Re: [Xen-devel] [PATCH 0/4] enhance lock debugging

[Andrew Cooper <andrew.cooper3@xxxxxxxxxx>]

On 08/08/2019 05:50, Juergen Gross wrote:
> On 07.08.19 20:11, Andrew Cooper wrote:
>>
>> <snip>
>> Its not exactly the easiest to dump to follow.
>>
>> First of all - I don't see why the hold/block time are printed like
>> that.  It
>> might be a holdover from the 32bit build, pre PRId64 support.  They
>> should
>> probably use PRI_stime anyway.
>
> Fine with me.
>
>> The domid rendering is unfortunate.  Ideally we'd use %pd but that would
>> involve rearranging the logic to get a struct domain* in hand. 
>> Seeing as
>> you're the last person to modify this code, how hard would that be to
>> do?
>
> It would completely break the struct type agnostic design.

Ok.  As an alternatively, how about %pdr which takes a raw domid?  It
would be a trivial adjustment in the vsnprintf code, and could plausibly
be useful elsewhere where we have a domid and not a domain pointer.

>
> I have a debug patch adding credit2 run-queue lock. It requires to just
> add 5 lines of code (and this includes moving the spinlock_init() out of
> an irq-off section). It will produce:
>
> (XEN) credit2-runq 0 lock: addr=ffff830413351010, lockval=de00ddf, cpu=6
> (XEN)   lock: 896287(00000000:00FAA6B2), block:  819(00000000:00009C80)

What is the 0 here?

>
>> We have several global locks called lock:
>>
>>    (XEN) Global lock: addr=ffff82d0808181e0, lockval=10001, cpu=4095
>>    (XEN)   lock:           1(00000000:01322165), block:           
>> 0(00000000:00000000)
>>    (XEN) Global lock: addr=ffff82d080817cc0, lockval=100010, cpu=4095
>>    (XEN)   lock:           0(00000000:00000000), block:           
>> 0(00000000:00000000)
>>    (XEN) Global lock: addr=ffff82d080817800, lockval=0000, cpu=4095
>>    (XEN)   lock:           0(00000000:00000000), block:           
>> 0(00000000:00000000)
>>    (XEN) Global lock: addr=ffff82d080817780, lockval=0000, cpu=4095
>>    (XEN)   lock:           0(00000000:00000000), block:           
>> 0(00000000:00000000)
>>    (XEN) Global lock: addr=ffff82d080817510, lockval=0000, cpu=4095
>>    (XEN)   lock:           0(00000000:00000000), block:           
>> 0(00000000:00000000)
>>
>> The second one in particular has corrupt data, seeing has it has been
>> taken
>> and released several times without lock_cnt increasing.
>
> The lock might have been taken/released before lock profiling has been
> initialized.

What is there to initialise?  It all looks statically set up.

>
>> For sanity sake, we should enforce unique naming of any lock
>> registered for
>> profiling.
>
> This would be every lock inited via DEFINE_SPINLOCK(). I can do a
> followup patch for that purpose.

I was wondering how to do this.  One option which comes to mind is to
put an non-static object into .discard.lock_profile or something, so the
linker will object to repeated symbol names and then throw all of them away.

~Andrew

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