ext4: introduce ext4_put_ea_inode() for safe deferred iput

Calling iput() on EA inodes while holding xattr_sem or a jbd2 handle
can trigger write_inode_now() -> ext4_writepages() -> s_writepages_rwsem,
creating a lock ordering issue during mount (!SB_ACTIVE).

Add ext4_put_ea_inode() which uses iput_if_not_last() as a fast path.
If this is not the last reference, it is dropped immediately.  If this
is the last reference, the inode is linked onto a per-sb lock-free llist
via i_ea_iput_node (embedded in ext4_inode_info, sharing space with the
unused xattr_sem of EA inodes via a union) and a delayed worker
(1 jiffie) performs the final iput() in a clean context.  This avoids
per-iput memory allocation.

Flush points ensure all pending EA inode evictions complete before
dependent resources become unavailable:
- ext4_put_super / failed_mount9: before quota shutdown
- failed_mount_wq: before freeing xattr caches
- failed_mount3a: before freeing shrinker (journal replay case)
- ext4_sync_fs: before remount-ro, freeze, or sync completes

Initialization is placed before journal loading since fast commit
replay may trigger evictions that call ext4_put_ea_inode().

Also moves init_rwsem(xattr_sem) from init_once to ext4_alloc_inode to
handle slab object reuse after the union field has been overwritten.

Signed-off-by: Yun Zhou <yun.zhou@windriver.com>
Suggested-by: Jan Kara <jack@suse.cz>
Reviewed-by: Jan Kara <jack@suse.cz>
Link: https://patch.msgid.link/20260710030851.2791589-3-yun.zhou@windriver.com
Signed-off-by: Theodore Ts'o <tytso@mit.edu>

0 files changed, 0 insertions, 0 deletions