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

Andreas Gruenbacher
2026-04-22T12:10:39Z

Hello,

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

On Tue, Apr 21, 2026 at 10:44 AM Jie Wang <jie.wang@intel.com> 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: syzbot+642d0561f78362d67d3f@syzkaller.appspotmail.com
> Closes: https://syzkaller.appspot.com/bug?extid=642d0561f78362d67d3f
> Tested-by: syzbot+642d0561f78362d67d3f@syzkaller.appspotmail.com
> Signed-off-by: Jie Wang <jie.wang@intel.com>
> ---
> 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