FYI, we noticed the following commit (built with gcc-7):

commit: f5c9b46c08fe18a5cd66c52e8e07c49476376d74 ("btrfs: Convert to using fs_context")
https://git.kernel.org/cgit/linux/kernel/git/viro/vfs.git Q27

in testcase: xfstests
with following parameters:

	disk: 6HDD
	fs: btrfs
	test: btrfs-group1

test-description: xfstests is a regression test suite for xfs and other files ystems.
test-url: git://git.kernel.org/pub/scm/fs/xfs/xfstests-dev.git


on test machine: qemu-system-x86_64 -enable-kvm -cpu SandyBridge -smp 2 -m 4G

caused below changes (please refer to attached dmesg/kmsg for entire log/backtrace):


+------------------------------------------------+------------+------------+
|                                                | c49b0d9aad | f5c9b46c08 |
+------------------------------------------------+------------+------------+
| boot_successes                                 | 5          | 10         |
| boot_failures                                  | 4          | 12         |
| End_of_test:RCU_HOTPLUG                        | 4          |            |
| BUG:soft_lockup-CPU##stuck_for#s               | 0          | 12         |
| RIP:native_queued_spin_lock_slowpath           | 0          | 12         |
| Kernel_panic-not_syncing:softlockup:hung_tasks | 0          | 12         |
+------------------------------------------------+------------+------------+



