Debugging rw lock

[Julian Elischer]

On 2/14/14, 5:02 AM, Alfred Perlstein wrote:
>
> On 2/13/14, 12:59 PM, Vijay Singh wrote:
>> You're talking about instrumenting the code, right? But which 
>> thread? I was
>> thinking of augmenting the rw lock to record the readers, but 
>> wanted to
>> check if something is possible without instrumentation.
>
> If rw locks are implemented using low level atomics then you're 
> going to make the very slow and have a LOT of work to do as opposed 
> to just using a thread specific storage to implement it. You're 
> better off just making use of the fact that only "curthread" can 
> access the per-thread stack and just use that.  Or at least that's 
> how it works in my brain.

maybe do it the other way around and count the read locks a thread 
has.. then when there is a problem go see what they hold..
(or add the ability to detail 10 locks each or something)
>
> -Alfred
>
>
>>
>>
>> On Thu, Feb 13, 2014 at 12:53 PM, Alfred Perlstein <bright at mu.org> 
>> wrote:
>>
>>> Keep a stack of rwlocks owned in the struct thread.
>>>
>>> -Alfred
>>>
>>> On 2/13/14, 12:51 PM, Vijay Singh wrote:
>>>
>>>> I am running into an issue where an rw lock is read locked and never
>>>> unlocked, and causes a system to livelock. I was wondering if its 
>>>> possible
>>>> to figure out which thread owns the read lock?
>>>>
>>>> It's the tcp pcbinfo lock.
>>>>
>>>> (kgdb-amd64-7.4-08) show_rwlock rw
>>>>    name : tcp
>>>>    class: rw
>>>>    flags: {SLEEP, INITED, WITNESS, RECURSE, UPGRADABLE}
>>>>    state: RLOCK: 1 locks
>>>>    waiters: writers
>>>>
>>>> Any help is appreciated.
>>>>
>>>> -vijay
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>
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