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    SubjectRe: [PATCHSET] mempool, percpu, blkcg: fix percpu stat allocation and remove stats_lock
    On Thu, Feb 23, 2012 at 03:12:04PM -0800, Tejun Heo wrote:
    > On Thu, Feb 23, 2012 at 03:01:23PM -0800, Tejun Heo wrote:
    > > Hmmm... going through the thread again, ah, okay, I forgot about that
    > > completely. Yeah, that is an actual problem. Both __GFP_WAIT which
    > > isn't GFP_KERNEL and GFP_KERNEL are valid use cases. I guess we'll be
    > > building async percpu pool in blkcg then. Great. :(
    >
    > Vivek, you win. :) Can you please refresh the async alloc patch on top
    > of blkcg-stacking branch? I'll rool that into this series and drop
    > the mempool stuff.

    Hi Tejun,

    Looks like there is one more issue. After booting kernel, I tried to read
    one of the cgroup files.

    cat /sys/fs/cgroup/blkio/blkio.throttle.read_bps_device and it oopses.

    Basically it looks like that we are getting a null dev pointer while we
    do following.

    dev_name(blkg->q->backing_dev_info.dev);

    I put some printk to verify backing_dev_info.dev is null. That means
    somehow we have a request queue and we did not call add_disk() on that?

    I checked that queue is not in bypass mode or dead mode. So nobody called
    blk_cleanup_queue() on that.

    Thanks
    Vivek

    chilli.lab.bos.redhat.com login: [ 62.090238] Vivek: q =
    ffff880136d647a0 bypass=0 dead=0
    [ 62.091001] Vivek: dev = ffff880138959520
    [ 62.091001] Vivek: q = ffff880136d623d0 bypass=0 dead=0
    [ 62.091001] Vivek: dev = (null)
    [ 62.091001] BUG: unable to handle kernel NULL pointer dereference at
    0000000000000050
    [ 62.091001] IP: [<ffffffff813091b5>] blkio_print_group_conf+0x85/0x160
    [ 62.091001] PGD 131757067 PUD 130915067 PMD 0
    [ 62.091001] Oops: 0000 [#1] SMP DEBUG_PAGEALLOC
    [ 62.091001] CPU 2
    [ 62.091001] Modules linked in: floppy [last unloaded: scsi_wait_scan]
    [ 62.091001]
    [ 62.091001] Pid: 4787, comm: cat Tainted: G W
    3.3.0-rc3-tejun-misc+ #13 Hewlett-Packard HP xw6600 Workstation/0A9Ch
    [ 62.091001] RIP: 0010:[<ffffffff813091b5>] [<ffffffff813091b5>]
    blkio_print_group_conf+0x85/0x160
    [ 62.091001] RSP: 0018:ffff8801315a9df8 EFLAGS: 00010096
    [ 62.091001] RAX: 0000000000000030 RBX: 0000000000000000 RCX:
    0000000000006867
    [ 62.091001] RDX: 0000000000000000 RSI: 0000000000000001 RDI:
    ffffffff81038af5
    [ 62.091001] RBP: ffff8801315a9e28 R08: 0000000000000002 R09:
    0000000000000000
    [ 62.091001] R10: 0000000000000001 R11: 0000000000000000 R12:
    0000000000000001
    [ 62.091001] R13: 0000000000010000 R14: ffff880137a9b480 R15:
    ffff880130a4c248
    [ 62.091001] FS: 00007ff3882f6720(0000) GS:ffff88013fc80000(0000)
    knlGS:0000000000000000
    [ 62.091001] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
    [ 62.091001] CR2: 0000000000000050 CR3: 0000000138b0a000 CR4:
    00000000000006e0
    [ 62.091001] DR0: 0000000000000000 DR1: 0000000000000000 DR2:
    0000000000000000
    [ 62.091001] DR3: 0000000000000000 DR6: 00000000ffff0ff0 DR7:
    0000000000000400
    [ 62.091001] Process cat (pid: 4787, threadinfo ffff8801315a8000, task
    ffff8801386ce840)
    [ 62.091001] Stack:
    [ 62.091001] ffff8801315a9e28 ffff880137a9b7e0 ffffffff81e45fc0
    ffff880130a4c248
    [ 62.091001] ffffffff81e46aa8 0000000000000000 ffff8801315a9e58
    ffffffff813092ff
    [ 62.091001] ffff88013167a580 ffff880130a4c248 0000000000000001
    ffff88013167a580
    [ 62.091001] Call Trace:
    [ 62.091001] [<ffffffff813092ff>] blkiocg_file_read+0x6f/0xd0
    [ 62.091001] [<ffffffff810aa240>] cgroup_seqfile_show+0x50/0x60
    [ 62.091001] [<ffffffff81174741>] seq_read+0x131/0x3f0
    [ 62.091001] [<ffffffff8114ee70>] vfs_read+0xb0/0x180
    [ 62.091001] [<ffffffff8114ef8a>] sys_read+0x4a/0x90
    [ 62.091001] [<ffffffff81843952>] system_call_fastpath+0x16/0x1b
    [ 62.091001] Code: 05 48 c1 ea 06 83 e2 01 83 e1 01 e8 dd 51 52 00 48 8b
    03 48 c7 c7 57 bc c9 81 48 8b 98 a8 05 00 00 31 c0 48 89 de e8 c2 51 52 00
    <48> 8b 53 50 48 85 d2 74 7a 45 85 e4 75 25 41 8b 4e 08 85 c9 75
    [ 62.091001] RIP [<ffffffff813091b5>] blkio_print_group_conf+0x85/0x160
    [ 62.091001] RSP <ffff8801315a9df8>
    [ 62.091001] CR2: 0000000000000050
    [ 62.091001] ---[ end trace be53af9706c0e89c ]---



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