9072 handle error of zap_cursor_retrieve() for log spacemap zap

In spa_ld_log_sm_metadata(), it is possible for zap_cursor_retrieve()
to return errors other than the expected ENOENT (e.g. when we are at
the end of the zap). Ensure that these error cases are handled
correctly by the import path.

Reviewed by: Brian Behlendorf <[email protected]>
Reviewed by: Sara Hartse <[email protected]>
Reviewed by: Matt Ahrens <[email protected]>
Signed-off-by: Serapheim Dimitropoulos <[email protected]>
Closes #9074

1 files changed, 28 insertions, 2 deletions

diff --git a/module/zfs/spa_log_spacemap.c b/module/zfs/spa_log_spacemap.c
index 5733b6c13..bb6610fe0 100644
--- a/module/zfs/spa_log_spacemap.c
+++ b/module/zfs/spa_log_spacemap.c
@@ -989,7 +989,7 @@ spa_ld_log_sm_metadata(spa_t *spa)
 		/* the space map ZAP doesn't exist yet */
 		return (0);
 	} else if (error != 0) {
-		spa_load_failed(spa, "spa_ld_unflushed_txgs(): failed at "
+		spa_load_failed(spa, "spa_ld_log_sm_metadata(): failed at "
 		    "zap_lookup(DMU_POOL_DIRECTORY_OBJECT) [error %d]",
 		    error);
 		return (error);
@@ -998,19 +998,45 @@ spa_ld_log_sm_metadata(spa_t *spa)
 	zap_cursor_t zc;
 	zap_attribute_t za;
 	for (zap_cursor_init(&zc, spa_meta_objset(spa), spacemap_zap);
-	    zap_cursor_retrieve(&zc, &za) == 0; zap_cursor_advance(&zc)) {
+	    (error = zap_cursor_retrieve(&zc, &za)) == 0;
+	    zap_cursor_advance(&zc)) {
 		uint64_t log_txg = zfs_strtonum(za.za_name, NULL);
 		spa_log_sm_t *sls =
 		    spa_log_sm_alloc(za.za_first_integer, log_txg);
 		avl_add(&spa->spa_sm_logs_by_txg, sls);
 	}
 	zap_cursor_fini(&zc);
+	if (error != ENOENT) {
+		spa_load_failed(spa, "spa_ld_log_sm_metadata(): failed at "
+		    "zap_cursor_retrieve(spacemap_zap) [error %d]",
+		    error);
+		return (error);
+	}
 
 	for (metaslab_t *m = avl_first(&spa->spa_metaslabs_by_flushed);
 	    m; m = AVL_NEXT(&spa->spa_metaslabs_by_flushed, m)) {
 		spa_log_sm_t target = { .sls_txg = metaslab_unflushed_txg(m) };
 		spa_log_sm_t *sls = avl_find(&spa->spa_sm_logs_by_txg,
 		    &target, NULL);
+
+		/*
+		 * At this point if sls is zero it means that a bug occurred
+		 * in ZFS the last time the pool was open or earlier in the
+		 * import code path. In general, we would have placed a
+		 * VERIFY() here or in this case just let the kernel panic
+		 * with NULL pointer dereference when incrementing sls_mscount,
+		 * but since this is the import code path we can be a bit more
+		 * lenient. Thus, for DEBUG bits we always cause a panic, while
+		 * in production we log the error and just fail the import.
+		 */
+		ASSERT(sls != NULL);
+		if (sls == NULL) {
+			spa_load_failed(spa, "spa_ld_log_sm_metadata(): bug "
+			    "encountered: could not find log spacemap for "
+			    "TXG %ld [error %d]",
+			    metaslab_unflushed_txg(m), ENOENT);
+			return (ENOENT);
+		}
 		sls->sls_mscount++;
 	}