Fix scrub resume from newly created hole.

It may happen that scan bookmark points to a block that was turned
into a part of a big hole.  In such case dsl_scan_visitbp() may skip
it and dsl_scan_check_resume() will not be called for it.  As result
new scan suspend won't be possible until the end of the object, that
may take hours if the object is a multi-terabyte ZVOL on a slow HDD
pool, stretching TXG to all that time, creating all sorts of problems.

This patch changes the resume condition to any greater or equal block,
so even if we miss the bookmarked block, the next one we find will
delete the bookmark, allowing new suspend.

Signed-off-by: Alexander Motin <mav@FreeBSD.org>
Sponsored-By: iXsystems, Inc.

include/sys/zio.h

@@ -699,6 +699,8 @@ extern void spa_handle_ignored_writes(spa_t *spa);
 /* zbookmark_phys functions */
 boolean_t zbookmark_subtree_completed(const struct dnode_phys *dnp,
     const zbookmark_phys_t *subtree_root, const zbookmark_phys_t *last_block);
+boolean_t zbookmark_subtree_tbd(const struct dnode_phys *dnp,
+    const zbookmark_phys_t *subtree_root, const zbookmark_phys_t *last_block);
 int zbookmark_compare(uint16_t dbss1, uint8_t ibs1, uint16_t dbss2,
     uint8_t ibs2, const zbookmark_phys_t *zb1, const zbookmark_phys_t *zb2);
 

module/zfs/dsl_scan.c

@@ -1795,12 +1795,11 @@ dsl_scan_check_resume(dsl_scan_t *scn, const dnode_phys_t *dnp,
 
 		/*
 		 * If we found the block we're trying to resume from, or
-		 * we went past it to a different object, zero it out to
-		 * indicate that it's OK to start checking for suspending
-		 * again.
+		 * we went past it, zero it out to indicate that it's OK
+		 * to start checking for suspending again.
 		 */
-		if (bcmp(zb, &scn->scn_phys.scn_bookmark, sizeof (*zb)) == 0 ||
-		    zb->zb_object > scn->scn_phys.scn_bookmark.zb_object) {
+		if (zbookmark_subtree_tbd(dnp, zb,
+		    &scn->scn_phys.scn_bookmark)) {
 			dprintf("resuming at %llx/%llx/%llx/%llx\n",
 			    (longlong_t)zb->zb_objset,
 			    (longlong_t)zb->zb_object,

module/zfs/zio.c

@@ -5008,7 +5008,7 @@ zbookmark_subtree_completed(const dnode_phys_t *dnp,
 {
 	zbookmark_phys_t mod_zb = *subtree_root;
 	mod_zb.zb_blkid++;
-	ASSERT(last_block->zb_level == 0);
+	ASSERT0(last_block->zb_level);
 
 	/* The objset_phys_t isn't before anything. */
 	if (dnp == NULL)
@@ -5034,6 +5034,22 @@ zbookmark_subtree_completed(const dnode_phys_t *dnp,
 	    last_block) <= 0);
 }
 
+/*
+ * This function is similar to zbookmark_subtree_completed(), but returns true
+ * if subtree_root is equal or ahead of last_block, i.e. still to be done.
+ */
+boolean_t
+zbookmark_subtree_tbd(const dnode_phys_t *dnp,
+    const zbookmark_phys_t *subtree_root, const zbookmark_phys_t *last_block)
+{
+	ASSERT0(last_block->zb_level);
+	if (dnp == NULL)
+		return (B_FALSE);
+	return (zbookmark_compare(dnp->dn_datablkszsec, dnp->dn_indblkshift,
+	    1ULL << (DNODE_BLOCK_SHIFT - SPA_MINBLOCKSHIFT), 0, subtree_root,
+	    last_block) >= 0);
+}
+
 EXPORT_SYMBOL(zio_type_name);
 EXPORT_SYMBOL(zio_buf_alloc);
 EXPORT_SYMBOL(zio_data_buf_alloc);