[PATCH v2] ntfs: fail attrlist updates when the superblock is inactive

[Peiyang He]

generic_shutdown_super() clears SB_ACTIVE before evicting cached inodes.
If eviction selects the fake inode for a base inode's unnamed
$ATTRIBUTE_LIST attribute, ntfs_evict_big_inode() drops the fake inode's
reference on the base inode while the fake inode is still hashed and marked
I_FREEING.

That iput can synchronously write back the base inode. The writeback path
may update mapping pairs and call ntfs_attrlist_update(), which
unconditionally calls ntfs_attr_iget() for the same $ATTRIBUTE_LIST fake
inode. VFS then finds the I_FREEING inode and waits for eviction to finish,
but the current task is still inside that eviction path, causing a
self-deadlock in find_inode().

Fix this by mirroring the teardown guard used by __ntfs_write_inode():
once SB_ACTIVE has been cleared, do not try to iget the attribute-list fake inode.
Return -EIO so teardown aborts the update instead of waiting on the inode it is evicting.

Reported-by: Peiyang He <peiyang_he@xxxxxxxxxxxxxxxx>
Closes: https://lore.kernel.org/all/AB8D5E603E6EA856+ae5f622a-dd3a-4e38-bdd2-42276ae0e1a8@xxxxxxxxxxxxxxxx/
Fixes: 495e90fa3348 ("ntfs: update attrib operations")
Cc: stable@xxxxxxxxxxxxxxx
Signed-off-by: Peiyang He <peiyang_he@xxxxxxxxxxxxxxxx>
Assisted-by: Codex:gpt-5.5
Reviewed-by: Hyunchul Lee <hyc.lee@xxxxxxxxx>
---
Changes in v2:
  - add code comments
  - collect Reviewed-by

 fs/ntfs/attrlist.c | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/fs/ntfs/attrlist.c b/fs/ntfs/attrlist.c
index afb13038ba42..be3086d34338 100644
--- a/fs/ntfs/attrlist.c
+++ b/fs/ntfs/attrlist.c
@@ -57,6 +57,15 @@ int ntfs_attrlist_update(struct ntfs_inode *base_ni)
 	struct ntfs_inode *attr_ni;
 	int err;
 
+	/*
+	 * generic_shutdown_super() clears SB_ACTIVE before evicting cached
+	 * inodes. Do not look up the attribute-list inode after SB_ACTIVE has
+	 * been cleared; it may already be I_FREEING, and waiting on it can
+	 * self-deadlock.
+	 */
+	if (!(VFS_I(base_ni)->i_sb->s_flags & SB_ACTIVE))
+		return -EIO;
+
 	attr_vi = ntfs_attr_iget(VFS_I(base_ni), AT_ATTRIBUTE_LIST, AT_UNNAMED, 0);
 	if (IS_ERR(attr_vi)) {
 		err = PTR_ERR(attr_vi);

base-commit: 1a3746ccbb0a97bed3c06ccde6b880013b1dddc1
-- 
2.43.0