[PATCH -mm] swsusp: Freeze filesystems during suspend

["Rafael J. Wysocki" <rjw@sisk.pl>]

Freeze all filesystems during the suspend by calling freeze_bdev() for each of
them and thaw them during the resume using thaw_bdev().

This is needed by swsusp, because some filesystems (eg. XFS) use work queues
and worker_threads run with PF_NOFREEZE set, so they can cause some writes
to be performed after the suspend image has been created which may corrupt
the filesystem.  The additional benefit of it is that if the resume fails, the
filesystems will be in a consistent state and there won't be any journal replays
needed.

The freezing of filesystems is carried out when processes are being frozen, so
on the majority of architectures it also will happen during a suspend to RAM.

Signed-off-by: Nigel Cunningham <nigel@suspend2.net>
Signed-off-by: Rafael J. Wysocki <rjw@sisk.pl>
---
 fs/buffer.c                 |   44 ++++++++++++++++++++++++++++++++++++++
 include/linux/buffer_head.h |    2 +
 include/linux/fs.h          |    1 
 kernel/power/process.c      |   50 +++++++++++++++++++++++++++++---------------
 4 files changed, 80 insertions(+), 17 deletions(-)

Index: linux-2.6.19-rc4-mm1/kernel/power/process.c
===================================================================
--- linux-2.6.19-rc4-mm1.orig/kernel/power/process.c	2006-10-31 22:40:40.000000000 +0100
+++ linux-2.6.19-rc4-mm1/kernel/power/process.c	2006-10-31 22:41:03.000000000 +0100
@@ -14,6 +14,7 @@
 #include <linux/module.h>
 #include <linux/syscalls.h>
 #include <linux/freezer.h>
+#include <linux/buffer_head.h>
 
 /* 
  * Timeout for stopping processes
@@ -119,7 +120,7 @@ int freeze_processes(void)
 		read_unlock(&tasklist_lock);
 		todo += nr_user;
 		if (!user_frozen && !nr_user) {
-			sys_sync();
+			freeze_filesystems();
 			start_time = jiffies;
 		}
 		user_frozen = !nr_user;
@@ -156,28 +157,43 @@ int freeze_processes(void)
 void thaw_some_processes(int all)
 {
 	struct task_struct *g, *p;
-	int pass = 0; /* Pass 0 = Kernel space, 1 = Userspace */
 
 	printk("Restarting tasks... ");
 	read_lock(&tasklist_lock);
-	do {
-		do_each_thread(g, p) {
-			/*
-			 * is_user = 0 if kernel thread or borrowed mm,
-			 * 1 otherwise.
-			 */
-			int is_user = !!(p->mm && !(p->flags & PF_BORROWED_MM));
-			if (!freezeable(p) || (is_user != pass))
-				continue;
-			if (!thaw_process(p))
-				printk(KERN_INFO
-					"Strange, %s not stopped\n", p->comm);
-		} while_each_thread(g, p);
 
-		pass++;
-	} while (pass < 2 && all);
+	do_each_thread(g, p) {
+		if (!freezeable(p))
+			continue;
+
+		/* Don't thaw userland processes, for now */
+		if (p->mm && !(p->flags & PF_BORROWED_MM))
+			continue;
+
+		if (!thaw_process(p))
+			printk(KERN_INFO " Strange, %s not stopped\n", p->comm );
+	} while_each_thread(g, p);
+
+	read_unlock(&tasklist_lock);
+	if (!all)
+		goto Exit;
+
+	thaw_filesystems();
+	read_lock(&tasklist_lock);
+
+	do_each_thread(g, p) {
+		if (!freezeable(p))
+			continue;
+
+		/* Kernel threads should have been thawed already */
+		if (!p->mm || (p->flags & PF_BORROWED_MM))
+			continue;
+
+		if (!thaw_process(p))
+			printk(KERN_INFO " Strange, %s not stopped\n", p->comm );
+	} while_each_thread(g, p);
 
 	read_unlock(&tasklist_lock);
+Exit:
 	schedule();
 	printk("done.\n");
 }
Index: linux-2.6.19-rc4-mm1/include/linux/buffer_head.h
===================================================================
--- linux-2.6.19-rc4-mm1.orig/include/linux/buffer_head.h	2006-10-31 22:40:36.000000000 +0100
+++ linux-2.6.19-rc4-mm1/include/linux/buffer_head.h	2006-10-31 22:41:03.000000000 +0100
@@ -170,6 +170,8 @@ wait_queue_head_t *bh_waitq_head(struct 
 int fsync_bdev(struct block_device *);
 struct super_block *freeze_bdev(struct block_device *);
 void thaw_bdev(struct block_device *, struct super_block *);
+void freeze_filesystems(void);
+void thaw_filesystems(void);
 int fsync_super(struct super_block *);
 int fsync_no_super(struct block_device *);
 struct buffer_head *__find_get_block(struct block_device *, sector_t, int);
Index: linux-2.6.19-rc4-mm1/include/linux/fs.h
===================================================================
--- linux-2.6.19-rc4-mm1.orig/include/linux/fs.h	2006-10-31 22:40:36.000000000 +0100
+++ linux-2.6.19-rc4-mm1/include/linux/fs.h	2006-10-31 22:41:03.000000000 +0100
@@ -120,6 +120,7 @@ extern int dir_notify_enable;
 #define MS_PRIVATE	(1<<18)	/* change to private */
 #define MS_SLAVE	(1<<19)	/* change to slave */
 #define MS_SHARED	(1<<20)	/* change to shared */
+#define MS_FROZEN	(1<<21)	/* Frozen by freeze_filesystems() */
 #define MS_ACTIVE	(1<<30)
 #define MS_NOUSER	(1<<31)
 
Index: linux-2.6.19-rc4-mm1/fs/buffer.c
===================================================================
--- linux-2.6.19-rc4-mm1.orig/fs/buffer.c	2006-10-31 22:40:35.000000000 +0100
+++ linux-2.6.19-rc4-mm1/fs/buffer.c	2006-10-31 23:20:09.000000000 +0100
@@ -244,6 +244,50 @@ void thaw_bdev(struct block_device *bdev
 }
 EXPORT_SYMBOL(thaw_bdev);
 
+/**
+ * freeze_filesystems - lock all filesystems and force them into a consistent
+ * state
+ */
+void freeze_filesystems(void)
+{
+	struct super_block *sb;
+
+	lockdep_off();
+	/*
+	 * Freeze in reverse order so filesystems dependant upon others are
+	 * frozen in the right order (eg. loopback on ext3).
+	 */
+	list_for_each_entry_reverse(sb, &super_blocks, s_list) {
+		if (!sb->s_root || !sb->s_bdev ||
+		    (sb->s_frozen == SB_FREEZE_TRANS) ||
+		    (sb->s_flags & MS_RDONLY) ||
+		    (sb->s_flags & MS_FROZEN))
+			continue;
+
+		freeze_bdev(sb->s_bdev);
+		sb->s_flags |= MS_FROZEN;
+	}
+	lockdep_on();
+}
+
+/**
+ * thaw_filesystems - unlock all filesystems
+ */
+void thaw_filesystems(void)
+{
+	struct super_block *sb;
+
+	lockdep_off();
+
+	list_for_each_entry(sb, &super_blocks, s_list)
+		if (sb->s_flags & MS_FROZEN) {
+			sb->s_flags &= ~MS_FROZEN;
+			thaw_bdev(sb->s_bdev, sb);
+		}
+
+	lockdep_on();
+}
+
 /*
  * Various filesystems appear to want __find_get_block to be non-blocking.
  * But it's the page lock which protects the buffers.  To get around this,