Illumos 6267 - dn_bonus evicted too early

6267 dn_bonus evicted too early
Reviewed by: Richard Yao <[email protected]>
Reviewed by: Xin LI <[email protected]>
Reviewed by: Matthew Ahrens <[email protected]>
Approved by: Richard Lowe <[email protected]>

References:
  https://www.illumos.org/issues/6267
  illumos/illumos-gate@d205810

Signed-off-by: Brian Behlendorf <[email protected]>
Ported-by: Ned Bass [email protected]
Issue #3865
Issue #3443

include/sys/dbuf.h

@@ -230,9 +230,25 @@ typedef struct dmu_buf_impl {
 	/* User callback information. */
 	dmu_buf_user_t *db_user;
 
-	uint8_t db_immediate_evict;
+	/*
+	 * Evict user data as soon as the dirty and reference
+	 * counts are equal.
+	 */
+	uint8_t db_user_immediate_evict;
+
+	/*
+	 * This block was freed while a read or write was
+	 * active.
+	 */
 	uint8_t db_freed_in_flight;
 
+	/*
+	 * dnode_evict_dbufs() or dnode_evict_bonus() tried to
+	 * evict this dbuf, but couldn't due to outstanding
+	 * references.  Evict once the refcount drops to 0.
+	 */
+	uint8_t db_pending_evict;
+
 	uint8_t db_dirtycnt;
 } dmu_buf_impl_t;
 

include/sys/dmu_objset.h

@@ -93,7 +93,6 @@ struct objset {
 	uint8_t os_copies;
 	enum zio_checksum os_dedup_checksum;
 	boolean_t os_dedup_verify;
-	boolean_t os_evicting;
 	zfs_logbias_op_t os_logbias;
 	zfs_cache_type_t os_primary_cache;
 	zfs_cache_type_t os_secondary_cache;

module/zfs/dbuf.c

@@ -303,7 +303,7 @@ dbuf_verify_user(dmu_buf_impl_t *db, dbvu_verify_type_t verify_type)
 		 */
 		ASSERT3U(holds, >=, db->db_dirtycnt);
 	} else {
-		if (db->db_immediate_evict == TRUE)
+		if (db->db_user_immediate_evict == TRUE)
 			ASSERT3U(holds, >=, db->db_dirtycnt);
 		else
 			ASSERT3U(holds, >, 0);
@@ -1880,8 +1880,9 @@ dbuf_create(dnode_t *dn, uint8_t level, uint64_t blkid,
 	db->db_blkptr = blkptr;
 
 	db->db_user = NULL;
-	db->db_immediate_evict = 0;
-	db->db_freed_in_flight = 0;
+	db->db_user_immediate_evict = FALSE;
+	db->db_freed_in_flight = FALSE;
+	db->db_pending_evict = FALSE;
 
 	if (blkid == DMU_BONUS_BLKID) {
 		ASSERT3P(parent, ==, dn->dn_dbuf);
@@ -2318,12 +2319,13 @@ dbuf_rele_and_unlock(dmu_buf_impl_t *db, void *tag)
 		arc_buf_freeze(db->db_buf);
 
 	if (holds == db->db_dirtycnt &&
-	    db->db_level == 0 && db->db_immediate_evict)
+	    db->db_level == 0 && db->db_user_immediate_evict)
 		dbuf_evict_user(db);
 
 	if (holds == 0) {
 		if (db->db_blkid == DMU_BONUS_BLKID) {
 			dnode_t *dn;
+			boolean_t evict_dbuf = db->db_pending_evict;
 
 			/*
 			 * If the dnode moves here, we cannot cross this
@@ -2338,7 +2340,7 @@ dbuf_rele_and_unlock(dmu_buf_impl_t *db, void *tag)
 			 * Decrementing the dbuf count means that the bonus
 			 * buffer's dnode hold is no longer discounted in
 			 * dnode_move(). The dnode cannot move until after
-			 * the dnode_rele_and_unlock() below.
+			 * the dnode_rele() below.
 			 */
 			DB_DNODE_EXIT(db);
 
@@ -2348,35 +2350,10 @@ dbuf_rele_and_unlock(dmu_buf_impl_t *db, void *tag)
 			 */
 			mutex_exit(&db->db_mtx);
 