[  176.538777] watchdog: BUG: soft lockup - CPU#1 stuck for 22s! [kworker/u4:2:152]
[  176.542675] Modules linked in: btrfs xor zstd_decompress zstd_compress xxhash raid6_pq dm_mod sr_mod cdrom sg ata_generic pata_acpi crct10dif_pclmul crc32_pclmul crc32c_intel ghash_clmulni_intel ppdev aesni_intel crypto_simd cryptd glue_helper snd_pcm snd_timer snd soundcore serio_raw pcspkr ata_piix i2c_piix4 libata parport_pc floppy parport ip_tables
[  176.547111] CPU: 1 PID: 152 Comm: kworker/u4:2 Not tainted 4.20.0-rc1-00072-gf5c9b46 #1
[  176.548379] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.10.2-1 04/01/2014
[  176.549719] Workqueue: btrfs-delalloc btrfs_delalloc_helper [btrfs]
[  176.550666] RIP: 0010:native_queued_spin_lock_slowpath+0x21/0x1a0
[  176.551581] Code: 2e 0f 1f 84 00 00 00 00 00 66 66 66 66 90 66 66 66 66 90 ba 01 00 00 00 8b 07 85 c0 75 0a f0 0f b1 17 85 c0 75 f2 f3 c3 f3 90 <eb> ec 81 fe 00 01 00 00 74 3e 81 e6 00 ff ff ff 75 56 f0 0f ba 2f
[  176.554262] RSP: 0000:ffffc900008d7cb0 EFLAGS: 00000202 ORIG_RAX: ffffffffffffff13
[  176.555479] RAX: 0000000000000001 RBX: ffffffffffffffff RCX: ffffffffa0433fc8
[  176.556523] RDX: 0000000000000001 RSI: 0000000000000001 RDI: ffffffffa0433fb8
[  176.557568] RBP: ffffffffa0433fb8 R08: 0000000000000002 R09: ffffc900008d7df0
[  176.558615] R10: ffffffff82844be0 R11: 0000000000000002 R12: ffffffffa0433fc0
[  176.559666] R13: ffffffffa0433fa8 R14: 0000000000000002 R15: 0000000000000000
[  176.560708] FS:  0000000000000000(0000) GS:ffff88013fd00000(0000) knlGS:0000000000000000
[  176.561983] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[  176.562860] CR2: 000055b2ad0f72f0 CR3: 000000007852c000 CR4: 00000000000406e0
[  176.563907] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
[  176.564952] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
[  176.565997] Call Trace:
[  176.566489]  _raw_spin_lock+0x22/0x30
[  176.567136]  __find_workspace+0x9d/0x2c0 [btrfs]
[  176.567895]  ? btrfs_compress_heuristic+0x1b5/0x560 [btrfs]
[  176.568759]  ? page_mkclean+0x6e/0xc0
[  176.569387]  ? page_referenced_one+0x1a0/0x1a0
[  176.570126]  btrfs_compress_pages+0x38/0xa0 [btrfs]
[  176.570913]  compress_file_range+0x201/0x7b0 [btrfs]
[  176.571843]  ? submit_compressed_extents+0x4e0/0x4e0 [btrfs]
[  176.572720]  async_cow_start+0x43/0x80 [btrfs]
[  176.573453]  normal_work_helper+0x79/0x350 [btrfs]
[  176.574222]  ? __schedule+0x268/0x8a0
[  176.574850]  process_one_work+0x1ae/0x3d0
[  176.575518]  worker_thread+0x3c/0x3b0
[  176.576148]  ? process_one_work+0x3d0/0x3d0
[  176.576842]  kthread+0x11e/0x140
[  176.577417]  ? kthread_park+0x90/0x90
[  176.578046]  ret_from_fork+0x35/0x40
[  176.578667] Kernel panic - not syncing: softlockup: hung tasks
[  176.579551] CPU: 1 PID: 152 Comm: kworker/u4:2 Tainted: G             L    4.20.0-rc1-00072-gf5c9b46 #1
[  176.580989] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.10.2-1 04/01/2014
[  176.582310] Workqueue: btrfs-delalloc btrfs_delalloc_helper [btrfs]
[  176.583240] Call Trace:
[  176.583709]  <IRQ>
[  176.584124]  dump_stack+0x5c/0x7b
[  176.584696]  panic+0xfe/0x262
[  176.585222]  ? ret_from_fork+0x21/0x40
[  176.585841]  ? ret_from_fork+0x1a/0x40
[  176.586457]  watchdog_timer_fn+0x256/0x260
[  176.587143]  ? softlockup_fn+0x40/0x40
[  176.587784]  __hrtimer_run_queues+0x108/0x2b0
[  176.588465]  hrtimer_interrupt+0xe5/0x240
[  176.589112]  smp_apic_timer_interrupt+0x6a/0x150
[  176.589828]  apic_timer_interrupt+0xf/0x20
[  176.590479]  </IRQ>
[  176.590906] RIP: 0010:native_queued_spin_lock_slowpath+0x21/0x1a0
[  176.591795] Code: 2e 0f 1f 84 00 00 00 00 00 66 66 66 66 90 66 66 66 66 90 ba 01 00 00 00 8b 07 85 c0 75 0a f0 0f b1 17 85 c0 75 f2 f3 c3 f3 90 <eb> ec 81 fe 00 01 00 00 74 3e 81 e6 00 ff ff ff 75 56 f0 0f ba 2f
[  176.594369] RSP: 0000:ffffc900008d7cb0 EFLAGS: 00000202 ORIG_RAX: ffffffffffffff13
[  176.595568] RAX: 0000000000000001 RBX: ffffffffffffffff RCX: ffffffffa0433fc8
[  176.596619] RDX: 0000000000000001 RSI: 0000000000000001 RDI: ffffffffa0433fb8
[  176.597639] RBP: ffffffffa0433fb8 R08: 0000000000000002 R09: ffffc900008d7df0
[  176.598657] R10: ffffffff82844be0 R11: 0000000000000002 R12: ffffffffa0433fc0
[  176.599670] R13: ffffffffa0433fa8 R14: 0000000000000002 R15: 0000000000000000
[  176.600695]  _raw_spin_lock+0x22/0x30
[  176.601317]  __find_workspace+0x9d/0x2c0 [btrfs]
[  176.602052]  ? btrfs_compress_heuristic+0x1b5/0x560 [btrfs]
[  176.602891]  ? page_mkclean+0x6e/0xc0
[  176.603497]  ? page_referenced_one+0x1a0/0x1a0
[  176.604206]  btrfs_compress_pages+0x38/0xa0 [btrfs]
[  176.604967]  compress_file_range+0x201/0x7b0 [btrfs]
[  176.605866]  ? submit_compressed_extents+0x4e0/0x4e0 [btrfs]
[  176.606716]  async_cow_start+0x43/0x80 [btrfs]
[  176.607423]  normal_work_helper+0x79/0x350 [btrfs]
[  176.608166]  ? __schedule+0x268/0x8a0
[  176.608775]  process_one_work+0x1ae/0x3d0
[  176.609420]  worker_thread+0x3c/0x3b0
[  176.610032]  ? process_one_work+0x3d0/0x3d0
[  176.610701]  kthread+0x11e/0x140
[  176.611256]  ? kthread_park+0x90/0x90
[  176.611864]  ret_from_fork+0x35/0x40
[  176.612485] Kernel Offset: disabled

Elapsed time: 180

#!/bin/bash

# To reproduce,
# 1) save job-script and this script (both are attached in 0day report email)
# 2) run this script with your compiled kernel and optional env $INSTALL_MOD_PATH

kernel=$1

initrds=(
	/osimage/debian/debian-x86_64-2018-04-03.cgz
	/lkp/lkp/lkp-x86_64.cgz
	/osimage/deps/debian-x86_64-2018-04-03.cgz/run-ipconfig_2018-04-03.cgz
	/osimage/deps/debian-x86_64-2018-04-03.cgz/lkp_2018-04-03.cgz
	/osimage/deps/debian-x86_64-2018-04-03.cgz/rsync-rootfs_2018-04-03.cgz
	/osimage/deps/debian-x86_64-2018-04-03.cgz/fs_2018-06-12.cgz
	/osimage/deps/debian-x86_64-2018-04-03.cgz/xfstests_2018-08-30.cgz
	/osimage/pkg/debian-x86_64-2018-04-03.cgz/xfstests-x86_64-cc8831f9_2018-09-19.cgz
)



To reproduce:

        git clone https://github.com/intel/lkp-tests.git
        cd lkp-tests
        bin/lkp qemu -k <bzImage> job-script # job-script is attached in this email



Thanks,
Rong Chen