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    SubjectRe: btrfs btree_ctree_super fault
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    On 11/08/2016 09:59 AM, Dave Jones wrote:
    > On Sun, Nov 06, 2016 at 11:55:39AM -0500, Dave Jones wrote:
    > > <subject changed, hopefully we're done with bio corruption for now>
    > >
    > > On Mon, Oct 31, 2016 at 01:44:55PM -0600, Chris Mason wrote:
    > > > On Mon, Oct 31, 2016 at 12:35:16PM -0700, Linus Torvalds wrote:
    > > > >On Mon, Oct 31, 2016 at 11:55 AM, Dave Jones <davej@codemonkey.org.uk> wrote:
    > > > >>
    > > > >> BUG: Bad page state in process kworker/u8:12 pfn:4e0e39
    > > > >> page:ffffea0013838e40 count:0 mapcount:0 mapping:ffff8804a20310e0 index:0x100c
    > > > >> flags: 0x400000000000000c(referenced|uptodate)
    > > > >> page dumped because: non-NULL mapping
    > > > >
    > > > >Hmm. So this seems to be btrfs-specific, right?
    > > > >
    > > > >I searched for all your "non-NULL mapping" cases, and they all seem to
    > > > >have basically the same call trace, with some work thread doing
    > > > >writeback and going through btrfs_writepages().
    > > > >
    > > > >Sounds like it's a race with either fallocate hole-punching or
    > > > >truncate. I'm not seeing it, but I suspect it's btrfs, since DaveJ
    > > > >clearly ran other filesystems too but I am not seeing this backtrace
    > > > >for anything else.
    > > >
    > > > Agreed, I think this is a separate bug, almost certainly btrfs specific.
    > > > I'll work with Dave on a better reproducer.
    > >
    > > Still refining my 'capture ftrace when trinity detects taint' feature,
    > > but in the meantime, here's a variant I don't think we've seen before:
    >
    > And another new one:
    >
    > kernel BUG at fs/btrfs/ctree.c:3172!
    > invalid opcode: 0000 [#1] PREEMPT SMP DEBUG_PAGEALLOC
    > CPU: 0 PID: 22702 Comm: trinity-c40 Not tainted 4.9.0-rc4-think+ #1
    > task: ffff8804ffde37c0 task.stack: ffffc90002188000
    > RIP: 0010:[<ffffffffa00576b9>]
    > [<ffffffffa00576b9>] btrfs_set_item_key_safe+0x179/0x190 [btrfs]
    > RSP: 0000:ffffc9000218b8a8 EFLAGS: 00010246
    > RAX: 0000000000000000 RBX: ffff8804fddcf348 RCX: 0000000000001000
    > RDX: 0000000000000000 RSI: ffffc9000218b9ce RDI: ffffc9000218b8c7
    > RBP: ffffc9000218b908 R08: 0000000000004000 R09: ffffc9000218b8c8
    > R10: 0000000000000000 R11: 0000000000000001 R12: ffffc9000218b8b6
    > R13: ffffc9000218b9ce R14: 0000000000000001 R15: ffff880480684a88
    > FS: 00007f7c7f998b40(0000) GS:ffff880507800000(0000) knlGS:0000000000000000
    > CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
    > CR2: 0000000000000000 CR3: 000000044f15f000 CR4: 00000000001406f0
    > DR0: 00007f4ce439d000 DR1: 0000000000000000 DR2: 0000000000000000
    > DR3: 0000000000000000 DR6: 00000000ffff0ff0 DR7: 0000000000000600
    > Stack:
    > ffff880501430000 d305ffffa00a2245 006c000000000002 0500000000000010
    > 6c000000000002d3 0000000000001000 000000006427eebb ffff880480684a88
    > 0000000000000000 ffff8804fddcf348 0000000000002000 0000000000000000
    > Call Trace:
    > [<ffffffffa009cff0>] __btrfs_drop_extents+0xb00/0xe30 [btrfs]

    We've been hunting this one for at least two years. It's the white
    whale of btrfs bugs. Josef has a semi-reliable reproducer now, but I
    think it's not the same as the pagevec based problems you reported earlier.

    -chris

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