even with Linus's set_page_dirty_lock() suggestion:

[  160.607904] EXT4-fs (loop0): mounted filesystem with ordered data mode. Opts: (null)
[  173.093239] ------------[ cut here ]------------
[  173.097884] kernel BUG at /home/davehans/linux.git/fs/ext4/inode.c:2377!
[  173.104695] invalid opcode: 0000 [#1] SMP 
[  173.108849] CPU: 65 PID: 4286 Comm: racewrite_threa Not tainted 3.15.0-rc2+ #392
[  173.116383] Hardware name: FUJITSU-SV PRIMEQUEST 1800E2/SB, BIOS PRIMEQUEST 1000 Series BIOS Version 1.24 09/14/2011
[  173.127174] task: ffff887ff1909140 ti: ffff887ff2048000 task.ti: ffff887ff2048000
[  173.134799] RIP: 0010:[<ffffffff81204810>]  [<ffffffff81204810>] mpage_prepare_extent_to_map+0x320/0x330
[  173.144432] RSP: 0018:ffff887ff2049c68  EFLAGS: 00010246
[  173.149819] RAX: 0000000000000041 RBX: ffff887ff2049dc8 RCX: ffff88bff2e52b48
[  173.157080] RDX: 6bfffc000002003d RSI: 0000000000000167 RDI: ffffffff819c1ce8
[  173.164341] RBP: ffff887ff2049d48 R08: ffffea037fbdb980 R09: 0000000000000001
[  173.171603] R10: 0000000000000000 R11: 0000000000000220 R12: 7fffffffffffffff
[  173.178864] R13: 0000000000000041 R14: ffff887ff2049ca8 R15: ffff887ff2049ca8
[  173.186125] FS:  00007fe361e37700(0000) GS:ffff88dfffaa0000(0000) knlGS:0000000000000000
[  173.194381] CS:  0010 DS: 0000 ES: 0000 CR0: 000000008005003b
[  173.200214] CR2: 00007fe3aa70a000 CR3: 0000005fefdd9000 CR4: 00000000000007e0
[  173.207475] Stack:
[  173.209506]  ffffea037fbdb980 ffff887ff2049ca8 ffff88bff2e52b48 0000000000000000
[  173.217017]  0000000000000000 0000000000000001 0000000000000000 ffffea037fbdb980
[  173.224527]  0000000000000003 0000000000000286 ffff887ff1909140 ffff883ff2730800
[  173.232038] Call Trace:
[  173.234527]  [<ffffffff81233fcc>] ? __ext4_journal_start_sb+0x7c/0x120
[  173.241159]  [<ffffffff8120af6b>] ? ext4_writepages+0x44b/0xce0
[  173.247166]  [<ffffffff8120afa4>] ext4_writepages+0x484/0xce0
[  173.253001]  [<ffffffff81123933>] do_writepages+0x23/0x40
[  173.258479]  [<ffffffff811165f9>] __filemap_fdatawrite_range+0x59/0x60
[  173.265112]  [<ffffffff8111b3f5>] SyS_fadvise64_64+0x265/0x270
[  173.271031]  [<ffffffff8111b40e>] SyS_fadvise64+0xe/0x10
[  173.276429]  [<ffffffff816d8a29>] system_call_fastpath+0x16/0x1b
[  173.282513] Code: ff e9 6d ff ff ff 48 8d bd 48 ff ff ff e8 b9 20 f2 ff e9 31 ff ff ff 48 8b 4b 08 8b 49 20 85 c9 0f 85 ee fd ff ff 31 c0 eb b3 90 <0f> 0b 0f 0b 66 66 66 2e 0f 1f 84 00 00 00 00 00 66 66 66 66 90 
[  173.301685] RIP  [<ffffffff81204810>] mpage_prepare_extent_to_map+0x320/0x330
[  173.308933]  RSP <ffff887ff2049c68>
[  173.312576] ---[ end trace b53fdf1d352b727a ]---