[RFC 2/2] ext4/061: Regression test of jbd2 journal_task race against unmount

["Ritesh Harjani (IBM)" <ritesh.list@gmail.com>]

This test adds a testcase to catch race condition against
reading of journal_task and parallel unmount.
This patch in kernel fixes this [1]

    ext4_put_super()                cat /sys/fs/ext4/loop2/journal_task
            |                               ext4_attr_show();
    ext4_jbd2_journal_destroy();                    |
            |                                journal_task_show()
            |                                       |
            |                               task_pid_vnr(NULL);
    sbi->s_journal = NULL;

RIP: 0010:__task_pid_nr_ns+0x4d/0xe0
<...>
Call Trace:
 <TASK>
 ext4_attr_show+0x1bd/0x3e0
 sysfs_kf_seq_show+0x8e/0x110
 seq_read_iter+0x11b/0x4d0
 vfs_read+0x216/0x2e0
 ksys_read+0x69/0xf0
 do_syscall_64+0x3f/0x90
 entry_SYSCALL_64_after_hwframe+0x72/0xdc
[

[1]: https://lore.kernel.org/all/20200318061301.4320-1-riteshh@linux.ibm.com/
Commit: ext4: Unregister sysfs path before destroying jbd2 journal

Signed-off-by: Ritesh Harjani (IBM) <ritesh.list@gmail.com>
---
 tests/ext4/061     | 82 ++++++++++++++++++++++++++++++++++++++++++++++
 tests/ext4/061.out |  2 ++
 2 files changed, 84 insertions(+)
 create mode 100755 tests/ext4/061
 create mode 100644 tests/ext4/061.out

diff --git a/tests/ext4/061 b/tests/ext4/061
new file mode 100755
index 00000000..88bf138a
--- /dev/null
+++ b/tests/ext4/061
@@ -0,0 +1,82 @@
+#! /bin/bash
+# SPDX-License-Identifier: GPL-2.0
+# Copyright (c) 2023 IBM Corporation.  All Rights Reserved.
+#
+# FS QA Test 061
+#
+# Regression test for https://lore.kernel.org/all/20200318061301.4320-1-riteshh@linux.ibm.com/
+# ext4: Unregister sysfs path before destroying jbd2 journal
+#
+
+. ./common/preamble
+_begin_fstest auto quick
+
+pid_mloop=""
+pids_jloop=""
+trap "_cleanup; exit \$status" 0 1 2 3 15
+# Override the default cleanup function.
+_cleanup()
+{
+	{
+		kill -SIGKILL $pid_mloop $pids_jloop
+		wait $pid_mloop $pids_jloop
+	} > /dev/null 2>&1
+	cd /
+	rm -r -f $tmp.*
+}
+
+# Import common functions.
+. ./common/filter
+
+# real QA test starts here
+
+# Modify as appropriate.
+_supported_fs ext4
+_fixed_by_kernel_commit 5e47868fb94b63c \
+	"ext4: unregister sysfs path before destroying jbd2 journal"
+_require_scratch
+_require_fs_sysfs journal_task
+
+_scratch_mkfs_ext4 >> $seqres.full 2>&1
+# mount filesystem
+_scratch_mount >> $seqres.full 2>&1
+scratch_dev=$(_short_dev $SCRATCH_DEV)
+
+function mount_loop()
+{
+	while [ 1 ]; do
+		_scratch_unmount >> $seqres.full 2>&1
+		sleep 1;
+		_scratch_mount >> $seqres.full 2>&1
+		sleep 1;
+	done
+}
+
+function read_journal_task_loop()
+{
+	while [ 1 ]; do
+		cat /sys/fs/ext4/$scratch_dev/journal_task > /dev/null 2>&1
+		sleep 1;
+	done
+}
+
+mount_loop &
+pid_mloop=$!
+
+for i in $(seq 1 100); do
+	read_journal_task_loop &
+	pid=$!
+	pids_jloop="${pids_jloop} ${pid}"
+done
+
+sleep 20
+{
+	kill -SIGKILL $pid_mloop $pids_jloop
+	wait $pid_mloop $pids_jloop
+} > /dev/null 2>&1
+
+echo "Silence is golden"
+
+# success, all done
+status=0
+exit
diff --git a/tests/ext4/061.out b/tests/ext4/061.out
new file mode 100644
index 00000000..273be9e0
--- /dev/null
+++ b/tests/ext4/061.out
@@ -0,0 +1,2 @@
+QA output created by 061
+Silence is golden
--
2.39.2