-			/*
-			 * If the dnode has been freed, evict the bonus
-			 * buffer immediately.	The data in the bonus
-			 * buffer is no longer relevant and this prevents
-			 * a stale bonus buffer from being associated
-			 * with this dnode_t should the dnode_t be reused
-			 * prior to being destroyed.
-			 */
-			mutex_enter(&dn->dn_mtx);
-			if (dn->dn_type == DMU_OT_NONE ||
-			    dn->dn_free_txg != 0) {
-				/*
-				 * Drop dn_mtx.  It is a leaf lock and
-				 * cannot be held when dnode_evict_bonus()
-				 * acquires other locks in order to
-				 * perform the eviction.
-				 *
-				 * Freed dnodes cannot be reused until the
-				 * last hold is released.  Since this bonus
-				 * buffer has a hold, the dnode will remain
-				 * in the free state, even without dn_mtx
-				 * held, until the dnode_rele_and_unlock()
-				 * below.
-				 */
-				mutex_exit(&dn->dn_mtx);
+			if (evict_dbuf)
 				dnode_evict_bonus(dn);
-				mutex_enter(&dn->dn_mtx);
-			}
-			dnode_rele_and_unlock(dn, db);
+
+			dnode_rele(dn, db);
 		} else if (db->db_buf == NULL) {
 			/*
 			 * This is a special case: we never associated this
@@ -2423,7 +2400,7 @@ dbuf_rele_and_unlock(dmu_buf_impl_t *db, void *tag)
 				} else {
 					dbuf_clear(db);
 				}
-			} else if (db->db_objset->os_evicting ||
+			} else if (db->db_pending_evict ||
 			    arc_buf_eviction_needed(db->db_buf)) {
 				dbuf_clear(db);
 			} else {
@@ -2471,7 +2448,7 @@ dmu_buf_set_user_ie(dmu_buf_t *db_fake, dmu_buf_user_t *user)
 {
 	dmu_buf_impl_t *db = (dmu_buf_impl_t *)db_fake;
 
-	db->db_immediate_evict = TRUE;
+	db->db_user_immediate_evict = TRUE;
 	return (dmu_buf_set_user(db_fake, user));
 }
 

module/zfs/dmu_objset.c

@@ -726,7 +726,6 @@ dmu_objset_evict(objset_t *os)
 	if (os->os_sa)
 		sa_tear_down(os);
 
-	os->os_evicting = B_TRUE;
 	dmu_objset_evict_dbufs(os);
 
 	mutex_enter(&os->os_lock);

module/zfs/dnode_sync.c

@@ -432,6 +432,7 @@ dnode_evict_dbufs(dnode_t *dn)
 			db_next = AVL_NEXT(&dn->dn_dbufs, db_marker);
 			avl_remove(&dn->dn_dbufs, db_marker);
 		} else {
+			db->db_pending_evict = TRUE;
 			mutex_exit(&db->db_mtx);
 			db_next = AVL_NEXT(&dn->dn_dbufs, db);
 		}
@@ -447,10 +448,14 @@ void
 dnode_evict_bonus(dnode_t *dn)
 {
 	rw_enter(&dn->dn_struct_rwlock, RW_WRITER);
-	if (dn->dn_bonus && refcount_is_zero(&dn->dn_bonus->db_holds)) {
-		mutex_enter(&dn->dn_bonus->db_mtx);
-		dbuf_evict(dn->dn_bonus);
-		dn->dn_bonus = NULL;
+	if (dn->dn_bonus != NULL) {
+		if (refcount_is_zero(&dn->dn_bonus->db_holds)) {
+			mutex_enter(&dn->dn_bonus->db_mtx);
+			dbuf_evict(dn->dn_bonus);
+			dn->dn_bonus = NULL;
+		} else {
+			dn->dn_bonus->db_pending_evict = TRUE;
+		}
 	}
 	rw_exit(&dn->dn_struct_rwlock);
 }
@@ -502,7 +507,6 @@ dnode_sync_free(dnode_t *dn, dmu_tx_t *tx)
 
 	dnode_undirty_dbufs(&dn->dn_dirty_records[txgoff]);
 	dnode_evict_dbufs(dn);
-	ASSERT(avl_is_empty(&dn->dn_dbufs));
 
 	/*
 	 * XXX - It would be nice to assert this, but we may still