[PATCH] gfs2: fix quota init duplicate scan

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.

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 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 | 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