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    SubjectRe: [PATCH 0/11] Per-bdi writeback flusher threads #4
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    On Tue, 2009-05-19 at 08:20 +0200, Jens Axboe wrote:
    > On Tue, May 19 2009, Zhang, Yanmin wrote:
    > > On Mon, 2009-05-18 at 14:19 +0200, Jens Axboe wrote:
    > > > Hi,
    > > >
    > > > This is the fourth version of this patchset. Chances since v3:
    > > >
    > > > - Dropped a prep patch, it has been included in mainline since.
    > > >
    > > > - Add a work-to-do list to the bdi. This is struct bdi_work. Each
    > > > wb thread will notice and execute work on bdi->work_list. The arguments
    > > > are which sb (or NULL for all) to flush and how many pages to flush.
    > > >
    > > > - Fix a bug where not all bdi's would end up on the bdi_list, so potentially
    > > > some data would not be flushed.
    > > >
    > > > - Make wb_kupdated() pass on wbc->older_than_this so we maintain the same
    > > > behaviour for kupdated flushes.
    > > >
    > > > - Have the wb thread flush first before sleeping, to avoid losing the
    > > > first flush on lazy register.
    > > >
    > > > - Rebase to newer kernels.

    > I'm attaching two patches - apply #1 to -rc6, and then #2 is a roll-up
    > of the patch series that you can apply next.
    Jens,

    I run into 2 issues with kernel 2.6.30-rc6+BDI_Flusher_V4. Below is one.

    Tue May 19 00:00:00 CST 2009
    BUG: unable to handle kernel NULL pointer dereference at 00000000000001d8
    IP: [<ffffffff803f3c4c>] generic_make_request+0x10a/0x384
    PGD 0
    Oops: 0000 [#1] SMP
    last sysfs file: /sys/block/sdb/stat
    CPU 0
    Modules linked in: igb
    Pid: 1445, comm: bdi-8:16 Not tainted 2.6.30-rc6-bdiflusherv4 #1 X8DTN
    RIP: 0010:[<ffffffff803f3c4c>] [<ffffffff803f3c4c>] generic_make_request+0x10a/0x384
    RSP: 0018:ffff8800bd04da60 EFLAGS: 00010206
    RAX: 0000000000000000 RBX: ffff8801be45d500 RCX: 00000000038a0df8
    RDX: 0000000000000008 RSI: 0000000000000576 RDI: ffff8801bf408680
    RBP: ffff8801be45d500 R08: ffffe20001ee8140 R09: ffff8800bd04da98
    R10: 0000000000000000 R11: ffff8800bd72eb40 R12: ffff8801be45d500
    R13: ffff88005f51f310 R14: 0000000000000008 R15: ffff8800b15a5458
    FS: 0000000000000000(0000) GS:ffffc20000000000(0000) knlGS:0000000000000000
    CS: 0010 DS: 0018 ES: 0018 CR0: 000000008005003b
    CR2: 00000000000001d8 CR3: 0000000000201000 CR4: 00000000000006e0
    DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
    DR3: 0000000000000000 DR6: 00000000ffff0ff0 DR7: 0000000000000400
    Process bdi-8:16 (pid: 1445, threadinfo ffff8800bd04c000, task ffff8800bd1b75f0)
    Stack:
    0000000000000008 ffffffff8027a613 00000000848dc000 ffffffffffffffff
    ffff8800a8190f50 ffffffff00000012 ffff8800a81938e0 ffffc2000000001b
    0000000000000000 0000000000000000 ffffe200026f9c30 0000000000000000
    Call Trace:
    [<ffffffff8027a613>] ? mempool_alloc+0x59/0x10f
    [<ffffffff803f3f70>] ? submit_bio+0xaa/0xb1
    [<ffffffff802c6a3f>] ? submit_bh+0xe3/0x103
    [<ffffffff802c92ea>] ? __block_write_full_page+0x1fb/0x2f2
    [<ffffffff802c7d6a>] ? end_buffer_async_write+0x0/0xfb
    [<ffffffff8027e8d2>] ? __writepage+0xa/0x25
    [<ffffffff8027f036>] ? write_cache_pages+0x21c/0x338
    [<ffffffff8027e8c8>] ? __writepage+0x0/0x25
    [<ffffffff8027f195>] ? do_writepages+0x27/0x2d
    [<ffffffff802c22c1>] ? __writeback_single_inode+0x159/0x2b3
    [<ffffffff8071e52a>] ? thread_return+0x3e/0xaa
    [<ffffffff8027f267>] ? determine_dirtyable_memory+0xd/0x1d
    [<ffffffff8027f2dd>] ? get_dirty_limits+0x1d/0x255
    [<ffffffff802c27bc>] ? generic_sync_wb_inodes+0x1b4/0x220
    [<ffffffff802c3130>] ? wb_do_writeback+0x16c/0x215
    [<ffffffff802c323e>] ? bdi_writeback_task+0x65/0x10d
    [<ffffffff8024cc06>] ? autoremove_wake_function+0x0/0x2e
    [<ffffffff8024cb27>] ? bit_waitqueue+0x10/0xa0
    [<ffffffff80289257>] ? bdi_start_fn+0x0/0xba
    [<ffffffff802892c6>] ? bdi_start_fn+0x6f/0xba
    [<ffffffff8024c860>] ? kthread+0x54/0x80
    [<ffffffff8020c97a>] ? child_rip+0xa/0x20
    [<ffffffff8024c80c>] ? kthread+0x0/0x80
    [<ffffffff8020c970>] ? child_rip+0x0/0x20
    The panic happened at the beginging of a mmap randrw after a mmap randwrite.

    It's triggered in __generic_make_request => bdev_get_queue(bio->bi_bdev),
    because bio->bi_bdev->bd_disk is equal to NULL.

    The callchain is:
    bdi_writeback_task =>
    wb_do_writeback =>
    generic_sync_wb_inodes =>
    __writeback_single_inode =>
    ...
    __block_write_full_page =>
    submit_bh =>
    submit_bio=>
    generic_make_request

    yanmin


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