Fast commit can hold s_fc_lock while writing journal blocks. Mapping the journal inode can take its i_data_sem. Normal inode update paths can take a data inode i_data_sem and then s_fc_lock, which makes lockdep report a circular dependency.
lockdep treats all i_data_sem instances as one lock class and cannot distinguish the journal inode i_data_sem from a regular inode i_data_sem. The journal inode is not tracked by fast commit and no FC waiters ever depend on it, so this is not a real ABBA deadlock. Assign the journal inode a dedicated i_data_sem lockdep subclass to avoid the false positive. Inode cache objects can be recycled, so also reset i_data_sem to I_DATA_SEM_NORMAL when allocating an ext4 inode. Otherwise a new inode may inherit an old subclass (journal/quota/ea) and trigger lockdep warnings. Signed-off-by: Li Chen <[email protected]> --- fs/ext4/ext4.h | 4 +++- fs/ext4/super.c | 8 ++++++++ 2 files changed, 11 insertions(+), 1 deletion(-) diff --git a/fs/ext4/ext4.h b/fs/ext4/ext4.h index bd30c24d4f948..2e1681057196a 100644 --- a/fs/ext4/ext4.h +++ b/fs/ext4/ext4.h @@ -1025,12 +1025,14 @@ do { \ * than the first * I_DATA_SEM_QUOTA - Used for quota inodes only * I_DATA_SEM_EA - Used for ea_inodes only + * I_DATA_SEM_JOURNAL - Used for journal inode only */ enum { I_DATA_SEM_NORMAL = 0, I_DATA_SEM_OTHER, I_DATA_SEM_QUOTA, - I_DATA_SEM_EA + I_DATA_SEM_EA, + I_DATA_SEM_JOURNAL }; struct ext4_fc_inode_snap; diff --git a/fs/ext4/super.c b/fs/ext4/super.c index 79762c3e0dff3..4f5f0c21d436f 100644 --- a/fs/ext4/super.c +++ b/fs/ext4/super.c @@ -1423,6 +1423,9 @@ static struct inode *ext4_alloc_inode(struct super_block *sb) INIT_WORK(&ei->i_rsv_conversion_work, ext4_end_io_rsv_work); ext4_fc_init_inode(&ei->vfs_inode); spin_lock_init(&ei->i_fc_lock); +#ifdef CONFIG_LOCKDEP + lockdep_set_subclass(&ei->i_data_sem, I_DATA_SEM_NORMAL); +#endif return &ei->vfs_inode; } @@ -5863,6 +5866,11 @@ static struct inode *ext4_get_journal_inode(struct super_block *sb, return ERR_PTR(-EFSCORRUPTED); } +#ifdef CONFIG_LOCKDEP + lockdep_set_subclass(&EXT4_I(journal_inode)->i_data_sem, + I_DATA_SEM_JOURNAL); +#endif + ext4_debug("Journal inode found at %p: %lld bytes\n", journal_inode, journal_inode->i_size); return journal_inode; -- 2.53.0
