linux-kernel - Re: [PATCH v5] locking/rwsem: Make handoff bit handling more consistent

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Date:   Tue, 12 Apr 2022 11:28:58 -0500
From:   john.p.donnelly@...cle.com
To:     Waiman Long <longman@...hat.com>,
        chenguanyou <chenguanyou9338@...il.com>,
        gregkh@...uxfoundation.org
Cc:     dave@...olabs.net, hdanton@...a.com, linux-kernel@...r.kernel.org,
        mazhenhua@...omi.com, mingo@...hat.com, peterz@...radead.org,
        quic_aiquny@...cinc.com, will@...nel.org, sashal@...nel.org
Subject: Re: [PATCH v5] locking/rwsem: Make handoff bit handling more
 consistent

On 4/11/22 4:07 PM, Waiman Long wrote:
> 
> On 4/11/22 17:03, john.p.donnelly@...cle.com wrote:
>>
>>>>
>>>> I have reached out to Waiman and he suggested this for our next test 
>>>> pass:
>>>>
>>>>
>>>> 1ee326196c6658 locking/rwsem: Always try to wake waiters in 
>>>> out_nolock path
>>>
>>> Does this commit help to avoid the lockup problem?
>>>
>>> Commit 1ee326196c6658 fixes a potential missed wakeup problem when a 
>>> reader first in the wait queue is interrupted out without acquiring 
>>> the lock. It is actually not a fix for commit d257cc8cb8d5. However, 
>>> this commit changes the out_nolock path behavior of writers by 
>>> leaving the handoff bit set when the wait queue isn't empty. That 
>>> likely makes the missed wakeup problem easier to reproduce.
>>>
>>> Cheers,
>>> Longman
>>>
>>
>> Hi,
>>
>>
>> We are testing now
>>
>> ETA for fio soak test completion is  ~15hr from now.
>>
>> I wanted to share the stack traces for future reference + occurrences.
>>
> I am looking forward to your testing results tomorrow.
> 
> Cheers,
> Longman
> 
Hi

  Our 24hr fio soak test with :

  1ee326196c6658 locking/rwsem: Always try to wake waiters in out_nolock 
path


  applied to 5.15.30  passed.

  I suggest you append  1ee326196c6658 with :


  cc: stable

   Fixes: d257cc8cb8d5 ("locking/rwsem: Make handoff bit handling more 
consistent")


I'll leave the implementation details up to the core maintainers how to 
do that ;-)

...

Thank you

John.

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