Subject: Re: About the try to remove cross-release feature entirely by Ingo
From: Byungchul Park <byungchul.park@lge.com>
To: Theodore Ts'o <tytso@mit.edu>,
        Matthew Wilcox <willy@infradead.org>,
        Byungchul Park <max.byungchul.park@gmail.com>,
        Thomas Gleixner <tglx@linutronix.de>,
        Peter Zijlstra <peterz@infradead.org>,
        Ingo Molnar <mingo@kernel.org>, david@fromorbit.com,
        Linus Torvalds <torvalds@linux-foundation.org>,
        Amir Goldstein <amir73il@gmail.com>,
        linux-kernel@vger.kernel.org, linux-mm@kvack.org,
        linux-block@vger.kernel.org, linux-fsdevel@vger.kernel.org,
        oleg@redhat.com, kernel-team@lge.com, daniel@ffwll.ch
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 <20171230154041.GB3366@thunk.org>
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 <f2bc220a-a363-122a-dbf9-e5416c550899@lge.com>
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Message-ID: <45973bf8-f20c-ec0c-7e82-71b4d0a64998@lge.com>
Date: Wed, 3 Jan 2018 17:23:07 +0900
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On 1/3/2018 5:10 PM, Byungchul Park wrote:
> On 1/3/2018 4:05 PM, Theodore Ts'o wrote:
>> On Wed, Jan 03, 2018 at 11:10:37AM +0900, Byungchul Park wrote:
>>>> The point I was trying to drive home is that "all we have to do is
>>>> just classify everything well or just invalidate the right lock
>>>
>>> Just to be sure, we don't have to invalidate lock objects at all but
>>> a problematic waiter only.
>>
>> So essentially you are proposing that we have to play "whack-a-mole"
>> as we find false positives, and where we may have to put in ad-hoc
>> plumbing to only invalidate "a problematic waiter" when it's
>> problematic --- or to entirely suppress the problematic waiter
> 
> If we have too many problematic completions(waiters) to handle it,
> then I agree with you. But so far, only one exits and it seems able
> to be handled even in the future on my own.
> 
> Or if you believe that we have a lot of those kind of completions
> making trouble so we cannot handle it, the (4) by Amir would work,
> no? I'm asking because I'm really curious about your opinion..
> 
>> altogether.  And in that case, a file system developer might be forced
>> to invalidate a lock/"waiter"/"completion" in another subsystem.
> 
> As I said, with regard to the invalidation, we don't have to
> consider locks at all. It's enough to invalidate the waiter only.
> 
>> I will also remind you that doing this will trigger a checkpatch.pl
>> *error*:
> 
> This is what we decided. And I think the decision is reasonable for
> original lockdep. But I wonder if we should apply the same decision
> on waiters. I don't insist but just wonder.

What if we adopt the (4) in which waiters are validated one by one
and no explicit invalidation is involved?

>> ERROR("LOCKDEP", "lockdep_no_validate class is reserved for 
>> device->mutex.\n" . $herecurr);
>>
>>                                       - Ted
>>
> 

-- 
Thanks,
Byungchul