WARN_ON_ONCE() during generic/270

[Ross Zwisler <ross.zwisler@xxxxxxxxxxxxxxx>]

I hit the following WARN_ON_ONCE() during generic/270 with xfs (passed through
kasan_symbolize.py):

  run fstests generic/270 at 2017-02-08 10:56:07
  XFS (pmem0p2): Unmounting Filesystem
  XFS (pmem0p2): DAX enabled. Warning: EXPERIMENTAL, use at your own risk
  XFS (pmem0p2): Mounting V5 Filesystem
  XFS (pmem0p2): Ending clean mount
  XFS (pmem0p2): Quotacheck needed: Please wait.
  XFS (pmem0p2): Quotacheck: Done.
  XFS (pmem0p2): xlog_verify_grant_tail: space > BBTOB(tail_blocks)
  ------------[ cut here ]------------
  WARNING: CPU: 7 PID: 23652 at fs/xfs/libxfs/xfs_bmap.c:5981[<      none      
>] xfs_bmse_shift_one+0x3da/0x4c0 fs/xfs/libxfs/xfs_bmap.c:5981
  Modules linked in: dax_pmem nd_pmem dax nd_btt nd_e820 libnvdimm
  CPU: 4 PID: 23652 Comm: 23288.fsstress. Not tainted 
4.10.0-rc7-00065-g926af627 #1
  Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.9.1-1.fc24 
04/01/2014
  Call Trace:
  [<     inline     >] __dump_stack lib/dump_stack.c:15
  [<      none      >] dump_stack+0x86/0xc3 lib/dump_stack.c:51
  [<      none      >] __warn+0xcb/0xf0 kernel/panic.c:547
  [<      none      >] warn_slowpath_null+0x1d/0x20 kernel/panic.c:582
  [<      none      >] xfs_bmse_shift_one+0x3da/0x4c0 
fs/xfs/libxfs/xfs_bmap.c:5981
  [<      none      >] xfs_bmap_shift_extents+0x305/0x490 
fs/xfs/libxfs/xfs_bmap.c:6144
  [<      none      >] xfs_shift_file_space+0x25f/0x320 
fs/xfs/xfs_bmap_util.c:1475
  [<      none      >] xfs_insert_file_space+0x5a/0x180 
fs/xfs/xfs_bmap_util.c:1548
  [<      none      >] xfs_file_fallocate+0x34c/0x3b0 fs/xfs/xfs_file.c:844
   ?[<      none      >] rcu_sync_lockdep_assert+0x2f/0x60 kernel/rcu/sync.c:68
  [<      none      >] vfs_fallocate+0x15a/0x230 fs/open.c:320
  [<     inline     >] SYSC_fallocate fs/open.c:343
  [<      none      >] SyS_fallocate+0x48/0x80 fs/open.c:337
  [<      none      >] entry_SYSCALL_64_fastpath+0x1f/0xc2 
/home/rzwisler/project/linux/arch/x86/entry/entry_64.S:204
  RIP: 0033:0x7f34dc4ff0ca
  RSP: 002b:00007ffcffa58058 EFLAGS: 00000246 ORIG_RAX: 000000000000011d
  RAX: ffffffffffffffda RBX: 0000000000000166 RCX: 00007f34dc4ff0ca
  RDX: 00000000000ba000 RSI: 0000000000000020 RDI: 0000000000000003
  RBP: 0000000000000003 R08: 000000000000007b R09: 00007ffcffa5807c
  R10: 00000000000bc000 R11: 0000000000000246 R12: 00007f34d8000de0
  R13: 00000000ffffffff R14: 000000000000af4a R15: 0000000000000000
  ---[ end trace e24f5d4cbfc216f6 ]---

This trace is with the current linux/master:

commit 926af6273fc6 ("Merge 
git://git.kernel.org/pub/scm/linux/kernel/git/davem/net")

though I initially his this issue with a v4.9 kernel.  My test setup is a pair
of PMEM ramdisks made with the memmap command line parameter, and my
test filesystem is mounted with DAX.

This can be reproduced pretty easily by just running generic/270 in a
loop.

Thanks,
- Ross