Livelist logic should handle dedup blkptrs

Update the logic to handle the dedup-case of consecutive
FREEs in the livelist code. The logic still ensures that
all the FREE entries are matched up with a respective
ALLOC by keeping a refcount for each FREE blkptr that we
encounter and ensuring that this refcount gets to zero
by the time we are done processing the livelist.

zdb -y no longer panics when encountering double frees

Reviewed-by: Matthew Ahrens <mahrens@delphix.com>
Reviewed-by: John Kennedy <john.kennedy@delphix.com>
Reviewed-by: Don Brady <don.brady@delphix.com>
Signed-off-by: Serapheim Dimitropoulos <serapheim@delphix.com>
Closes #11480
Closes #12177

tests/runfiles/common.run

@@ -166,8 +166,8 @@ tags = ['functional', 'cli_root', 'zfs_create']
 
 [tests/functional/cli_root/zfs_destroy]
 tests = ['zfs_clone_livelist_condense_and_disable',
-    'zfs_clone_livelist_condense_races', 'zfs_destroy_001_pos',
-    'zfs_destroy_002_pos', 'zfs_destroy_003_pos',
+    'zfs_clone_livelist_condense_races', 'zfs_clone_livelist_dedup',
+    'zfs_destroy_001_pos', 'zfs_destroy_002_pos', 'zfs_destroy_003_pos',
     'zfs_destroy_004_pos', 'zfs_destroy_005_neg', 'zfs_destroy_006_neg',
     'zfs_destroy_007_neg', 'zfs_destroy_008_pos', 'zfs_destroy_009_pos',
     'zfs_destroy_010_pos', 'zfs_destroy_011_pos', 'zfs_destroy_012_pos',

tests/zfs-tests/tests/functional/cli_root/zfs_destroy/zfs_clone_livelist_dedup.ksh

@@ -0,0 +1,88 @@
+#!/bin/ksh -p
+#
+# This file and its contents are supplied under the terms of the
+# Common Development and Distribution License ("CDDL"), version 1.0.
+# You may only use this file in accordance with the terms of version
+# 1.0 of the CDDL.
+#
+# A full copy of the text of the CDDL should have accompanied this
+# source.  A copy of the CDDL is also available via the Internet at
+# http://www.illumos.org/license/CDDL.
+#
+
+#
+# Copyright (c) 2021 by Delphix. All rights reserved.
+#
+
+# DESCRIPTION
+# Verify zfs destroy test for clones with livelists that contain
+# dedup blocks. This test is a baseline regression test created
+# to ensure that past bugs that we've encountered between dedup
+# and the livelist logic don't resurface.
+
+# STRATEGY
+# 1. Create a clone from a test filesystem and enable dedup.
+# 2. Write some data and create a livelist.
+# 3. Copy the data within the clone to create dedup blocks.
+# 4. Remove some of the dedup data to create multiple free
+#    entries for the same block pointers.
+# 5. Process all the livelist entries by destroying the clone.
+
+. $STF_SUITE/include/libtest.shlib
+. $STF_SUITE/tests/functional/cli_root/zfs_destroy/zfs_destroy_common.kshlib
+
+function cleanup
+{
+	log_must zfs destroy -Rf $TESTPOOL/$TESTFS1
+	# Reset the minimum percent shared to 75
+	set_tunable32 LIVELIST_MIN_PERCENT_SHARED $ORIGINAL_MIN_SHARED
+}
+
+function test_dedup
+{
+	# Set a small percent shared threshold so the livelist is not disabled
+	set_tunable32 LIVELIST_MIN_PERCENT_SHARED 10
+	clone_dataset $TESTFS1 snap $TESTCLONE
+
+	# Enable dedup
+	log_must zfs set dedup=on $TESTPOOL/$TESTCLONE
+
+	# Create some data to be deduped
+	log_must dd if=/dev/urandom of="/$TESTPOOL/$TESTCLONE/data" bs=512 count=10k
+
+	# Create dedup blocks
+	# Note: We sync before and after so all dedup blocks belong to the
+	#       same TXG, otherwise they won't look identical to the livelist
+	#       iterator due to their logical birth TXG being different.
+	log_must zpool sync $TESTPOOL
+	log_must cp /$TESTPOOL/$TESTCLONE/data /$TESTPOOL/$TESTCLONE/data-dup-0
+	log_must cp /$TESTPOOL/$TESTCLONE/data /$TESTPOOL/$TESTCLONE/data-dup-1
+	log_must cp /$TESTPOOL/$TESTCLONE/data /$TESTPOOL/$TESTCLONE/data-dup-2
+	log_must cp /$TESTPOOL/$TESTCLONE/data /$TESTPOOL/$TESTCLONE/data-dup-3
+	log_must zpool sync $TESTPOOL
+	check_livelist_exists $TESTCLONE
+
+	# Introduce "double frees"
+	#   We want to introduce consecutive FREEs of the same block as this
+	#   was what triggered past panics.
+	# Note: Similarly to the previouys step we sync before and after our
+	#       our deletions so all the entries end up in the same TXG.
+	log_must zpool sync $TESTPOOL
+	log_must rm /$TESTPOOL/$TESTCLONE/data-dup-2
+	log_must rm /$TESTPOOL/$TESTCLONE/data-dup-3
+	log_must zpool sync $TESTPOOL
+	check_livelist_exists $TESTCLONE
+
+	log_must zfs destroy $TESTPOOL/$TESTCLONE
+	check_livelist_gone
+}
+
+ORIGINAL_MIN_SHARED=$(get_tunable LIVELIST_MIN_PERCENT_SHARED)
+
+log_onexit cleanup
+log_must zfs create $TESTPOOL/$TESTFS1
+log_must mkfile 5m /$TESTPOOL/$TESTFS1/atestfile
+log_must zfs snapshot $TESTPOOL/$TESTFS1@snap
+test_dedup
+
+log_pass "Clone's livelist processes dedup blocks as expected."