[RFC PATCH 4/4] vfs: add filesystem freeze/thaw callbacks for power management

[James Bottomley <James.Bottomley@HansenPartnership.com>]

Introduce a freeze function, which iterates superblocks in reverse
order freezing filesystems.  The indicator a filesystem is freezable
is either possessing a s_bdev or a freeze_super method.  So this can
be used in efivarfs, whether the freeze is for hibernate is also
passed in via the new FREEZE_FOR_HIBERNATE flag.

Thawing is done opposite to freezing (so superblock traversal in
regular order) and the whole thing is plumbed into power management.
The original ksys_sync() is preserved so the whole freezing step is
optional (if it fails we're no worse off than we are today) so it
doesn't inhibit suspend/hibernate if there's a failure.

Signed-off-by: James Bottomley <James.Bottomley@HansenPartnership.com>
---
 fs/super.c               | 61 ++++++++++++++++++++++++++++++++++++++++
 include/linux/fs.h       |  5 ++++
 kernel/power/hibernate.c | 12 ++++++++
 kernel/power/suspend.c   |  4 +++
 4 files changed, 82 insertions(+)

diff --git a/fs/super.c b/fs/super.c
index 76785509d906..b4b0986414b0 100644
--- a/fs/super.c
+++ b/fs/super.c
@@ -1461,6 +1461,67 @@ static struct super_block *get_bdev_super(struct block_device *bdev)
 	return sb;
 }
 
+/*
+ * Kernel freezing and thawing is only done in the power management
+ * subsystem and is thus single threaded (so we don't have to worry
+ * here about multiple calls to filesystems_freeze/thaw().
+ */
+
+static int freeze_flags;
+
+static void filesystems_freeze_callback(struct super_block *sb)
+{
+	/* errors don't fail suspend so ignore them */
+	if (sb->s_op->freeze_super)
+		sb->s_op->freeze_super(sb, FREEZE_MAY_NEST
+				       | FREEZE_HOLDER_KERNEL
+				       | freeze_flags);
+	else if (sb->s_bdev)
+		freeze_super(sb, FREEZE_MAY_NEST | FREEZE_HOLDER_KERNEL
+			     | freeze_flags);
+	else {
+		pr_info("Ignoring filesystem %s\n", sb->s_type->name);
+		return;
+	}
+
+	pr_info("frozen %s, now syncing block ...", sb->s_type->name);
+	sync_blockdev(sb->s_bdev);
+	pr_info("done.");
+}
+
+/**
+ * filesystems_freeze - freeze callback for power management
+ *
+ * Freeze all active filesystems (in reverse superblock order)
+ */
+void filesystems_freeze(bool for_hibernate)
+{
+	freeze_flags = for_hibernate ? FREEZE_FOR_HIBERNATE : 0;
+	__iterate_supers_rev(filesystems_freeze_callback);
+}
+
+static void filesystems_thaw_callback(struct super_block *sb)
+{
+	if (sb->s_op->thaw_super)
+		sb->s_op->thaw_super(sb, FREEZE_MAY_NEST
+				     | FREEZE_HOLDER_KERNEL
+				     | freeze_flags);
+	else if (sb->s_bdev)
+		thaw_super(sb,	FREEZE_MAY_NEST | FREEZE_HOLDER_KERNEL
+			   | freeze_flags);
+}
+
+/**
+ * filesystems_thaw - thaw callback for power management
+ *
+ * Thaw all active filesystems (in forward superblock order)
+ */
+void filesystems_thaw(bool for_hibernate)
+{
+	freeze_flags = for_hibernate ? FREEZE_FOR_HIBERNATE : 0;
+	__iterate_supers(filesystems_thaw_callback);
+}
+
 /**
  * fs_bdev_freeze - freeze owning filesystem of block device
  * @bdev: block device
diff --git a/include/linux/fs.h b/include/linux/fs.h
index cbbb704eff74..de154e9379ec 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -2272,6 +2272,7 @@ extern loff_t vfs_dedupe_file_range_one(struct file *src_file, loff_t src_pos,
  * @FREEZE_HOLDER_KERNEL: kernel wants to freeze or thaw filesystem
  * @FREEZE_HOLDER_USERSPACE: userspace wants to freeze or thaw filesystem
  * @FREEZE_MAY_NEST: whether nesting freeze and thaw requests is allowed
+ * @FREEZE_FOR_HIBERNATE: set if freeze is from power management hibernate
  *
  * Indicate who the owner of the freeze or thaw request is and whether
  * the freeze needs to be exclusive or can nest.
@@ -2285,6 +2286,7 @@ enum freeze_holder {
 	FREEZE_HOLDER_KERNEL	= (1U << 0),
 	FREEZE_HOLDER_USERSPACE	= (1U << 1),
 	FREEZE_MAY_NEST		= (1U << 2),
+	FREEZE_FOR_HIBERNATE	= (1U << 3),
 };
 
