PM: suspend: clean up redundant filesystems_freeze/thaw() handling

The recently introduced support for freezing filesystems during system
suspend included calls to filesystems_freeze() in both suspend_prepare()
and enter_state(), as well as calls to filesystems_thaw() in both
suspend_finish() and the Unlock path in enter_state(). These are
redundant.

Moreover, calling filesystems_freeze() twice, from both suspend_prepare()
and enter_state(), leads to a black screen and makes the system unable
to resume in some cases.

Address this as follows:

 - filesystems_freeze() is already called in suspend_prepare(), which
   is the proper and consistent place to handle pre-suspend operations.
   The second call in enter_state() is unnecessary and so remove it.

 - filesystems_thaw() is invoked in suspend_finish(), which covers
   successful suspend/resume paths. In the failure case, add a call
   to filesystems_thaw() only when needed, avoiding the duplicate call
   in the general Unlock path.

This change simplifies the suspend code and avoids repeated freeze/thaw
calls, while preserving correct ordering and behavior.

Fixes: eacfbf7 ("power: freeze filesystems during suspend/resume")
Signed-off-by: Zihuan Zhang <zhangzihuan@kylinos.cn>
Link: https://patch.msgid.link/20250712030824.81474-1-zhangzihuan@kylinos.cn
[ rjw: Changelog edits ]
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

Author: Zihuan Zhang

kernel/power/suspend.c

@@ -384,6 +384,7 @@ static int suspend_prepare(suspend_state_t state)
 		return 0;
 
 	dpm_save_failed_step(SUSPEND_FREEZE);
+	filesystems_thaw();
 	pm_notifier_call_chain(PM_POST_SUSPEND);
  Restore:
 	pm_restore_console();
@@ -592,8 +593,6 @@ static int enter_state(suspend_state_t state)
 		ksys_sync_helper();
 		trace_suspend_resume(TPS("sync_filesystems"), 0, false);
 	}
-	if (filesystem_freeze_enabled)
-		filesystems_freeze();
 
 	pm_pr_dbg("Preparing system for sleep (%s)\n", mem_sleep_labels[state]);
 	pm_suspend_clear_flags();
@@ -613,7 +612,6 @@ static int enter_state(suspend_state_t state)
 	pm_pr_dbg("Finishing wakeup.\n");
 	suspend_finish();
  Unlock:
-	filesystems_thaw();
 	mutex_unlock(&system_transition_mutex);
 	return error;
 }