cc: Hugh Dickins <hughd@google.com>
Cc: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
Cc: Ondrej Zary <linux@rainbow-software.org>
Cc: Balbir Singh <balbir@in.ibm.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

5 files changed, 84 insertions, 26 deletions

diff --git a/include/linux/swap.h b/include/linux/swap.h
index ff4acea9bbdb..91c9d3fc8513 100644
--- a/include/linux/swap.h
+++ b/include/linux/swap.h
@@ -316,7 +316,6 @@ extern long nr_swap_pages;
 extern long total_swap_pages;
 extern void si_swapinfo(struct sysinfo *);
 extern swp_entry_t get_swap_page(void);
-extern swp_entry_t get_swap_page_of_type(int);
 extern int valid_swaphandles(swp_entry_t, unsigned long *);
 extern int add_swap_count_continuation(swp_entry_t, gfp_t);
 extern void swap_shmem_alloc(swp_entry_t);
@@ -333,6 +332,13 @@ extern int reuse_swap_page(struct page *);
 extern int try_to_free_swap(struct page *);
 struct backing_dev_info;
 
+#ifdef CONFIG_HIBERNATION
+void hibernation_freeze_swap(void);
+void hibernation_thaw_swap(void);
+swp_entry_t get_swap_for_hibernation(int type);
+void swap_free_for_hibernation(swp_entry_t val);
+#endif
+
 /* linux/mm/thrash.c */
 extern struct mm_struct *swap_token_mm;
 extern void grab_swap_token(struct mm_struct *);
diff --git a/kernel/power/hibernate.c b/kernel/power/hibernate.c
index 8dc31e02ae12..c77963938bca 100644
--- a/kernel/power/hibernate.c
+++ b/kernel/power/hibernate.c
@@ -338,6 +338,7 @@ int hibernation_snapshot(int platform_mode)
                 goto Close;
 
         suspend_console();
+        hibernation_freeze_swap();
         saved_mask = clear_gfp_allowed_mask(GFP_IOFS);
         error = dpm_suspend_start(PMSG_FREEZE);
         if (error)
diff --git a/kernel/power/snapshot.c b/kernel/power/snapshot.c
index f6cd6faf84fd..5e7edfb05e66 100644
--- a/kernel/power/snapshot.c
+++ b/kernel/power/snapshot.c
@@ -1086,6 +1086,7 @@ void swsusp_free(void)
         buffer = NULL;
         alloc_normal = 0;
         alloc_highmem = 0;
+        hibernation_thaw_swap();
 }
 
 /* Helper functions used for the shrinking of memory. */
diff --git a/kernel/power/swap.c b/kernel/power/swap.c
index e6a5bdf61a37..5d0059eed3e4 100644
--- a/kernel/power/swap.c
+++ b/kernel/power/swap.c
@@ -136,10 +136,10 @@ sector_t alloc_swapdev_block(int swap)
 {
         unsigned long offset;
 
-        offset = swp_offset(get_swap_page_of_type(swap));
+        offset = swp_offset(get_swap_for_hibernation(swap));
         if (offset) {
                 if (swsusp_extents_insert(offset))
-                        swap_free(swp_entry(swap, offset));
+                        swap_free_for_hibernation(swp_entry(swap, offset));
                 else
                         return swapdev_block(swap, offset);
         }
@@ -163,7 +163,7 @@ void free_all_swap_pages(int swap)
                 ext = container_of(node, struct swsusp_extent, node);
                 rb_erase(node, &swsusp_extents);
                 for (offset = ext->start; offset <= ext->end; offset++)
-                        swap_free(swp_entry(swap, offset));
+                        swap_free_for_hibernation(swp_entry(swap, offset));
 
                 kfree(ext);
         }
diff --git a/mm/swapfile.c b/mm/swapfile.c
index f08d165871b3..1f3f9c59a73a 100644
--- a/mm/swapfile.c
+++ b/mm/swapfile.c
@@ -47,6 +47,8 @@ long nr_swap_pages;
 long total_swap_pages;
 static int least_priority;
 
+static bool swap_for_hibernation;
+
 static const char Bad_file[] = "Bad swap file entry ";
 static const char Unused_file[] = "Unused swap file entry ";
 static const char Bad_offset[] = "Bad swap offset entry ";
@@ -451,6 +453,8 @@ swp_entry_t get_swap_page(void)
         spin_lock(&swap_lock);
         if (nr_swap_pages <= 0)
                 goto noswap;
+        if (swap_for_hibernation)
+                goto noswap;
         nr_swap_pages--;
 
         for (type = swap_list.next; type >= 0 && wrapped < 2; type = next) {
@@ -483,28 +487,6 @@ noswap:
         return (swp_entry_t) {0};
 }
 
-/* The only caller of this function is now susupend routine */
-swp_entry_t get_swap_page_of_type(int type)
-{
-        struct swap_info_struct *si;
-        pgoff_t offset;
-
-        spin_lock(&swap_lock);
-        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, 1);
-                if (offset) {
-                        spin_unlock(&swap_lock);
-                        return swp_entry(type, offset);
-                }
-                nr_swap_pages++;
-        }
-        spin_unlock(&swap_lock);
-        return (swp_entry_t) {0};
-}
-
 static struct swap_info_struct *swap_info_get(swp_entry_t entry)
 {
         struct swap_info_struct *p;
@@ -764,6 +746,74 @@ int mem_cgroup_count_swap_user(swp_entry_t ent, struct page **pagep)
 #endif
 
 #ifdef CONFIG_HIBERNATION
+
+static pgoff_t hibernation_offset[MAX_SWAPFILES];
+/*
+ * Once hibernation starts to use swap, we freeze swap_map[]. Otherwise,
+ * saved swap_map[] image to the disk will be an incomplete because it's
+ * changing without synchronization with hibernation snap shot.
+ * At resume, we just make swap_for_hibernation=false. We can forget
+ * used maps easily.
+ */
+void hibernation_freeze_swap(void)
+{
+        int i;
+
+        spin_lock(&swap_lock);
+
+        printk(KERN_INFO "PM: Freeze Swap\n");
+        swap_for_hibernation = true;
+        for (i = 0; i < MAX_SWAPFILES; i++)
+                hibernation_offset[i] = 1;
+        spin_unlock(&swap_lock);
+}
+
+void hibernation_thaw_swap(void)
+{
+        spin_lock(&swap_lock);
+        if (swap_for_hibernation) {
+                printk(KERN_INFO "PM: Thaw Swap\n");
+                swap_for_hibernation = false;
+        }
+        spin_unlock(&swap_lock);
+}
+
+/*
+ * Because updateing swap_map[] can make not-saved-status-change,
+ * we use our own easy allocator.
+ * Please see kernel/power/swap.c, Used swaps are recorded into
+ * RB-tree.
+ */
+swp_entry_t get_swap_for_hibernation(int type)
+{
+        pgoff_t off;
+        swp_entry_t val = {0};
+        struct swap_info_struct *si;
+
+        spin_lock(&swap_lock);
+
+        si = swap_info[type];
+        if (!si || !(si->flags & SWP_WRITEOK))
+                goto done;
+
+        for (off = hibernation_offset[type]; off < si->max; ++off) {
+                if (!si->swap_map[off])
+                        break;
+        }
+        if (off < si->max) {
+                val = swp_entry(type, off);
+                hibernation_offset[type] = off + 1;
+        }
+done:
+        spin_unlock(&swap_lock);
+        return val;
+}
+
+void swap_free_for_hibernation(swp_entry_t ent)
+{
+        /* Nothing to do */
+}
+
 /*
  * Find the swap type that corresponds to given device (if any).
  *