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

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Date:   Mon, 11 Apr 2022 17:07:38 -0400
From:   Waiman Long <longman@...hat.com>
To:     john.p.donnelly@...cle.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 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