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Subject: Re: [PATCH 3/3] hfs: add lock nesting notation to hfs_find_init
From:   Viacheslav Dubeyko <slava@dubeyko.com>
In-Reply-To: <20210629144803.62541-4-desmondcheongzx@gmail.com>
Date:   Tue, 29 Jun 2021 12:33:46 -0700
Cc:     gustavoars@kernel.org, viro@zeniv.linux.org.uk,
        linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org,
        skhan@linuxfoundation.org, gregkh@linuxfoundation.org,
        linux-kernel-mentees@lists.linuxfoundation.org,
        syzbot+b718ec84a87b7e73ade4@syzkaller.appspotmail.com
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Message-Id: <763B3E9F-1D48-4D0E-830C-8260D2329627@dubeyko.com>
References: <20210629144803.62541-1-desmondcheongzx@gmail.com>
 <20210629144803.62541-4-desmondcheongzx@gmail.com>
To:     Desmond Cheong Zhi Xi <desmondcheongzx@gmail.com>
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> On Jun 29, 2021, at 7:48 AM, Desmond Cheong Zhi Xi =
<desmondcheongzx@gmail.com> wrote:
>=20
> Syzbot reports a possible recursive lock:
> =
https://syzkaller.appspot.com/bug?id=3Df007ef1d7a31a469e3be7aeb0fde0769b18=
585db
>=20
> This happens due to missing lock nesting information. =46rom the logs,
> we see that a call to hfs_fill_super is made to mount the hfs
> filesystem. While searching for the root inode, the lock on the
> catalog btree is grabbed. Then, when the parent of the root isn't
> found, a call to __hfs_bnode_create is made to create the parent of
> the root. This eventually leads to a call to hfs_ext_read_extent which
> grabs a lock on the extents btree.
>=20
> Since the order of locking is catalog btree -> extents btree, this
> lock hierarchy does not lead to a deadlock.
>=20
> To tell lockdep that this locking is safe, we add nesting notation to
> distinguish between catalog btrees, extents btrees, and attributes
> btrees (for HFS+). This has already been done in hfsplus.
>=20
> Reported-and-tested-by: =
syzbot+b718ec84a87b7e73ade4@syzkaller.appspotmail.com
> Signed-off-by: Desmond Cheong Zhi Xi <desmondcheongzx@gmail.com>
> ---
> fs/hfs/bfind.c | 14 +++++++++++++-
> fs/hfs/btree.h |  7 +++++++
> 2 files changed, 20 insertions(+), 1 deletion(-)
>=20
> diff --git a/fs/hfs/bfind.c b/fs/hfs/bfind.c
> index 4af318fbda77..ef9498a6e88a 100644
> --- a/fs/hfs/bfind.c
> +++ b/fs/hfs/bfind.c
> @@ -25,7 +25,19 @@ int hfs_find_init(struct hfs_btree *tree, struct =
hfs_find_data *fd)
> 	fd->key =3D ptr + tree->max_key_len + 2;
> 	hfs_dbg(BNODE_REFS, "find_init: %d (%p)\n",
> 		tree->cnid, __builtin_return_address(0));
> -	mutex_lock(&tree->tree_lock);
> +	switch (tree->cnid) {
> +	case HFS_CAT_CNID:
> +		mutex_lock_nested(&tree->tree_lock, =
CATALOG_BTREE_MUTEX);
> +		break;
> +	case HFS_EXT_CNID:
> +		mutex_lock_nested(&tree->tree_lock, =
EXTENTS_BTREE_MUTEX);
> +		break;
> +	case HFS_ATTR_CNID:
> +		mutex_lock_nested(&tree->tree_lock, ATTR_BTREE_MUTEX);
> +		break;
> +	default:
> +		return -EINVAL;
> +	}
> 	return 0;
> }
>=20
> diff --git a/fs/hfs/btree.h b/fs/hfs/btree.h
> index 4ba45caf5939..0e6baee93245 100644
> --- a/fs/hfs/btree.h
> +++ b/fs/hfs/btree.h
> @@ -13,6 +13,13 @@ typedef int (*btree_keycmp)(const btree_key *, =
const btree_key *);
>=20
> #define NODE_HASH_SIZE  256
>=20
> +/* B-tree mutex nested subclasses */
> +enum hfs_btree_mutex_classes {
> +	CATALOG_BTREE_MUTEX,
> +	EXTENTS_BTREE_MUTEX,
> +	ATTR_BTREE_MUTEX,
> +};
> +
> /* A HFS BTree held in memory */
> struct hfs_btree {
> 	struct super_block *sb;
> --=20
> 2.25.1
>=20

Looks good to me.

Reviewed-by: Viacheslav Dubeyko <slava@dubeyko.com>

Thanks,
Slava.