[LU-11813] pdirops lh_hbits is not initialized

• Type: Bug
• Resolution: Unresolved
• Priority: Minor
• Labels: ldiskfs performance
• Severity: 3
• Assignee: WC Triage
• Reporter: Andreas Dilger

Description

I was reading through the pdirops patch and noticed that the lh_hbits field in the ldiskfs pdirops patch is not initialized correctly. This indirectly results in the "major" hash of the filename to always be zero, and the full 32-bit hash value is stored in the minor version of the hash. It isn't clear what impact this error would have on performance.

enum {
       HTREE_HBITS_MIN         = 2,
       HTREE_HBITS_DEF         = 14,
       HTREE_HBITS_MAX         = 32,
};

struct htree_lock_head *
htree_lock_head_alloc(unsigned depth, unsigned hbits, unsigned priv)
{
       :
       lhead = kzalloc(offsetof(struct htree_lock_head,
                                lh_children[depth]) + priv, GFP_NOFS);
       if (lhead == NULL)
               return NULL;

       if (hbits < HTREE_HBITS_MIN)
               lhead->lh_hbits = HTREE_HBITS_MIN;
       else if (hbits > HTREE_HBITS_MAX)
               lhead->lh_hbits = HTREE_HBITS_MAX;
       :
}

struct htree_lock_head *ext4_htree_lock_head_alloc(unsigned hbits)
{
       struct htree_lock_head *lhead;

       lhead = htree_lock_head_alloc(EXT4_LK_MAX, hbits, 0);
       if (lhead != NULL) {
               htree_lock_event_attach(lhead, EXT4_LK_SPIN, HTREE_EVENT_WR,
                                       ext4_htree_event_cb);
       }
       return lhead;
}

static int htree_node_lock_internal()
{
       :
       key = hash_long(key, lhead->lh_hbits);

       mi_bits = lhead->lh_hbits >> 1;
       ma_bits = lhead->lh_hbits - mi_bits;

       lck->lk_nodes[dep].ln_major_key = major = key & ((1U << ma_bits) - 1);
       lck->lk_nodes[dep].ln_minor_key = minor = key >> ma_bits;
       :
}

struct htree_lock_head *ldiskfs_htree_lock_head_alloc(unsigned hbits)
{               
        return htree_lock_head_alloc(LDISKFS_LK_MAX, hbits, 0);
}

        obj->oo_hl_head = ldiskfs_htree_lock_head_alloc(HTREE_HBITS_DEF);