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    SubjectRe: [1/6] 2.6.21-rc4: known regressions


    On Sun, 18 Mar 2007, Adrian Bunk wrote:
    >
    > Subject : weird system hangs
    > References : http://lkml.org/lkml/2007/3/16/288
    > Submitter : Michal Piotrowski <michal.k.k.piotrowski@gmail.com>
    > Mariusz Kozlowski <m.kozlowski@tuxland.pl>
    > Status : unknown

    According to the console log, it seems to be hung because a lot of
    processes are stuck in D state in various variations of this:

    Call Trace:
    [<c01ba134>] start_this_handle+0x2d7/0x355
    [<c01ba265>] journal_start+0xb3/0xe1
    [<c01b2837>] ext3_journal_start_sb+0x48/0x4a
    [<c01b0924>] ext3_create+0x47/0xe2
    [<c017820c>] vfs_create+0xcd/0x13e
    [<c017ab6e>] open_namei+0x176/0x5b5
    [<c0170026>] do_filp_open+0x26/0x3b
    [<c017007e>] do_sys_open+0x43/0xc2
    [<c0170135>] sys_open+0x1c/0x1e
    [<c0104064>] syscall_call+0x7/0xb

    and then you have "kget" (whatever that is) which is doing

    Call Trace:
    [<c0318981>] schedule_timeout+0x70/0x8e
    [<c03189b4>] schedule_timeout_uninterruptible+0x15/0x17
    [<c01b964a>] journal_stop+0xe2/0x1e6
    [<c01ba2b0>] journal_force_commit+0x1d/0x1f
    [<c01b29fb>] ext3_force_commit+0x22/0x24
    [<c01ad607>] ext3_write_inode+0x34/0x3a
    [<c0189f74>] __writeback_single_inode+0x1c5/0x2cb
    [<c018a096>] sync_inode+0x1c/0x2e
    [<c01a9ff7>] ext3_sync_file+0xab/0xc0
    [<c018c8c5>] do_fsync+0x4b/0x98
    [<c018c932>] __do_fsync+0x20/0x2f
    [<c018c951>] sys_fdatasync+0x10/0x12
    [<c0104064>] syscall_call+0x7/0xb

    with kjournald in D sleep at

    [<c01bb7b2>] journal_commit_transaction+0x15d/0x11d3
    [<c01bfcbe>] kjournald+0xab/0x1e8
    [<c01333dd>] kthread+0xb5/0xe0
    [<c0104cd3>] kernel_thread_helper+0x7/0x10

    which certainly looks like something is waiting for an IO to finish.

    In contrast, the hang reported by Mariusz Kozlowski has a slightly
    different feel to it, but there's a tantalizing pattern in there too:

    http://www.ussg.iu.edu/hypermail/linux/kernel/0703.0/1243.html

    Call Trace:
    [<c03ec87e>] io_schedule+0x42/0x59
    [<c0184915>] sleep_on_buffer+0x8/0xc
    [<c03ed217>] __wait_on_bit+0x47/0x6c
    [<c03ed297>] out_of_line_wait_on_bit+0x5b/0x64
    [<c01848a8>] __wait_on_buffer+0x27/0x2d
    [<c01b4228>] journal_commit_transaction+0x707/0x127f
    [<c01b868b>] kjournald+0xac/0x1ed
    [<c0126af5>] kthread+0xa2/0xc9
    [<c010422b>] kernel_thread_helper+0x7/0x1c

    which certainly also looks like an IO never completed (or completed but
    never woke anything up).

    It also seems to be related to *buffers*. Maybe the whole bh layer thing
    is a fluke, but it's not waiting for normal data, it's very much waiting
    for those journal things that all use buffer heads.Which just makes me
    worry about those patches by Nick (which did come in through Andrew). I
    don't think it's the memorder one (it looks safe and shouldn't matter on
    x86 anyway!), but what about the

    fs: fix __block_write_full_page error case buffer submission

    locking change for example? Or that "fs: fix nobh data leak" thing with
    its fix? It uses "SetPageUptodate(page);" without waking up anybody who
    might wait for it (but the waiters here seem to wait on buffers, so that's
    probably not it)..

    Alternatively, maybe it really is an _io_ problem (and the buffer-head
    thing is just a red herring, and it could happen to other IO, it's just
    that metadata IO uses buffer heads), and it's the scheduler changes since
    2.6.20..

    Jens, Nick.. Could you take a look?

    Linus
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