linux-kernel - Re: [PATCH-tip v3 02/14] locking/rwsem: Make owner available even if !CONFIG_RWSEM_SPIN_ON

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Date:   Fri, 12 Apr 2019 10:07:09 -0400
From:   Waiman Long <longman@...hat.com>
To:     Ingo Molnar <mingo@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>
Cc:     Ingo Molnar <mingo@...hat.com>, Will Deacon <will.deacon@....com>,
        Thomas Gleixner <tglx@...utronix.de>,
        linux-kernel@...r.kernel.org, x86@...nel.org,
        Davidlohr Bueso <dave@...olabs.net>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Tim Chen <tim.c.chen@...ux.intel.com>,
        huang ying <huang.ying.caritas@...il.com>
Subject: Re: [PATCH-tip v3 02/14] locking/rwsem: Make owner available even if
 !CONFIG_RWSEM_SPIN_ON_OWNER

On 04/12/2019 10:04 AM, Waiman Long wrote:
> On 04/12/2019 03:09 AM, Ingo Molnar wrote:
>> * Peter Zijlstra <peterz@...radead.org> wrote:
>>
>>> On Fri, Apr 12, 2019 at 09:02:09AM +0200, Ingo Molnar wrote:
>>>> * Waiman Long <longman@...hat.com> wrote:
>>>>
>>>>> On 04/11/2019 04:12 AM, Peter Zijlstra wrote:
>>>>>> On Wed, Apr 10, 2019 at 02:42:19PM -0400, Waiman Long wrote:
>>>>>>> The owner field in the rw_semaphore structure is used primarily for
>>>>>>> optimistic spinning. However, identifying the rwsem owner can also be
>>>>>>> helpful in debugging as well as tracing locking related issues when
>>>>>>> analyzing crash dump. The owner field may also store state information
>>>>>>> that can be important to the operation of the rwsem.
>>>>>>>
>>>>>>> So the owner field is now made a permanent member of the rw_semaphore
>>>>>>> structure irrespective of CONFIG_RWSEM_SPIN_ON_OWNER.
>>>>>> sem->owner is still initialized under CONFIG_RWSEM_SPIN_ON_OWNER.
>>>>> Oh, you are right. I missed that part. I will fix it in the next version.
>>>> Could you please post the next series against tip:WIP.locking/core, which 
>>>> is already being dogfood-ed in -tip and which I'm running on my desktop? 
>>>> I'll backmerge any fixes as needed/requested.
>>> Urgh, please no, that's going to be hell to review :/
>> Ok - full patches then. I'll handle the fallout.
>>
>> Thanks,
>>
>> 	Ingo
> I will post an updated patchset later today.
>
> Sorry for the omission.
>
> Cheers,
> Longman
>
BTW, the v3 patch that I posted yesterday should work fine as long as
CONFIG_RWSEM_SPIN_ON_OWNER is defined.

Cheers,
Longman