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    Subject[75/85] md: check ->hot_remove_disk when removing disk
    2.6.33-longterm review patch.  If anyone has any objections, please let us know.

    ------------------

    From: Namhyung Kim <namhyung@gmail.com>

    commit 01393f3d5836b7d62e925e6f4658a7eb22b83a11 upstream.

    Check pers->hot_remove_disk instead of pers->hot_add_disk in slot_store()
    during disk removal. The linear personality only has ->hot_add_disk and
    no ->hot_remove_disk, so that removing disk in the array resulted to
    following kernel bug:

    $ sudo mdadm --create /dev/md0 --level=linear --raid-devices=4 /dev/loop[0-3]
    $ echo none | sudo tee /sys/block/md0/md/dev-loop2/slot
    BUG: unable to handle kernel NULL pointer dereference at (null)
    IP: [< (null)>] (null)
    PGD c9f5d067 PUD 8575a067 PMD 0
    Oops: 0010 [#1] SMP
    CPU 2
    Modules linked in: linear loop bridge stp llc kvm_intel kvm asus_atk0110 sr_mod cdrom sg

    Pid: 10450, comm: tee Not tainted 3.0.0-rc1-leonard+ #173 System manufacturer System Product Name/P5G41TD-M PRO
    RIP: 0010:[<0000000000000000>] [< (null)>] (null)
    RSP: 0018:ffff880085757df0 EFLAGS: 00010282
    RAX: ffffffffa00168e0 RBX: ffff8800d1431800 RCX: 000000000000006e
    RDX: 0000000000000001 RSI: 0000000000000002 RDI: ffff88008543c000
    RBP: ffff880085757e48 R08: 0000000000000002 R09: 000000000000000a
    R10: 0000000000000000 R11: ffff88008543c2e0 R12: 00000000ffffffff
    R13: ffff8800b4641000 R14: 0000000000000005 R15: 0000000000000000
    FS: 00007fe8c9e05700(0000) GS:ffff88011fa00000(0000) knlGS:0000000000000000
    CS: 0010 DS: 0000 ES: 0000 CR0: 000000008005003b
    CR2: 0000000000000000 CR3: 00000000b4502000 CR4: 00000000000406e0
    DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
    DR3: 0000000000000000 DR6: 00000000ffff0ff0 DR7: 0000000000000400
    Process tee (pid: 10450, threadinfo ffff880085756000, task ffff8800c9f08000)
    Stack:
    ffffffff8138496a ffff8800b4641000 ffff88008543c268 0000000000000000
    ffff8800b4641000 ffff88008543c000 ffff8800d1431868 ffffffff81a78a90
    ffff8800b4641000 ffff88008543c000 ffff8800d1431800 ffff880085757e98
    Call Trace:
    [<ffffffff8138496a>] ? slot_store+0xaa/0x265
    [<ffffffff81384bae>] rdev_attr_store+0x89/0xa8
    [<ffffffff8115a96a>] sysfs_write_file+0x108/0x144
    [<ffffffff81106b87>] vfs_write+0xb1/0x10d
    [<ffffffff8106e6c0>] ? trace_hardirqs_on_caller+0x111/0x135
    [<ffffffff81106cac>] sys_write+0x4d/0x77
    [<ffffffff814fe702>] system_call_fastpath+0x16/0x1b
    Code: Bad RIP value.
    RIP [< (null)>] (null)
    RSP <ffff880085757df0>
    CR2: 0000000000000000
    ---[ end trace ba5fc64319a826fb ]---

    Signed-off-by: Namhyung Kim <namhyung@gmail.com>
    Signed-off-by: NeilBrown <neilb@suse.de>
    Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

    ---
    drivers/md/md.c | 2 +-
    1 file changed, 1 insertion(+), 1 deletion(-)

    --- a/drivers/md/md.c
    +++ b/drivers/md/md.c
    @@ -2386,7 +2386,7 @@ slot_store(mdk_rdev_t *rdev, const char
    if (rdev->raid_disk == -1)
    return -EEXIST;
    /* personality does all needed checks */
    - if (rdev->mddev->pers->hot_add_disk == NULL)
    + if (rdev->mddev->pers->hot_remove_disk == NULL)
    return -EINVAL;
    err = rdev->mddev->pers->
    hot_remove_disk(rdev->mddev, rdev->raid_disk);



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