On 2011-10-24 12:02, Michael S. Tsirkin wrote: > 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 <dwu@xxxxxxxxxx> 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@xxxxxxxxxx> >>>>>> 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@xxxxxxxxxx> >>> 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@xxxxxxxxxx> >> >> Acked-by: Michael S. Tsirkin <mst@xxxxxxxxxx> >> >> 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, I can toss it into for-3.2/drivers, if there's consensus to do that now. -- Jens Axboe -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
