Re: [PATCH v2] vfio: Follow a strict lifetime for struct iommu_group

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On 10/5/22 9:57 AM, Jason Gunthorpe wrote:
> On Wed, Oct 05, 2022 at 09:46:45AM -0400, Matthew Rosato wrote:
> 
>  
>> (again, with the follow-up applied) Besides the panic above I just
>> noticed there is also this warning that immediately precedes and is
>> perhaps more useful.  Re: what triggers the WARN, both group->owner
>> and group->owner_cnt are already 0
> 
> And this is after the 2nd try that fixes the locking?

Maybe I missed that email?  I've only seen one version, happy to try another.  Please resend?

> 
> This shows that vfio_group_detach_container() is called twice (which
> was my guess), hoever this looks to be impossible as both calls are
> protected by 'if (group->container)' and the function NULL's
> group->container and it is all under the proper lock.
> 
> My guess was that missing locking caused the two cases to race and
> trigger WARN, but the locking should fix that.
> 
> So I'm at a loss, can you investigate a bit?
> 
> Jason




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