From: Ritesh Harjani <riteshh@linux.ibm.com>
Subject: [PATCH] ext4: Unregister sysfs path before destroying jbd2 journal
Patch-mainline: v5.7-rc1
Git-commit: 5e47868fb94b63c7068dcfd2469d99fba06bae9d
References: bsc#1167338 bsc#1167288

Call ext4_unregister_sysfs(), before destroying jbd2 journal,
since below might cause, NULL pointer dereference issue.
This got reported with LTP tests.

ext4_put_super() 		cat /sys/fs/ext4/loop2/journal_task
	| 				ext4_attr_show();
ext4_jbd2_journal_destroy();  			|
    	|				 journal_task_show()
	| 					|
	| 				task_pid_vnr(NULL);
sbi->s_journal = NULL;

Signed-off-by: Ritesh Harjani <riteshh@linux.ibm.com>
Acked-by: Jan Kara <jack@suse.cz>
---
 fs/ext4/super.c |    8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

--- a/fs/ext4/super.c
+++ b/fs/ext4/super.c
@@ -982,6 +982,13 @@ static void ext4_put_super(struct super_
 
 	destroy_workqueue(sbi->rsv_conversion_wq);
 
+	/*
+	 * Unregister sysfs before destroying jbd2 journal.
+	 * Since we could still access attr_journal_task attribute via sysfs
+	 * path which could have sbi->s_journal->j_task as NULL
+	 */
+	ext4_unregister_sysfs(sb);
+
 	if (sbi->s_journal) {
 		aborted = is_journal_aborted(sbi->s_journal);
 		err = jbd2_journal_destroy(sbi->s_journal);
@@ -990,7 +997,6 @@ static void ext4_put_super(struct super_
 			ext4_abort(sb, "Couldn't clean up the journal");
 	}
 
-	ext4_unregister_sysfs(sb);
 	ext4_es_unregister_shrinker(sbi);
 	del_timer_sync(&sbi->s_err_report);
 	ext4_release_system_zone(sb);