receive_freeobjects() skips freeing some objects

When receiving a FREEOBJECTS record, receive_freeobjects()
incorrectly skips a freed object in some cases. Specifically, this
happens when the first object in the range to be freed doesn't exist,
but the second object does. This leaves an object allocated on disk
on the receiving side which is unallocated on the sending side, which
may cause receiving subsequent incremental streams to fail.

The bug was caused by an incorrect increment of the object index
variable when current object being freed doesn't exist.  The
increment is incorrect because incrementing the object index is
handled by a call to dmu_object_next() in the increment portion of
the for loop statement.

Add test case that exposes this bug.

Reviewed-by: George Melikov <mail@gmelikov.ru>
Reviewed-by: Giuseppe Di Natale <dinatale2@llnl.gov>
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Ned Bass <bass6@llnl.gov>
Closes #6694 
Closes #6695

module/zfs/dmu_send.c

@@ -2563,12 +2563,10 @@ receive_freeobjects(struct receive_writer_arg *rwa,
 		int err;
 
 		err = dmu_object_info(rwa->os, obj, &doi);
-		if (err == ENOENT) {
-			obj++;
+		if (err == ENOENT)
 			continue;
-		} else if (err != 0) {
+		else if (err != 0)
 			return (err);
-		}
 
 		err = dmu_free_long_object(rwa->os, obj);
 		if (err != 0)

tests/runfiles/linux.run

@@ -525,7 +525,7 @@ tests = ['rsend_001_pos', 'rsend_002_pos', 'rsend_003_pos', 'rsend_004_pos',
     'send-c_lz4_disabled', 'send-c_recv_lz4_disabled',
     'send-c_mixed_compression', 'send-c_stream_size_estimate', 'send-cD',
     'send-c_embedded_blocks', 'send-c_resume', 'send-cpL_varied_recsize',
-    'send-c_recv_dedup', 'send_encrypted_heirarchy']
+    'send-c_recv_dedup', 'send_encrypted_heirarchy', 'send_freeobjects']
 
 [tests/functional/scrub_mirror]
 tests = ['scrub_mirror_001_pos', 'scrub_mirror_002_pos',

tests/zfs-tests/tests/functional/rsend/Makefile.am

@@ -38,4 +38,5 @@ dist_pkgdata_SCRIPTS = \
 	send-c_verify_ratio.ksh \
 	send-c_volume.ksh \
 	send-c_zstreamdump.ksh \
-	send-cpL_varied_recsize.ksh
+	send-cpL_varied_recsize.ksh \
+	send_freeobjects.ksh

tests/zfs-tests/tests/functional/rsend/send_freeobjects.ksh

@@ -0,0 +1,81 @@
+#!/bin/ksh
+
+#
+# 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) 2017 by Lawrence Livermore National Security, LLC.
+#
+
+. $STF_SUITE/include/libtest.shlib
+. $STF_SUITE/tests/functional/rsend/rsend.kshlib
+
+#
+# Description:
+# Verify FREEOBJECTS record frees sequential objects (See
+# https://github.com/zfsonlinux/zfs/issues/6694)
+#
+# Strategy:
+# 1. Create three files with sequential object numbers, f1 f2 and f3
+# 2. Delete f2
+# 3. Take snapshot A
+# 4. Delete f3
+# 5. Take snapshot B
+# 6. Receive a full send of A
+# 7. Receive an incremental send of B
+# 8. Fail test if f3 exists on received snapshot B
+#
+
+verify_runnable "both"
+
+log_assert "Verify FREEOBJECTS record frees sequential objects"
+
+sendds=sendfo
+recvds=recvfo
+f1=/$POOL/$sendds/f1
+f2=/$POOL/$sendds/f2
+f3=/$POOL/$sendds/f3
+
+#
+# We need to set xattr=sa and dnodesize=legacy to guarantee sequential
+# object numbers for this test. Otherwise, if we used directory-based
+# xattrs, SELinux extended attributes might consume intervening object
+# numbers.
+#
+log_must zfs create -o xattr=sa -o dnodesize=legacy $POOL/$sendds
+
+tries=100
+for ((i=0; i<$tries; i++)); do
+	touch $f1 $f2 $f3
+	o1=$(ls -li $f1 | awk '{print $1}')
+	o2=$(ls -li $f2 | awk '{print $1}')
+	o3=$(ls -li $f3 | awk '{print $1}')
+
+	if [[ $o2 -ne $(( $o1 + 1 )) ]] || [[ $o3 -ne $(( $o2 + 1 )) ]]; then
+		rm -f $f1 $f2 $f3
+	else
+		break
+	fi
+done
+
+if [[ $i -eq $tries ]]; then
+	log_fail "Failed to create three sequential objects"
+fi
+
+log_must rm $f2
+log_must zfs snap $POOL/$sendds@A
+log_must rm $f3
+log_must zfs snap $POOL/$sendds@B
+log_must eval "zfs send $POOL/$sendds@A | zfs recv $POOL/$recvds"
+log_must eval "zfs send -i $POOL/$sendds@A $POOL/$sendds@B |" \
+	"zfs recv $POOL/$recvds"
+log_mustnot zdb $POOL/$recvds@B $o3
+log_pass "Verify FREEOBJECTS record frees sequential objects"