linux-kernel - [PATCH 2/2] ecryptfs: Release lower parent dentry after creating dir

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Message-ID: <20251223194153.2818445-3-code@tyhicks.com>
Date: Tue, 23 Dec 2025 13:41:53 -0600
From: Tyler Hicks <code@...icks.com>
To: NeilBrown <neil@...wn.name>,
	Christian Brauner <brauner@...nel.org>,
	Jeff Layton <jlayton@...nel.org>,
	Amir Goldstein <amir73il@...il.com>
Cc: ecryptfs@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: [PATCH 2/2] ecryptfs: Release lower parent dentry after creating dir

Fix a mkdir-induced usage count imbalance that tripped a umount_check()
BUG while unmounting the lower filesystem. Commit f046fbb4d81d
("ecryptfs: use new start_creating/start_removing APIs") added a new
dget() of the lower parent dir, in ecryptfs_mkdir(), but did not dput()
the dentry before returning from that function.

The BUG output as seen while running the eCryptfs test suite:

$ ./run_tests.sh -b 131072 -c safe,destructive -f ext4 -K -t lp-926292.sh
...
Running eCryptfs filesystem tests on ext4
lp-926292
------------[ cut here ]------------
BUG: Dentry ffff8e6692d11988{i=c,n=ECRYPTFS_FNEK_ENCRYPTED.FXZuRGZL7QAFtER.JeA46DtdKqkkQx9H2Vpmv234J5CU8YSsrUwZJK4AbXbrN5WkZ348wnqstovKKxA-}  still in use (1) [unmount of ext4 loop0]
WARNING: CPU: 7 PID: 950 at fs/dcache.c:1590 umount_check+0x5e/0x80
Modules linked in: md5 libmd5 ecryptfs encrypted_keys ext4 crc16 mbcache jbd2
CPU: 7 UID: 0 PID: 950 Comm: umount Not tainted 6.18.0-rc1-00013-gf046fbb4d81d #17 PREEMPT(full)
Hardware name: Bochs Bochs, BIOS Bochs 01/01/2011
RIP: 0010:umount_check+0x5e/0x80
Code: 88 38 06 00 00 48 8b 40 28 4c 8b 08 48 8b 46 68 48 85 c0 74 04 48 8b 50 38 51 48 c7 c7 60 32 9c b5 48 89 f1 e8 43 5e ca ff 90 <0f> 0b 90 90 58 31 c0 e9 46 9d 6c 00 41 83 f8 01 75 b8 eb a3 66 66
RSP: 0018:ffffa19940c4bdd0 EFLAGS: 00010282
RAX: 0000000000000000 RBX: ffff8e6692fad4c0 RCX: 0000000000000000
RDX: 0000000000000004 RSI: ffffa19940c4bc70 RDI: 00000000ffffffff
RBP: ffffffffb4eb5930 R08: 00000000ffffdfff R09: 0000000000000001
R10: 00000000ffffdfff R11: ffffffffb5c8a9e0 R12: ffff8e6692fad4c0
R13: ffff8e6692fad4c0 R14: ffff8e6692d11a40 R15: ffff8e6692d11988
FS:  00007f6b4b491800(0000) GS:ffff8e670506e000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007f6b4b5f8d40 CR3: 0000000114eb7001 CR4: 0000000000772ef0
PKRU: 55555554
Call Trace:
 <TASK>
 d_walk+0xfd/0x370
 shrink_dcache_for_umount+0x4d/0x140
 generic_shutdown_super+0x20/0x160
 kill_block_super+0x1a/0x40
 ext4_kill_sb+0x22/0x40 [ext4]
 deactivate_locked_super+0x33/0xa0
 cleanup_mnt+0xba/0x150
 task_work_run+0x5c/0xa0
 exit_to_user_mode_loop+0xac/0xb0
 do_syscall_64+0x2ab/0xfa0
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f6b4b6c2a2b
Code: c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 40 00 f3 0f 1e fa 31 f6 e9 05 00 00 00 0f 1f 44 00 00 f3 0f 1e fa b8 a6 00 00 00 0f 05 <48> 3d 00 f0 ff ff 77 05 c3 0f 1f 40 00 48 8b 15 b9 83 0d 00 f7 d8
RSP: 002b:00007ffcd5b8b498 EFLAGS: 00000246 ORIG_RAX: 00000000000000a6
RAX: 0000000000000000 RBX: 000055b84af0b9e0 RCX: 00007f6b4b6c2a2b
RDX: 0000000000000000 RSI: 0000000000000000 RDI: 000055b84af0bdf0
RBP: 00007ffcd5b8b570 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000103 R11: 0000000000000246 R12: 000055b84af0bae0
R13: 0000000000000000 R14: 000055b84af0bdf0 R15: 0000000000000000
 </TASK>
---[ end trace 0000000000000000 ]---
EXT4-fs (loop0): unmounting filesystem 00d9ea41-f61e-43d0-a449-6be03e7e8428.
EXT4-fs (loop0): sb orphan head is 12
sb_info orphan list:
  inode loop0:12 at ffff8e66950e1df0: mode 40700, nlink 0, next 0
Assertion failure in ext4_put_super() at fs/ext4/super.c:1345: 'list_empty(&sbi->s_orphan)'

Fixes: f046fbb4d81d ("ecryptfs: use new start_creating/start_removing APIs")
Signed-off-by: Tyler Hicks <code@...icks.com>
---
 fs/ecryptfs/inode.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/fs/ecryptfs/inode.c b/fs/ecryptfs/inode.c
index e73d9de676a6..8ab014db3e03 100644
--- a/fs/ecryptfs/inode.c
+++ b/fs/ecryptfs/inode.c
@@ -533,6 +533,7 @@ static struct dentry *ecryptfs_mkdir(struct mnt_idmap *idmap, struct inode *dir,
 	fsstack_copy_inode_size(dir, lower_dir);
 	set_nlink(dir, lower_dir->i_nlink);
 out:
+	dput(lower_dir_dentry);
 	end_creating(lower_dentry);
 	if (d_really_is_negative(dentry))
 		d_drop(dentry);
-- 
2.43.0