ocfs2: fix circular locking dependency in ocfs2_init_acl()

A lockdep warning indicates a circular locking dependency between
`&oi->ip_xattr_sem` and `&journal->j_trans_barrier`:

WARNING: possible circular locking dependency detected
is trying to acquire lock:
 (&oi->ip_xattr_sem){++++}-{4:4}, at: ocfs2_init_acl+0x2fd/0x7e0
 fs/ocfs2/acl.c:367

but task is already holding lock:
 (&journal->j_trans_barrier){.+.+}-{4:4}, at: ocfs2_start_trans+0x3ab/0x700
 fs/ocfs2/journal.c:369

The deadlock involves two code paths: Path 1 (setxattr) where
`ocfs2_xattr_set()` acquires `ip_xattr_sem` (write) and then starts a
transaction, which acquires `j_trans_barrier` (read); and Path 2
(mkdir/mknod) where `ocfs2_mknod()` starts a transaction (`j_trans_barrier`
read) and then calls `ocfs2_init_acl()`, which attempts to acquire
`ip_xattr_sem` (read) on the parent directory to retrieve the default ACL.

Because rw_semaphores are subject to writer priority, a pending writer on
`j_trans_barrier` (e.g., the journal commit thread) can cause Path 1 to
block, while Path 2 is blocked waiting for Path 1 to release
`ip_xattr_sem`.

The patch fixes the lock ordering by precomputing the ACL state before
starting the OCFS2 transaction, while preserving POSIX ACL storage
semantics and the existing inode/security initialization order. By reading
the parent directory's default ACL and preparing the new inode's ACLs
outside the transaction, `ip_xattr_sem` is always acquired before
`j_trans_barrier`.

`struct ocfs2_acl_state` encapsulates the prepared ACL state, while
`ocfs2_acl_init_prepare()` and `ocfs2_acl_init_release()` avoid code
duplication between `ocfs2_mknod()` and `ocfs2_init_security_and_acl()`.
`ocfs2_calc_xattr_init()` and `ocfs2_init_acl()` use this precomputed
state, removing internal `ip_xattr_sem` acquisition and redundant disk
reads.

Additionally, remove the `ip_xattr_sem` acquisition from
`ocfs2_xattr_set_handle()`. This function is only used while initializing a
new inode that has not yet been inserted into the inode hash or attached to
a dentry, meaning there is no risk of concurrent access and the lock is
unnecessary.

Link: https://lore.kernel.org/4094de06-9b69-4174-b2ee-08126dffc693@mail.kernel.org
Fixes: 16c8d569f570 ("ocfs2/acl: use 'ip_xattr_sem' to protect getting extended attribute")
Signed-off-by: Krystian Kaniewski <krystianmkaniewski@gmail.com>
Assisted-by: Gemini:gemini-3.5-flash Gemini:gemini-3.1-pro-preview syzbot
Reported-by: syzbot+4007ab5229e732466d9f@syzkaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=4007ab5229e732466d9f
Link: https://syzkaller.appspot.com/ai_job?id=cc75363d-c672-499e-8fc5-44bcdc1cee39
Reviewed-by: Joseph Qi <joseph.qi@linux.alibaba.com>
Cc: Mark Fasheh <mark@fasheh.com>
Cc: Joel Becker <jlbec@evilplan.org>
Cc: Junxiao Bi <junxiao.bi@oracle.com>
Cc: Changwei Ge <gechangwei@live.cn>
Cc: Jun Piao <piaojun@huawei.com>
Cc: Heming Zhao <heming.zhao@suse.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

0 files changed, 0 insertions, 0 deletions