Re: [PATCH] gfs2: fix quota init duplicate scan

Andreas Gruenbacher
2026-04-20T12:36:11Z

Hello,

thank you for the patch.

On Mon, Apr 20, 2026 at 5:20 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.

That should work ... but with that, can you at least implement
gfs2_qd_search_bucket() on top of gfs2_qd_search_bucket_noref()? Or
better yet, convert qd_hash_table into an rhashtable, like
gl_hash_table already is? That should allow a normal ref taking lookup
even on PREEMPT_RT.

> Also save the current qc pointer before iterator advance, and clear that
> saved slot on duplicate so the correct on-disk entry is zeroed.

This needs to go into a separate patch. Also, why not put the 'qc++'
into the third expression of the surrounding for loop?

> 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 | 28 ++++++++++++++++++++++++----
> 1 file changed, 24 insertions(+), 4 deletions(-)
>
> diff --git a/fs/gfs2/quota.c b/fs/gfs2/quota.c
> index 5290865f27f1..0191ba211670 100644
> --- a/fs/gfs2/quota.c
> +++ b/fs/gfs2/quota.c
> @@ -275,6 +275,25 @@ static struct gfs2_quota_data *gfs2_qd_search_bucket(unsigned int hash,
> return NULL;
> }
>
> +/*
> + * 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;
> +
> + 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)
> + return qd;
> + }
> +
> + return NULL;
> +}
> +
>
> static int qd_get(struct gfs2_sbd *sdp, struct kqid qid,
> struct gfs2_quota_data **qdp)
> @@ -1435,6 +1454,7 @@ int gfs2_quota_init(struct gfs2_sbd *sdp)
> for (y = 0; y < sdp->sd_qc_per_block && slot < sdp->sd_quota_slots;
> y++, slot++) {
> struct gfs2_quota_data *old_qd, *qd;
> + struct gfs2_quota_change *dup_qc = qc;
> s64 qc_change = be64_to_cpu(qc->qc_change);
> u32 qc_flags = be32_to_cpu(qc->qc_flags);
> enum quota_type qtype = (qc_flags & GFS2_QCF_USER) ?
> @@ -1458,23 +1478,22 @@ 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);
> spin_unlock(&qd_lock);
> - qd_put(old_qd);
>
> gfs2_glock_put(qd->qd_gl);
> kmem_cache_free(gfs2_quotad_cachep, qd);
>
> /* zero out the duplicate slot */
> lock_buffer(bh);
> - memset(qc, 0, sizeof(*qc));
> + memset(dup_qc, 0, sizeof(*dup_qc));
> mark_buffer_dirty(bh);
> unlock_buffer(bh);
>
> @@ -1483,6 +1502,7 @@ 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