From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754680Ab1JXKCL (ORCPT ); Mon, 24 Oct 2011 06:02:11 -0400 Received: from mx1.redhat.com ([209.132.183.28]:5329 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754644Ab1JXKCK (ORCPT ); Mon, 24 Oct 2011 06:02:10 -0400 Date: Mon, 24 Oct 2011 12:02:39 +0200 From: "Michael S. Tsirkin" To: Rusty Russell Cc: Tejun Heo , virtualization@lists.linux-foundation.org, kvm@vger.kernel.org, linux-kernel@vger.kernel.org, Jens Axboe , Greg Kroah-Hartman Subject: Re: [PATCH 1/1] [virt] virtio-blk: Use ida to allocate disk index Message-ID: <20111024100238.GA27444@redhat.com> References: <1306913069-23637-1-git-send-email-dwu@redhat.com> <87mxi1xfz0.fsf@rustcorp.com.au> <4DEF744D.9040702@redhat.com> <87mxhrgba6.fsf@rustcorp.com.au> <20110609091433.GB11773@htj.dyndns.org> <4DF0A374.6090504@redhat.com> <20111019101220.GE25794@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20111019101220.GE25794@redhat.com> User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Oct 19, 2011 at 12:12:20PM +0200, Michael S. Tsirkin wrote: > 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 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 > > >>> 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 > > 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 > > Acked-by: Michael S. Tsirkin > > 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? Rusty, any opinion on merging this for 3.2? I expect merge window will open right after the summit, so need to decide soon ... > > --- > > 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 > > #include > > #include > > +#include > > > > #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 > > > > -- > > To unsubscribe from this list: send the line "unsubscribe kvm" in > > the body of a message to majordomo@vger.kernel.org > > More majordomo info at http://vger.kernel.org/majordomo-info.html