Re: lockdep warning for iscsi in 2.6.33-rc6

[Mike Christie]

On 02/09/2010 06:42 PM, Tao Ma wrote:
> Hi Mike,
>
> Mike Christie wrote:
> > On 02/09/2010 12:59 AM, Tao Ma wrote:
> > > Hi Mike,
> > > I meet with a lockdep warning for iscsi in 2.6.33-rc6.
> > > the lockdep is attached.
> >
> > If the lockdep output is saying that there is a problem with the iscsi
> > host taking its mutex then the scsi host mutex, I think that might be
> > a mistake in the lockdep detection. We always take the iscsi host
> > mutex then take the scsi host mutex.
> >
> > Could it get confused if we are scanning two hosts at the same time?
> > If it is just looking at if a lock is being taken then it would look
> > like host1 has its ihost->mutex and then took its shost->mutex, but
> > then host2 could start to get scanned at the same time, and it is
> > going to take its ihost->mutex. It would then look like we are trying
> > to grab a ihost->mutex while holding a shost->mutex. However, the
> > mutexs are not global and they are different instances of the mutex
> > because each host has its own.
> If these 2 mutexes are grabed in the same order(in your description,
> ihost->mutex first and then shost->mutex), there would be no problem.

I checked the code and we are taking the locks in the proper order, but 
I did some more testing and I do not think it was detecting what I 
thought above.

I just did a login with one iscsi session and got the lockdep warning. 
So I will do some more digging into what is going on.
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