kernel BUG at fs/ext4/extents.c:LINE!

[syzbot <syzbot+06c885be0edcdaeab40c@syzkaller.appspotmail.com>]

Hello,

syzbot hit the following crash on upstream commit
10b84daddbec72c6b440216a69de9a9605127f7a (Sat Mar 31 17:59:00 2018 +0000)
Merge branch 'perf-urgent-for-linus' of  
git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip
syzbot dashboard link:  
https://syzkaller.appspot.com/bug?extid=06c885be0edcdaeab40c

C reproducer: https://syzkaller.appspot.com/x/repro.c?id=6721172100087808
syzkaller reproducer:  
https://syzkaller.appspot.com/x/repro.syz?id=4701086711545856
Raw console output:  
https://syzkaller.appspot.com/x/log.txt?id=6392087410900992
Kernel config:  
https://syzkaller.appspot.com/x/.config?id=-2760467897697295172
compiler: gcc (GCC) 7.1.1 20170620

IMPORTANT: if you fix the bug, please add the following tag to the commit:
Reported-by: syzbot+06c885be0edcdaeab40c@syzkaller.appspotmail.com
It will help syzbot understand when the bug is fixed. See footer for  
details.
If you forward the report, please keep this part and the footer.

------------[ cut here ]------------
kernel BUG at fs/ext4/extents.c:3190!
invalid opcode: 0000 [#1] SMP KASAN
Dumping ftrace buffer:
    (ftrace buffer empty)
Modules linked in:
CPU: 0 PID: 4422 Comm: syzkaller152353 Not tainted 4.16.0-rc7+ #9
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS  
Google 01/01/2011
RIP: 0010:ext4_split_extent_at+0x75d/0x1160 fs/ext4/extents.c:3190
RSP: 0018:ffff8801c6b8e290 EFLAGS: 00010293
RAX: ffff8801acdc0080 RBX: ffff8801b425b018 RCX: ffffffff81e959ad
RDX: 0000000000000000 RSI: ffff8801a79c11f0 RDI: ffff8801d96ce940
RBP: ffff8801c6b8e3f8 R08: 0000000000000010 R09: 0000000000000425
R10: 0000000000000000 R11: 0000000000000000 R12: ffff8801d96ce930
R13: 0000000000003010 R14: 1ffff10038d71c5e R15: 0000000000000010
FS:  00000000014a2880(0000) GS:ffff8801db000000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007f8298ddf000 CR3: 00000001ad57f002 CR4: 00000000001606f0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Call Trace:
  ext4_split_extent.isra.36+0x2b6/0x490 fs/ext4/extents.c:3364
  ext4_ext_convert_to_initialized fs/ext4/extents.c:3619 [inline]
  ext4_ext_handle_unwritten_extents+0x1acd/0x3940 fs/ext4/extents.c:4081
  ext4_ext_map_blocks+0x12d1/0x4410 fs/ext4/extents.c:4339
  ext4_map_blocks+0xc90/0x1830 fs/ext4/inode.c:636
  mpage_map_one_extent fs/ext4/inode.c:2452 [inline]
  mpage_map_and_submit_extent fs/ext4/inode.c:2505 [inline]
  ext4_writepages+0x2035/0x3c30 fs/ext4/inode.c:2875
  do_writepages+0xff/0x170 mm/page-writeback.c:2340
  __filemap_fdatawrite_range+0x32f/0x460 mm/filemap.c:444
  file_write_and_wait_range+0x8a/0x100 mm/filemap.c:752
  ext4_sync_file+0x4fb/0x1260 fs/ext4/fsync.c:128
  vfs_fsync_range+0x110/0x260 fs/sync.c:196
  generic_write_sync include/linux/fs.h:2680 [inline]
  ext4_file_write_iter+0x919/0x10c0 fs/ext4/file.c:270
  call_write_iter include/linux/fs.h:1782 [inline]
  do_iter_readv_writev+0x55c/0x830 fs/read_write.c:653
  do_iter_write+0x154/0x540 fs/read_write.c:932
  vfs_iter_write+0x77/0xb0 fs/read_write.c:945
  iter_file_splice_write+0x7db/0xf30 fs/splice.c:749
  do_splice_from fs/splice.c:851 [inline]
  direct_splice_actor+0x125/0x180 fs/splice.c:1018
  splice_direct_to_actor+0x2c1/0x820 fs/splice.c:973
  do_splice_direct+0x29b/0x3c0 fs/splice.c:1061
  do_sendfile+0x5c9/0xe80 fs/read_write.c:1413
  SYSC_sendfile64 fs/read_write.c:1468 [inline]
  SyS_sendfile64+0xbd/0x160 fs/read_write.c:1460
  do_syscall_64+0x281/0x940 arch/x86/entry/common.c:287
  entry_SYSCALL_64_after_hwframe+0x42/0xb7
RIP: 0033:0x440029
RSP: 002b:00007fff87fd7e68 EFLAGS: 00000217 ORIG_RAX: 0000000000000028
RAX: ffffffffffffffda RBX: 00000fffffeff000 RCX: 0000000000440029
RDX: 0000000020000000 RSI: 0000000000000004 RDI: 0000000000000003
RBP: 00000000006cb018 R08: 00007fff87fd7e80 R09: 00007fff87fd7e80
R10: 0000000100000001 R11: 0000000000000217 R12: 0000000000401860
R13: 00000000004018f0 R14: 0000000000000000 R15: 0000000000000000
Code: fe ff ff 48 c7 c7 c0 9c 56 87 0f b7 43 08 4c 8d 04 40 49 c1 e0 04 49  
01 d8 e8 a0 66 ff ff 41 89 c7 e9 f8 fd ff ff e8 93 0b 88 ff <0f> 0b e8 8c  
0b 88 ff 48 8b 8d b8 fe ff ff 48 b8 00 00 00 00 00
RIP: ext4_split_extent_at+0x75d/0x1160 fs/ext4/extents.c:3190 RSP:  
ffff8801c6b8e290
---[ end trace d3416668281344cc ]---


---
This bug is generated by a dumb bot. It may contain errors.
See https://goo.gl/tpsmEJ for details.
Direct all questions to syzkaller@googlegroups.com.

syzbot will keep track of this bug report.
If you forgot to add the Reported-by tag, once the fix for this bug is  
merged
into any tree, please reply to this email with:
#syz fix: exact-commit-title
If you want to test a patch for this bug, please reply with:
#syz test: git://repo/address.git branch
and provide the patch inline or as an attachment.
To mark this as a duplicate of another syzbot report, please reply with:
#syz dup: exact-subject-of-another-report
If it's a one-off invalid bug report, please reply with:
#syz invalid
Note: if the crash happens again, it will cause creation of a new bug  
report.
Note: all commands must start from beginning of the line in the email body.