On Sun, Jun 5, 2016 at 1:32 PM,  [off-list ref] wrote:

From: Mike Christie <redacted>

This patch drops the compat definition of req_op where it matches
the rq_flag_bits definitions, and drops the related old and compat
code that allowed users to set either the op or flags for the operation.

We also then store the operation in the bi_rw/cmd_flags field similar
to how we used to store the bio ioprio where it sat in the upper bits
of the field.

Signed-off-by: Mike Christie <redacted>

I was doing some xfstests testing yesterday using linux/master, and
hit a kernel BUG that bisected to this change.  The failing test is
generic/008 + ext2, without DAX.  This BUG reproduces with this test
100% as of this change, and 0% with the previous commit.

Here's the kernel commit that I bisected to:

commit 4e1b2d52a80d79296a5d899d73249748dea71a53
Author: Mike Christie [off-list ref]
Date:   Sun Jun 5 14:32:22 2016 -0500

block, fs, drivers: remove REQ_OP compat defs and related code

Here are the steps to reproduce the BUG using a pair of 1 GiB BRD ramdisks:

SCRATCH_DEV=/dev/ram0
TEST_DEV=/dev/ram1
mkfs.ext2 -F $SCRATCH_DEV
mkfs.ext2 -F $TEST_DEV
cd ~/xfstests
./check generic/008

Here is the BUG output for that commit, passed through
kasan_symbolize.py.  The line numbers are for the commit listed above,
not for linux/master:

 run fstests generic/008 at 2016-08-03 09:54:56
page:ffffea0017af04c0 count:3 mapcount:0 mapping:ffff8805eb059200 index:0x0
flags: 0x3fff8000002828(uptodate|lru|private|writeback)
page dumped because: VM_BUG_ON_PAGE(!PageLocked(page))
page->mem_cgroup:ffff8806098e0800
------------[ cut here ]------------
kernel BUG at mm/filemap.c:833!
invalid opcode: 0000 [#1] SMP
Modules linked in: brd dax_pmem nd_pmem dax nd_btt nd_e820 libnvdimm
CPU: 0 PID: 2522 Comm: xfs_io Not tainted 4.7.0-rc2-00042-g4e1b2d52 #18
Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS
rel-1.9.1-0-gb3ef39f-prebuilt.qemu-project.org 04/01/2014
task: ffff8805ebae4ec0 ti: ffff8805eba3c000 task.ti: ffff8805eba3c000
RIP: 0010:[<ffffffff811de115>] [<ffffffff811de115>] unlock_page+0xa5/0xb0
RSP: 0018:ffff8805eba3fa60 EFLAGS: 00010282
RAX: 0000000000000021 RBX: 0000000000000000 RCX: 0000000000000006
RDX: 0000000000000000 RSI: 0000000000000001 RDI: ffff8806109ce200
RBP: ffff8805eba3fa60 R08: 0000000000000001 R09: 0000000000000001
R10: ffff8805ebae4ec0 R11: 0000000000000001 R12: ffffea0017af04c0
R13: 0000000000028000 R14: ffffffffa00202c0 R15: ffff88060eff1200
FS: 00007f87a31cf700(0000) GS:ffff880610800000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007f87a31e6000 CR3: 000000060da31000 CR4: 00000000001406f0
Stack:
ffff8805eba3fa98 ffffffff812bd782 ffff8805eba3fdb0 0000000000001000
ffffea0017af04c0 0000000000000000 0000000000000088 ffff8805eba3fbe0
ffffffff812c3ff1 ffff8805eba3fd00 0000000000028000 0000000c00000000
Call Trace:
[<ffffffff812bd782>] bdev_write_page+0xb2/0xe0 fs/block_dev.c:462
[<ffffffff812c3ff1>] __mpage_writepage+0x5c1/0x750 fs/mpage.c:604
[<ffffffff811eedbd>] write_cache_pages+0x20d/0x5f0 mm/page-writeback.c:2261
[<ffffffff812c3955>] mpage_writepages+0x75/0xe0 fs/mpage.c:703
[<ffffffff8137951b>] ext2_writepages+0x3b/0x40 fs/ext2/inode.c:887
[<ffffffff811f27a1>] do_writepages+0x21/0x30 mm/page-writeback.c:2361
[<ffffffff811e1396>] __filemap_fdatawrite_range+0xc6/0x100 mm/filemap.c:300
[<ffffffff811e1514>] filemap_write_and_wait_range+0x44/0x90 mm/filemap.c:490
[<ffffffff812a7707>] __generic_file_fsync+0x27/0x90 fs/libfs.c:937
[<ffffffff812a7789>] generic_file_fsync+0x19/0x40 fs/libfs.c:974
[<ffffffff81377e9e>] ext2_fsync+0x2e/0x70 fs/ext2/file.c:149
[<ffffffff812b549b>] vfs_fsync_range+0x4b/0xb0 fs/sync.c:195
[< inline >] vfs_fsync fs/sync.c:209
[<ffffffff812b555d>] do_fsync+0x3d/0x70 fs/sync.c:219
[< inline >] SYSC_fsync fs/sync.c:227
[<ffffffff812b5810>] SyS_fsync+0x10/0x20 fs/sync.c:225
[<ffffffff81acd33c>] entry_SYSCALL_64_fastpath+0x1f/0xbd
arch/x86/entry/entry_64.S:207
Code: 00 00 48 d3 ea 89 d2 48 8d 0c 92 48 8d 14 4a 48 8d 3c d0 31 d2
e8 bc fc f1 ff 5d c3 48 c7 c6 20 1d ec 81 4c 89 c7 e8 bb 8d 03 00 <0f>
0b 66 0f 1f 84 00 00 00 00 00 66 66 66 66 90 55 b9 08 00 00
RIP [<ffffffff811de115>] unlock_page+0xa5/0xb0 mm/filemap.c:833
RSP <ffff8805eba3fa60>
---[ end trace d419bf59bba263fb ]---

I'm happy to provide any additional info you need, or to test fixes.

Thanks,
- Ross

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