Re: [PATCH v2 1/2] gfs2: fix quota init duplicate scan

Hello,

this is looking good except for one minor detail (see below).

On Tue, Apr 21, 2026 at 10:44 AM Jie Wang <[email protected]> wrote:
> gfs2_quota_init() checks for duplicate quota_change IDs while holding
> qd_lock and the quota hash bucket bitlock. That path used
> gfs2_qd_search_bucket(), which takes a lockref reference via
> lockref_get_not_dead().
>
> On PREEMPT_RT this may sleep, which is not allowed under the bucket
> bitlock, triggering "sleeping function called from invalid context".
>
> Use a no-ref bucket lookup in this path, then continue duplicate
> handling without taking a lockref there.
>
> Refactor gfs2_qd_search_bucket() to build on top of the no-ref helper
> so lookup traversal stays in one place.
>
> This patch fixes a bug reported by syzbot.
>
> Reported-by: [email protected]
> Closes: https://syzkaller.appspot.com/bug?extid=642d0561f78362d67d3f
> Tested-by: [email protected]
> Signed-off-by: Jie Wang <[email protected]>
> ---
>  fs/gfs2/quota.c | 36 +++++++++++++++++++++++++-----------
>  1 file changed, 25 insertions(+), 11 deletions(-)
>
> diff --git a/fs/gfs2/quota.c b/fs/gfs2/quota.c
> index 5290865f27f1..df1cb99c3344 100644
> --- a/fs/gfs2/quota.c
> +++ b/fs/gfs2/quota.c
> @@ -254,9 +254,13 @@ static struct gfs2_quota_data *qd_alloc(unsigned hash, struct gfs2_sbd *sdp, str
>         return NULL;
>  }
>
> -static struct gfs2_quota_data *gfs2_qd_search_bucket(unsigned int hash,
> -                                                    const struct gfs2_sbd *sdp,
> -                                                    struct kqid qid)
> +/*
> + * Lookup variant for callers which already hold qd_lock + bucket lock.
> + */
> +static struct gfs2_quota_data *
> +gfs2_qd_search_bucket_noref(unsigned int hash,
> +                           const struct gfs2_sbd *sdp,
> +                           struct kqid qid)
>  {
>         struct gfs2_quota_data *qd;
>         struct hlist_bl_node *h;
> @@ -264,12 +268,22 @@ static struct gfs2_quota_data *gfs2_qd_search_bucket(unsigned int hash,
>         hlist_bl_for_each_entry_rcu(qd, h, &qd_hash_table[hash], qd_hlist) {
>                 if (!qid_eq(qd->qd_id, qid))
>                         continue;
> -               if (qd->qd_sbd != sdp)
> -                       continue;
> -               if (lockref_get_not_dead(&qd->qd_lockref)) {
> -                       list_lru_del_obj(&gfs2_qd_lru, &qd->qd_lru);
> +               if (qd->qd_sbd == sdp)
>                         return qd;
> -               }
> +       }
> +
> +       return NULL;
> +}
> +
> +static struct gfs2_quota_data *
> +gfs2_qd_search_bucket(unsigned int hash, const struct gfs2_sbd *sdp, struct kqid qid)
> +{
> +       struct gfs2_quota_data *qd;
> +
> +       qd = gfs2_qd_search_bucket_noref(hash, sdp, qid);
> +       if (qd && lockref_get_not_dead(&qd->qd_lockref)) {
> +               list_lru_del_obj(&gfs2_qd_lru, &qd->qd_lru);
> +               return qd;
>         }
>
>         return NULL;
> @@ -1458,16 +1472,15 @@ int gfs2_quota_init(struct gfs2_sbd *sdp)
>
>                         spin_lock(&qd_lock);
>                         spin_lock_bucket(hash);
> -                       old_qd = gfs2_qd_search_bucket(hash, sdp, qc_id);
> +                       old_qd = gfs2_qd_search_bucket_noref(hash, sdp, qc_id);
> +                       spin_unlock_bucket(hash);
>                         if (old_qd) {
>                                 fs_err(sdp, "Corruption found in quota_change%u"
>                                             "file: duplicate identifier in "
>                                             "slot %u\n",
>                                             sdp->sd_jdesc->jd_jid, slot);
>
> -                               spin_unlock_bucket(hash);

Why didn't you just leave this spin_unlock_bucket() call inside the if
statement?

>                                 spin_unlock(&qd_lock);
> -                               qd_put(old_qd);
>
>                                 gfs2_glock_put(qd->qd_gl);
>                                 kmem_cache_free(gfs2_quotad_cachep, qd);
> @@ -1483,6 +1496,7 @@ int gfs2_quota_init(struct gfs2_sbd *sdp)
>                         BUG_ON(test_and_set_bit(slot, sdp->sd_quota_bitmap));
>                         list_add(&qd->qd_list, &sdp->sd_quota_list);
>                         atomic_inc(&sdp->sd_quota_count);
> +                       spin_lock_bucket(hash);
>                         hlist_bl_add_head_rcu(&qd->qd_hlist, &qd_hash_table[hash]);
>                         spin_unlock_bucket(hash);
>                         spin_unlock(&qd_lock);
> --
> 2.34.1
>

Thanks,
Andreas