Re: [PATCH 1/1] [virt] virtio-blk: Use ida to allocate disk index

[Mark Wu]

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.