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    SubjectRe: [PATCH 1/1] [virt] virtio-blk: Use ida to allocate disk index
    On Thu, Jun 09, 2011 at 06:41:56AM -0400, Mark Wu wrote:
    > On 06/09/2011 05:14 AM, Tejun Heo wrote:
    > > Hello,
    > >
    > > On Thu, Jun 09, 2011 at 08:51:05AM +0930, Rusty Russell wrote:
    > >> On Wed, 08 Jun 2011 09:08:29 -0400, Mark Wu <dwu@redhat.com> wrote:
    > >>> Hi Rusty,
    > >>> Yes, I can't figure out an instance of disk probing in parallel either, but as
    > >>> per the following commit, I think we still need use lock for safety. What's your opinion?
    > >>>
    > >>> commit 4034cc68157bfa0b6622efe368488d3d3e20f4e6
    > >>> Author: Tejun Heo <tj@kernel.org>
    > >>> Date: Sat Feb 21 11:04:45 2009 +0900
    > >>>
    > >>> [SCSI] sd: revive sd_index_lock
    > >>>
    > >>> Commit f27bac2761cab5a2e212dea602d22457a9aa6943 which converted sd to
    > >>> use ida instead of idr incorrectly removed sd_index_lock around id
    > >>> allocation and free. idr/ida do have internal locks but they protect
    > >>> their free object lists not the allocation itself. The caller is
    > >>> responsible for that. This missing synchronization led to the same id
    > >>> being assigned to multiple devices leading to oops.
    > >>
    > >> I'm confused. Tejun, Greg, anyone can probes happen in parallel?
    > >>
    > >> If so, I'll have to review all my drivers.
    > >
    > > Unless async is explicitly used, probe happens sequentially. IOW, if
    > > there's no async_schedule() call, things won't happen in parallel.
    > > That said, I think it wouldn't be such a bad idea to protect ida with
    > > spinlock regardless unless the probe code explicitly requires
    > > serialization.
    > >
    > > Thanks.
    > >
    > Since virtio blk driver doesn't use async probe, it needn't use spinlock to protect ida.
    > So remove the lock from patch.
    >
    > >From fbb396df9dbf8023f1b268be01b43529a3993d57 Mon Sep 17 00:00:00 2001
    > From: Mark Wu <dwu@redhat.com>
    > Date: Thu, 9 Jun 2011 06:34:07 -0400
    > Subject: [PATCH 1/1] [virt] virtio-blk: Use ida to allocate disk index
    >
    > Current index allocation in virtio-blk is based on a monotonically
    > increasing variable "index". It could cause some confusion about disk
    > name in the case of hot-plugging disks. And it's impossible to find the
    > lowest available index by just maintaining a simple index. So it's
    > changed to use ida to allocate index via referring to the index
    > allocation in scsi disk.
    >
    > Signed-off-by: Mark Wu <dwu@redhat.com>

    Acked-by: Michael S. Tsirkin <mst@redhat.com>

    This got lost in the noise and missed 3.1 which is unfortunate.
    How about we apply this as is and look at cleanups as a next step?

    > ---
    > drivers/block/virtio_blk.c | 28 +++++++++++++++++++++++-----
    > 1 files changed, 23 insertions(+), 5 deletions(-)
    >
    > diff --git a/drivers/block/virtio_blk.c b/drivers/block/virtio_blk.c
    > index 079c088..bf81ab6 100644
    > --- a/drivers/block/virtio_blk.c
    > +++ b/drivers/block/virtio_blk.c
    > @@ -8,10 +8,13 @@
    > #include <linux/scatterlist.h>
    > #include <linux/string_helpers.h>
    > #include <scsi/scsi_cmnd.h>
    > +#include <linux/idr.h>
    >
    > #define PART_BITS 4
    >
    > -static int major, index;
    > +static int major;
    > +static DEFINE_IDA(vd_index_ida);
    > +
    > struct workqueue_struct *virtblk_wq;
    >
    > struct virtio_blk
    > @@ -23,6 +26,7 @@ struct virtio_blk
    >
    > /* The disk structure for the kernel. */
    > struct gendisk *disk;
    > + u32 index;
    >
    > /* Request tracking. */
    > struct list_head reqs;
    > @@ -343,12 +347,23 @@ static int __devinit virtblk_probe(struct virtio_device *vdev)
    > struct request_queue *q;
    > int err;
    > u64 cap;
    > - u32 v, blk_size, sg_elems, opt_io_size;
    > + u32 v, blk_size, sg_elems, opt_io_size, index;
    > u16 min_io_size;
    > u8 physical_block_exp, alignment_offset;
    >
    > - if (index_to_minor(index) >= 1 << MINORBITS)
    > - return -ENOSPC;
    > + do {
    > + if (!ida_pre_get(&vd_index_ida, GFP_KERNEL))
    > + return -ENOMEM;
    > + err = ida_get_new(&vd_index_ida, &index);
    > + } while (err == -EAGAIN);
    > +
    > + if (err)
    > + return err;
    > +
    > + if (index_to_minor(index) >= 1 << MINORBITS) {
    > + err = -ENOSPC;
    > + goto out_free_index;
    > + }
    >
    > /* We need to know how many segments before we allocate. */
    > err = virtio_config_val(vdev, VIRTIO_BLK_F_SEG_MAX,
    > @@ -421,7 +436,7 @@ static int __devinit virtblk_probe(struct virtio_device *vdev)
    > vblk->disk->private_data = vblk;
    > vblk->disk->fops = &virtblk_fops;
    > vblk->disk->driverfs_dev = &vdev->dev;
    > - index++;
    > + vblk->index = index;
    >
    > /* configure queue flush support */
    > if (virtio_has_feature(vdev, VIRTIO_BLK_F_FLUSH))
    > @@ -516,6 +531,8 @@ out_free_vq:
    > vdev->config->del_vqs(vdev);
    > out_free_vblk:
    > kfree(vblk);
    > +out_free_index:
    > + ida_remove(&vd_index_ida, index);
    > out:
    > return err;
    > }
    > @@ -538,6 +555,7 @@ static void __devexit virtblk_remove(struct virtio_device *vdev)
    > mempool_destroy(vblk->pool);
    > vdev->config->del_vqs(vdev);
    > kfree(vblk);
    > + ida_remove(&vd_index_ida, vblk->index);
    > }
    >
    > static const struct virtio_device_id id_table[] = {
    > --
    > 1.7.1
    >
    > --
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