Re: [PATCH] ocfs2: fix deadlock in dio write orphan cleanup path

[sashiko-bot@kernel.org]

Thank you for your contribution! Sashiko AI review found 3 potential issue(s) to consider:

Pre-existing issues:
- [High] The patch completely fails to resolve the AB-BA deadlock between the write path and the orphan recovery path, as the exact same lock dependency is immediately recreated.
- [High] The identical lock dependency cycle (A -> B -> D) exists unmitigated in the orphan addition path.
- [High] Directory `i_rwsem` operations use the wrong subclass, violating VFS lock ordering rules and hiding parent-child deadlocks.
--

commit a3ea3ef9d81bdb971acfa026b14e772f33af54fa
Author: Deepanshu Kartikey <kartikey406@gmail.com>

ocfs2: fix deadlock in dio write orphan cleanup path

This commit attempts to fix an AB-BA deadlock in the direct IO orphan cleanup
path by releasing the file's cluster lock before calling
ocfs2_del_inode_from_orphan(). It passes NULL for di_bh to signal the
function to acquire its own lock.

Closes: https://syzkaller.appspot.com/bug?extid=ce129763ce7d7e914739

> diff --git a/fs/ocfs2/aops.c b/fs/ocfs2/aops.c
> index 6ec198bdab121..095cb3e44c65e 100644
> --- a/fs/ocfs2/aops.c
> +++ b/fs/ocfs2/aops.c

[ ... ]

> @@ -2371,17 +2372,25 @@ static int ocfs2_dio_end_io_write(struct inode *inode,
>  		ocfs2_commit_trans(osb, handle);
>  unlock:
>  	up_write(&oi->ip_alloc_sem);
> +	/*
> +	 * Release the cluster lock and di_bh BEFORE calling
> +	 * ocfs2_del_inode_from_orphan(). That function will acquire
> +	 * inode_lock(orphan_dir_inode) which would cause an AB-BA
> +	 *  deadlock with recovery paths that hold orphan_dir lock
> +	 * before acquiring the file inode lock.
> +	 */
> +	orphaned = (!ret && dwc->dw_orphaned);
> +	ocfs2_inode_unlock(inode, 1);
> +	brelse(di_bh);
> +	di_bh = NULL;
>  
> -	/* everything looks good, let's start the cleanup */
> -	if (!ret && dwc->dw_orphaned) {
> +	/* everything looks good, let's start the orphan cleanup */
> +	if (orphaned) {
>  		BUG_ON(dwc->dw_writer_pid != task_pid_nr(current));
> -
> -		ret = ocfs2_del_inode_from_orphan(osb, inode, di_bh, 0, 0);
> +		ret = ocfs2_del_inode_from_orphan(osb, inode, NULL, 0, 0);
>  		if (ret < 0)
>  			mlog_errno(ret);
>  	}
> -	ocfs2_inode_unlock(inode, 1);
> -	brelse(di_bh);
>  out:

[ ... ]

> diff --git a/fs/ocfs2/namei.c b/fs/ocfs2/namei.c
> index 1277666c77cd2..25bbe2a9776ef 100644
> --- a/fs/ocfs2/namei.c
> +++ b/fs/ocfs2/namei.c
> @@ -2712,10 +2712,21 @@ int ocfs2_del_inode_from_orphan(struct ocfs2_super *osb,
>  {
>  	struct inode *orphan_dir_inode = NULL;
>  	struct buffer_head *orphan_dir_bh = NULL;
> -	struct ocfs2_dinode *di = (struct ocfs2_dinode *)di_bh->b_data;
> +	struct ocfs2_dinode *di;
>  	handle_t *handle = NULL;
>  	int status = 0;
> +	struct buffer_head *local_di_bh = NULL;
>  
> +	if (!di_bh) {
> +		status = ocfs2_inode_lock(inode, &local_di_bh, 1);

[Severity: High]
This is a pre-existing issue, but is the AB-BA deadlock between the write
path and the orphan recovery path truly resolved?

When di_bh is NULL, this immediately reacquires the exact same
ocfs2_inode_lock on the file inode (Lock B) before the orphan directory's
VFS lock (Lock D) is acquired later in this function:

fs/ocfs2/namei.c:ocfs2_del_inode_from_orphan() {
    ...
    inode_lock(orphan_dir_inode);
    ...
}

Since the lock acquisition order remains exactly the same (B -> D) as it
was before the patch, and the recovery path acquires these locks in the
reverse order (D -> B), doesn't the deadlock cycle remain unmitigated?

Also, as a related pre-existing issue, couldn't the identical lock
dependency cycle (A -> B -> D) still occur unmitigated in the orphan
addition path?

During direct IO writes, ocfs2_dio_get_block() calls
ocfs2_add_inode_to_orphan() while holding the file's VFS lock (Lock A).
Inside ocfs2_add_inode_to_orphan(), the file's cluster lock (Lock B) is
acquired:

fs/ocfs2/namei.c:ocfs2_add_inode_to_orphan() {
    status = ocfs2_inode_lock(inode, &di_bh, 1);
    ...
    status = ocfs2_prepare_orphan_dir(osb, &orphan_dir_inode,
                                      OCFS2_I(inode)->ip_blkno,
                                      orphan_name,
                                      &orphan_insert,
                                      true);
}

This calls ocfs2_prepare_orphan_dir(), which acquires the orphan
directory's VFS lock (Lock D) via inode_lock(). This seems to establish
the exact same A -> B -> D deadlock cycle against the recovery path.

Finally, this is a pre-existing issue, but might the use of inode_lock()
on the orphan directory violate VFS lock ordering rules?

When modifying a directory, the VFS requires acquiring the directory's
i_rwsem with subclass I_MUTEX_PARENT. In ocfs2_del_inode_from_orphan()
and ocfs2_lookup_lock_orphan_dir(), the default inode_lock() is used
instead:

fs/ocfs2/namei.c:ocfs2_del_inode_from_orphan() {
    ...
    inode_lock(orphan_dir_inode);
    ...
}

Because the caller already holds the file's inode_lock (also subclass 0),
acquiring the orphan directory's lock using subclass 0 can create a
lockdep AA self-deadlock or cycle warning. Furthermore, taking a child's
lock before its parent directory's lock intrinsically violates the VFS
hierarchy (I_MUTEX_PARENT -> I_MUTEX_NORMAL). Should this be using
inode_lock_nested(..., I_MUTEX_PARENT) instead?

> +		if (status < 0) {
> +			mlog_errno(status);
> +			return status;
> +		}
> +		di_bh = local_di_bh;
> +	}
> +
> +	di = (struct ocfs2_dinode *)di_bh->b_data;
>  	orphan_dir_inode = ocfs2_get_system_file_inode(osb,
>  			ORPHAN_DIR_SYSTEM_INODE,
>  			le16_to_cpu(di->i_dio_orphaned_slot));

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/20260620080802.35165-1-kartikey406@gmail.com?part=1