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    SubjectRe: [PATCH 3/3] hfs: add lock nesting notation to hfs_find_init
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    > On Jun 29, 2021, at 7:48 AM, Desmond Cheong Zhi Xi <desmondcheongzx@gmail.com> wrote:
    >
    > Syzbot reports a possible recursive lock:
    > https://syzkaller.appspot.com/bug?id=f007ef1d7a31a469e3be7aeb0fde0769b18585db
    >
    > This happens due to missing lock nesting information. From 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.
    >
    > Since the order of locking is catalog btree -> extents btree, this
    > lock hierarchy does not lead to a deadlock.
    >
    > 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.
    >
    > 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(-)
    >
    > 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 = 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;
    > }
    >
    > 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 *);
    >
    > #define NODE_HASH_SIZE 256
    >
    > +/* 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;
    > --
    > 2.25.1
    >

    Looks good to me.

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

    Thanks,
    Slava.


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