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    Subject[RFC PATCH] virtio_blk: Checking "private_data" to avoid kernel panic when hotplugging

    On guest with upstream's kernel(3.3.0-rc7), I
    mounted virtblk as:
    a) # mkfs /dev/vda
    b) # mount /dev/vda /mnt
    c) # cd /mnt

    Then I did hotplug for virtblk via virsh on host as:
    a) # sudo virsh detach-disk guest vda
    b) # sudo virsh attach-disk guest /media/data/test.img vda

    I encountered guest's kernel panic (*probability *
    *event*)whose backtrace liked this:

    PID: 2496 TASK: ffff88001f5de080 CPU: 0 COMMAND: "blkid"
    #0 [ffff88001afdbb00] machine_kexec at ffffffff81031fcb
    #1 [ffff88001afdbb60] crash_kexec at ffffffff810b8f72
    #2 [ffff88001afdbc30] oops_end at ffffffff814f04b0
    #3 [ffff88001afdbc60] die at ffffffff8100f26b
    #4 [ffff88001afdbc90] do_general_protection at ffffffff814f0042
    #5 [ffff88001afdbcc0] general_protection at ffffffff814ef815
    [exception RIP: virtio_check_driver_offered_feature+27]
    RIP: ffffffffa00540cb RSP: ffff88001afdbd78 RFLAGS: 00010206
    RAX: ffffffff810ffde0 RBX: ffff88001f14a800 RCX: 000000004cf0758b
    RDX: 4ce86d8b4ce0658b RSI: 0000000000000007 RDI: ffffffff81a970a0
    RBP: ffff88001afdbd78 R8: ffffffffa009d060 R9: 0000000000000100
    R10: 0000000000000006 R11: 0000000000000246 R12: 000000000000101d
    R13: 0000000000005331 R14: ffffffff81a970a0 R15: 0000000000000000
    ORIG_RAX: ffffffffffffffff CS: 0010 SS: 0018
    #6 [ffff88001afdbd80] virtblk_ioctl at ffffffffa009c459 [virtio_blk]
    #7 [ffff88001afdbdc0] __blkdev_driver_ioctl at ffffffff81257317
    #8 [ffff88001afdbe00] blkdev_ioctl at ffffffff8125779d
    #9 [ffff88001afdbe50] block_ioctl at ffffffff811aec5c
    #10 [ffff88001afdbe60] vfs_ioctl at ffffffff81189342
    #11 [ffff88001afdbea0] do_vfs_ioctl at ffffffff811894e4
    #12 [ffff88001afdbf30] sys_ioctl at ffffffff81189a61
    #13 [ffff88001afdbf80] system_call_fastpath at ffffffff8100b0f2
    RIP: 0000003f566dd847 RSP: 00007fffa23e6130 RFLAGS: 00010202
    RAX: 0000000000000010 RBX: ffffffff8100b0f2 RCX: 0000000000000008
    RDX: 0000000000000000 RSI: 0000000000005331 RDI: 0000000000000003
    RBP: 0000000040000000 R8: 0000003f5699b580 R9: 0000000000000100
    R10: 0000000000000006 R11: 0000000000000246 R12: 0000000000000000
    R13: 0000003f59020ba0 R14: 0000000000000003 R15: 000000000241f030
    ORIG_RAX: 0000000000000010 CS: 0033 SS: 002b

    This panic was triggered by the command of "blkid" in
    udev's rule "60-persistent-storage.rules".

    So, when the virtblk was reattached, command "blkid"
    probed filesystem metadata of disks. At that moment,
    virtblk_ioctl() was called, but the data of "virtio_blk"
    "bdev->bd_disk->private_data" pointing to may not be
    updated for the sync reason.

    This patch do this check to avoid panic.

    Any comment will be appreciated.

    Signed-off-by: Ren Mingxin <>
    virtio_blk.c | 6 ++++++
    1 file changed, 6 insertions(+)

    diff --git a/drivers/block/virtio_blk.c b/drivers/block/virtio_blk.c
    index c4a60ba..4ac81f8 100644
    --- a/drivers/block/virtio_blk.c
    +++ b/drivers/block/virtio_blk.c
    @@ -245,6 +245,12 @@ static int virtblk_ioctl(struct block_device *bdev,
    fmode_t mode,
    struct virtio_blk *vblk = disk->private_data;

    + * Check whether the private data pointer has been updated.
    + */
    + if (vblk != vblk->vdev->priv)
    + return -EFAULT;
    + /*
    * Only allow the generic SCSI ioctls if the host can support it.
    if (!virtio_has_feature(vblk->vdev, VIRTIO_BLK_F_SCSI))


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