Date: Fri, 14 Feb 2014 11:47:46 +0800 From: Julian Elischer <julian@freebsd.org> To: Alfred Perlstein <bright@mu.org>, Vijay Singh <vijju.singh@gmail.com> Cc: hackers@freebsd.org Subject: Re: Debugging rw lock Message-ID: <52FD91E2.4080903@freebsd.org> In-Reply-To: <52FD32FF.70106@mu.org> References: <CALCNsJS6vFJU18F3VRR-T2RdtGNxd3fycUCkQ63BmGp29DAUMw@mail.gmail.com> <52FD30D9.6050604@mu.org> <CALCNsJQzeqGh%2BZ0rW2jw9e%2BDfKdaRo9BpOQq7XrjfZ1EzNDFYQ@mail.gmail.com> <52FD32FF.70106@mu.org>
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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@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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>
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