Add Linux kmemleak support to ZTS

- Kmemleak `clear` is invoked right before every test case run.
- Kmemleak `scan` is requested right after each test case is finished.
- Kmemleak instrumentation is not used for
  setup/cleanup/pretest/posttest/failsafe stages to shorten the test
  case execution time.
- Kmemleak periodic scan is disabled (`scan=0`) before the test suite
  run to avoid interfering with the on-demand scan results.
- There are unavoidable potential false positives coming from kernel
  areas other than OpenZFS module.
- The ZTS with kmemleak enabled duration is increased by ~50%.

Example run
```
Running Time:   07:12:13
Percent passed: 98.3%

unreferenced object 0xffff9da82aea5410 (size 80):
  comm "kworker/u32:10", pid 942206, jiffies 4296749716 (age 2615.516s)
  hex dump (first 32 bytes):
    00 30 30 00 00 00 00 00 ff 8f 30 00 00 00 00 00  .00.......0.....
    51 e6 77 05 a8 9d ff ff 00 00 00 00 00 00 00 00  Q.w.............
  backtrace:
    [<000000005cf1fea2>] alloc_extent_state+0x1d/0xb0 [btrfs]
    [<0000000083f78ae5>] set_extent_bit+0x2ff/0x670 [btrfs]
    [<00000000de29249e>] lock_extent_bits+0x6b/0xa0 [btrfs]
    [<00000000b241f424>] lock_and_cleanup_extent_if_need+0xaf/0x1c0
       [btrfs]
    [<0000000093ca72b5>] btrfs_buffered_write+0x297/0x7d0 [btrfs]
    [<000000002c2938c8>] btrfs_file_write_iter+0x127/0x390 [btrfs]
    [<00000000b888f720>] do_iter_readv_writev+0x152/0x1b0
    [<00000000320f0bcc>] do_iter_write+0x7c/0x1c0
    [<000000000b5a8fe0>] lo_write_bvec+0x62/0x150 [loop]
    [<000000009aa03c73>] loop_process_work+0x250/0xbd0 [loop]
    [<00000000c7487d8a>] process_one_work+0x1f1/0x390
    [<000000000b236831>] worker_thread+0x53/0x3e0
    [<0000000023cb3e57>] kthread+0x127/0x150
    [<000000002d48676a>] ret_from_fork+0x22/0x30
```

Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Reviewed-by: Ryan Moeller <ryan@iXsystems.com>
Signed-off-by: szubersk <szuberskidamian@gmail.com>
Closes #13084

scripts/zfs-tests.sh

@@ -54,6 +54,7 @@ ZFS_DBGMSG="$STF_SUITE/callbacks/zfs_dbgmsg.ksh"
 ZFS_DMESG="$STF_SUITE/callbacks/zfs_dmesg.ksh"
 UNAME=$(uname -s)
 RERUN=""
+KMEMLEAK=""
 
 # Override some defaults if on FreeBSD
 if [ "$UNAME" = "FreeBSD" ] ; then
@@ -329,6 +330,7 @@ OPTIONS:
 	-S          Enable stack tracer (negative performance impact)
 	-c          Only create and populate constrained path
 	-R          Automatically rerun failing tests
+	-m          Enable kmemleak reporting (Linux only)
 	-n NFSFILE  Use the nfsfile to determine the NFS configuration
 	-I NUM      Number of iterations
 	-d DIR      Use DIR for files and loopback devices
@@ -355,7 +357,7 @@ $0 -x
 EOF
 }
 
-while getopts 'hvqxkfScRn:d:s:r:?t:T:u:I:' OPTION; do
+while getopts 'hvqxkfScRmn:d:s:r:?t:T:u:I:' OPTION; do
 	case $OPTION in
 	h)
 		usage
@@ -386,6 +388,9 @@ while getopts 'hvqxkfScRn:d:s:r:?t:T:u:I:' OPTION; do
 	R)
 		RERUN="yes"
 		;;
+	m)
+		KMEMLEAK="yes"
+		;;
 	n)
 		nfsfile=$OPTARG
 		[ -f "$nfsfile" ] || fail "Cannot read file: $nfsfile"
@@ -695,12 +700,16 @@ fi
 #
 # Run all the tests as specified.
 #
-msg "${TEST_RUNNER} ${QUIET:+-q}" \
+msg "${TEST_RUNNER}" \
+    "${QUIET:+-q}" \
+    "${KMEMLEAK:+-m}" \
     "-c \"${RUNFILES}\"" \
     "-T \"${TAGS}\"" \
     "-i \"${STF_SUITE}\"" \
     "-I \"${ITERATIONS}\""
-{ ${TEST_RUNNER} ${QUIET:+-q} \
+{ ${TEST_RUNNER} \
+    ${QUIET:+-q} \
+    ${KMEMLEAK:+-m} \
     -c "${RUNFILES}" \
     -T "${TAGS}" \
     -i "${STF_SUITE}" \
@@ -722,7 +731,9 @@ if [ "$RESULT" -eq "2" ] && [ -n "$RERUN" ]; then
 	for test_name in $MAYBES; do
 		grep "$test_name " "$TEMP_RESULTS_FILE" >>"$TEST_LIST"
 	done
-	{ ${TEST_RUNNER} ${QUIET:+-q} \
+	{ ${TEST_RUNNER} \
+            ${QUIET:+-q} \
+            ${KMEMLEAK:+-m} \
 	    -c "${RUNFILES}" \
 	    -T "${TAGS}" \
 	    -i "${STF_SUITE}" \