Debugging rw lock
Alfred Perlstein
bright at mu.org
Thu Feb 13 21:02:42 UTC 2014
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.
-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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