[PATCH] ext4: unregister extents status shrinker if mount failed

[Alexey Khoroshilov <khoroshilov@ispras.ru>]

If ext4_fill_super() failed after extents status shrinker
has been registered, the shrinker is left in a global list
while the memory, it sits in, is already freed.
Oops is not so bad scenario after that.

Found by Linux File System Verification project (linuxtesting.org).

Signed-off-by: Alexey Khoroshilov <khoroshilov@ispras.ru>
---
 fs/ext4/super.c |    6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/fs/ext4/super.c b/fs/ext4/super.c
index 5d6d5357..5f9cb30 100644
--- a/fs/ext4/super.c
+++ b/fs/ext4/super.c
@@ -3757,7 +3757,7 @@ static int ext4_fill_super(struct super_block *sb, void *data, int silent)
 	if (EXT4_HAS_INCOMPAT_FEATURE(sb, EXT4_FEATURE_INCOMPAT_MMP) &&
 	    !(sb->s_flags & MS_RDONLY))
 		if (ext4_multi_mount_protect(sb, le64_to_cpu(es->s_mmp_block)))
-			goto failed_mount3;
+			goto failed_mount_shr;
 
 	/*
 	 * The first inode we look at is the journal inode.  Don't try
@@ -3766,7 +3766,7 @@ static int ext4_fill_super(struct super_block *sb, void *data, int silent)
 	if (!test_opt(sb, NOLOAD) &&
 	    EXT4_HAS_COMPAT_FEATURE(sb, EXT4_FEATURE_COMPAT_HAS_JOURNAL)) {
 		if (ext4_load_journal(sb, es, journal_devnum))
-			goto failed_mount3;
+			goto failed_mount_shr;
 	} else if (test_opt(sb, NOLOAD) && !(sb->s_flags & MS_RDONLY) &&
 	      EXT4_HAS_INCOMPAT_FEATURE(sb, EXT4_FEATURE_INCOMPAT_RECOVER)) {
 		ext4_msg(sb, KERN_ERR, "required journal recovery "
@@ -4009,6 +4009,8 @@ failed_mount_wq:
 		jbd2_journal_destroy(sbi->s_journal);
 		sbi->s_journal = NULL;
 	}
+failed_mount_shr:
+	ext4_es_unregister_shrinker(sb);
 failed_mount3:
 	del_timer(&sbi->s_err_report);
 	if (sbi->s_flex_groups)
-- 
1.7.9.5