From: Rafael J. Wysocki <redacted>

Freeze all filesystems during the freezing of tasks by calling
freeze_bdev() for each of them and thaw them during the thawing
of tasks with the help of thaw_bdev().

This is needed by hibernation, because some filesystems (e.g. XFS)
deadlock with the preallocation of memory used by it if the memory
pressure caused by it is too heavy.

The additional benefit of this change is that, if something goes
wrong after filesystems have been frozen, they will stay in a
consistent state and journal replays won't be necessary (e.g. after
a failing suspend or resume).  In particular, this should help to
solve a long-standing issue that in some cases during resume from
hibernation the boot loader causes the journal to be replied for the
filesystem containing the kernel image and initrd causing it to
become inconsistent with the information stored in the hibernation
image.

This change is based on earlier work by Nigel Cunningham.

Signed-off-by: Rafael J. Wysocki <redacted>
---

OK, so nobody except for Pavel appears to have any comments, so I assume
that everyone except for Pavel is fine with the approach, interestingly enough.

I've removed the MS_FROZEN Pavel complained about from freeze_filesystems()
and added comments explaining why lockdep_off/on() are used.

Thanks,
Rafael

---
 fs/block_dev.c         |   56 +++++++++++++++++++++++++++++++++++++++++++++++++
 include/linux/fs.h     |    6 +++++
 kernel/power/process.c |    7 +++++-
 3 files changed, 68 insertions(+), 1 deletion(-)

Index: linux-2.6/include/linux/fs.h
===================================================================

--- linux-2.6.orig/include/linux/fs.h
+++ linux-2.6/include/linux/fs.h

@@ -211,6 +211,7 @@ struct inodes_stat_t {
 #define MS_KERNMOUNT	(1<<22) /* this is a kern_mount call */
 #define MS_I_VERSION	(1<<23) /* Update inode I_version field */
 #define MS_STRICTATIME	(1<<24) /* Always perform atime updates */
+#define MS_FROZEN	(1<<25) /* bdev has been frozen */
 #define MS_NOSEC	(1<<28)
 #define MS_BORN		(1<<29)
 #define MS_ACTIVE	(1<<30)

@@ -2047,6 +2048,8 @@ extern struct super_block *freeze_bdev(s
 extern void emergency_thaw_all(void);
 extern int thaw_bdev(struct block_device *bdev, struct super_block *sb);
 extern int fsync_bdev(struct block_device *);
+extern void freeze_filesystems(void);
+extern void thaw_filesystems(void);
 #else
 static inline void bd_forget(struct inode *inode) {}
 static inline int sync_blockdev(struct block_device *bdev) { return 0; }

@@ -2061,6 +2064,9 @@ static inline int thaw_bdev(struct block
 {
 	return 0;
 }
+
+static inline void freeze_filesystems(void) {}
+static inline void thaw_filesystems(void) {}
 #endif
 extern int sync_filesystem(struct super_block *);
 extern const struct file_operations def_blk_fops;

Index: linux-2.6/fs/block_dev.c
===================================================================

--- linux-2.6.orig/fs/block_dev.c
+++ linux-2.6/fs/block_dev.c

@@ -314,6 +314,62 @@ out:
 }
 EXPORT_SYMBOL(thaw_bdev);
 
+/**
+ * freeze_filesystems - Force all filesystems into a consistent state.
+ */
+void freeze_filesystems(void)
+{
+	struct super_block *sb;
+
+	/*
+	 * This is necessary, because some filesystems (e.g. ext3) lock
+	 * mutexes in their .freeze_fs() callbacks and leave them locked for
+	 * their .unfreeze_fs() callbacks to unlock.  This is done under
+	 * bdev->bd_fsfreeze_mutex, which is then released, but it makes
+	 * lockdep think something may be wrong when freeze_bdev() attempts
+	 * to acquire bdev->bd_fsfreeze_mutex for the next filesystem.
+	 */
+	lockdep_off();