[PATCH 09/12] ext4: drop s_umount over opening the log device

Christoph Hellwig
2023-08-02T15:43:33Z

Just like get_tree_bdev needs to drop s_umount when opening the main
device, we need to do the same for the ext4 log device to avoid a
potential lock order reversal with s_unmount for the mark_dead path.

It might be preferable to just drop s_umount over ->fill_super entirely,
but that will require a fairly massive audit first, so we'll do the easy
version here first.

Signed-off-by: Christoph Hellwig <hch@lst.de>
---
fs/ext4/super.c | 3 +++
1 file changed, 3 insertions(+)

diff --git a/fs/ext4/super.c b/fs/ext4/super.c
index 193d665813b611..2ccb19d345c6dd 100644
--- a/fs/ext4/super.c
+++ b/fs/ext4/super.c
@@ -5854,7 +5854,10 @@ static journal_t *ext4_get_dev_journal(struct super_block *sb,
if (WARN_ON_ONCE(!ext4_has_feature_journal(sb)))
return NULL;

+ /* see get_tree_bdev why this is needed and safe */
+ up_write(&sb->s_umount);
bdev = ext4_blkdev_get(j_dev, sb);
+ down_write(&sb->s_umount);
if (bdev == NULL)
return NULL;

--
2.39.2