[AEP]softlockup running dax.sh against latest ext4 dev tree

[quanxian]

Description
Investigate the lockup report running dax.sh against ext4.

[ 17.232155] pmem2: detected capacity change from 0 to 134232408064
[ 238.399253] EXT4-fs (pmem0): DAX enabled. Warning: EXPERIMENTAL, use at your own risk
[ 238.404495] EXT4-fs (pmem0): mounted filesystem with ordered data mode. Opts: dax
[ 238.460013] Injecting memory failure for pfn 0x208900 at process virtual address 0x7f38f1900000
[ 238.462987] Memory failure: 0x208900: Killing dax-pmd:12226 due to hardware memory corruption
[ 238.465781] Memory failure: 0x208900: recovery action for dax page: Recovered
[ 264.699441] watchdog: BUG: soft lockup - CPU#6 stuck for 22s! [dax-pmd:12226]
[..]
[ 264.714244] hardirqs last enabled at (106241291): [<ffffffff81aa09c9>] _raw_spin_unlock_irq+0x29/0x40
[ 264.717185] hardirqs last disabled at (106241292): [<ffffffff810037a3>] trace_hardirqs_off_thunk+0x1a/0x1c
[ 264.720163] softirqs last enabled at (106237250): [<ffffffff81e0032e>] __do_softirq+0x32e/0x428
[ 264.722974] softirqs last disabled at (106237243): [<ffffffff810bc6d6>] irq_exit+0xf6/0x100
[ 264.725701] CPU: 6 PID: 12226 Comm: dax-pmd Tainted: G OE 4.19.0-rc3+ #2350
[ 264.728398] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.11.1-0-g0551a4be2c-prebuilt.qemu-project.org 04/01/2014
[ 264.731851] RIP: 0010:lock_is_held_type+0x46/0x60
[..]
[ 264.757670] Call Trace:
[ 264.758745] find_get_entries+0x195/0x3c0
[ 264.760133] pagevec_lookup_entries+0x1a/0x30
[ 264.761597] dax_layout_busy_page+0x9c/0x280
[ 264.763038] ? __lock_acquire+0x12fa/0x1310
[ 264.764469] ext4_break_layouts+0x48/0x100
[ 264.765869] ? ext4_punch_hole+0x108/0x5a0
[ 264.767267] ext4_punch_hole+0x110/0x5a0
[ 264.768646] ext4_fallocate+0x189/0xa40
[ 264.769999] ? rcu_read_lock_sched_held+0x6b/0x80
[ 264.771532] ? rcu_sync_lockdep_assert+0x2e/0x60
[ 264.773040] vfs_fallocate+0x13f/0x270
[ 264.774373] ksys_fallocate+0x3c/0x70
[ 264.775694] __x64_sys_fallocate+0x1a/0x20
[ 264.777094] do_syscall_64+0x60/0x210
[ 264.778417] entry_SYSCALL_64_after_hwframe+0x49/0xbe

Commits:
d7782145e1ad f52afc93cd01

Target Kernel: 4.19
Target Release: 19.04