 struct super_operations {
@@ -3919,4 +3921,7 @@ static inline bool vfs_empty_path(int dfd, const char __user *path)
 
 int generic_atomic_write_valid(struct kiocb *iocb, struct iov_iter *iter);
 
+void filesystems_freeze(bool for_hibernate);
+void filesystems_thaw(bool for_hibernate);
+
 #endif /* _LINUX_FS_H */
diff --git a/kernel/power/hibernate.c b/kernel/power/hibernate.c
index 10a01af63a80..fc2106e6685a 100644
--- a/kernel/power/hibernate.c
+++ b/kernel/power/hibernate.c
@@ -778,7 +778,12 @@ int hibernate(void)
 
 	ksys_sync_helper();
 
+	pr_info("about to freeze filesystems\n");
+	filesystems_freeze(true);
+	pr_info("filesystem freeze done\n");
+
 	error = freeze_processes();
+	pr_info("process freeze done\n");
 	if (error)
 		goto Exit;
 
@@ -788,7 +793,9 @@ int hibernate(void)
 	if (error)
 		goto Thaw;
 
+	pr_info("About to create snapshot\n");
 	error = hibernation_snapshot(hibernation_mode == HIBERNATION_PLATFORM);
+	pr_info("snapshot done\n");
 	if (error || freezer_test_done)
 		goto Free_bitmaps;
 
@@ -842,6 +849,8 @@ int hibernate(void)
 	}
 	thaw_processes();
 
+	filesystems_thaw(true);
+
 	/* Don't bother checking whether freezer_test_done is true */
 	freezer_test_done = false;
  Exit:
@@ -939,6 +948,8 @@ int hibernate_quiet_exec(int (*func)(void *data), void *data)
 
 	thaw_processes();
 
+	filesystems_thaw(true);
+
 exit:
 	pm_notifier_call_chain(PM_POST_HIBERNATION);
 
@@ -1041,6 +1052,7 @@ static int software_resume(void)
 
 	error = load_image_and_restore();
 	thaw_processes();
+	filesystems_thaw(true);
  Finish:
 	pm_notifier_call_chain(PM_POST_RESTORE);
  Restore:
diff --git a/kernel/power/suspend.c b/kernel/power/suspend.c
index 09f8397bae15..34cc5b0c408c 100644
--- a/kernel/power/suspend.c
+++ b/kernel/power/suspend.c
@@ -544,6 +544,7 @@ int suspend_devices_and_enter(suspend_state_t state)
 static void suspend_finish(void)
 {
 	suspend_thaw_processes();
+	filesystems_thaw(false);
 	pm_notifier_call_chain(PM_POST_SUSPEND);
 	pm_restore_console();
 }
@@ -581,6 +582,7 @@ static int enter_state(suspend_state_t state)
 		trace_suspend_resume(TPS("sync_filesystems"), 0, true);
 		ksys_sync_helper();
 		trace_suspend_resume(TPS("sync_filesystems"), 0, false);
+		filesystems_freeze(false);
 	}
 
 	pm_pr_dbg("Preparing system for sleep (%s)\n", mem_sleep_labels[state]);
@@ -603,6 +605,8 @@ static int enter_state(suspend_state_t state)
 	pm_pr_dbg("Finishing wakeup.\n");
 	suspend_finish();
  Unlock:
+	if (sync_on_suspend_enabled)
+		filesystems_thaw(false);
 	mutex_unlock(&system_transition_mutex);
 	return error;
 }
-- 
2.43.0