Re: [PATCH 4/4] lockdep: Fix workqueue crossrelease annotation

[Byungchul Park]

On Wed, Aug 30, 2017 at 8:25 PM, Byungchul Park <byungchul.park@xxxxxxx> wrote:
> On Wed, Aug 30, 2017 at 06:24:39PM +0900, Byungchul Park wrote:
>> > -----Original Message-----
>> > From: Peter Zijlstra [mailto:peterz@xxxxxxxxxxxxx]
>> > Sent: Wednesday, August 30, 2017 6:12 PM
>> > To: Byungchul Park
>> > Cc: mingo@xxxxxxxxxx; tj@xxxxxxxxxx; boqun.feng@xxxxxxxxx;
>> > david@xxxxxxxxxxxxx; johannes@xxxxxxxxxxxxxxxx; oleg@xxxxxxxxxx; linux-
>> > kernel@xxxxxxxxxxxxxxx; kernel-team@xxxxxxx
>> > Subject: Re: [PATCH 4/4] lockdep: Fix workqueue crossrelease annotation
>> >
>> > On Wed, Aug 30, 2017 at 06:01:59PM +0900, Byungchul Park wrote:
>> > > My point is that we inevitably lose valuable dependencies by yours.
>> > That's
>> > > why I've endlessly asked you 'do you have any reason you try those
>> > patches?'
>> > > a ton of times. And you have never answered it.
>> >
>> > The only dependencies that are lost are those between the first work and
>> > the setup of the workqueue thread.
>> >
>> > And there obviously _should_ not be any dependencies between those. A
>>
>> 100% right. Since there obviously should not be any, it would be better
>> to check them. So I've endlessly asked you 'do you have any reason removing
>> the opportunity for that check?'. Overhead? Logical problem? Or want to
>> believe workqueue setup code perfect forever? I mean, is it a problem if we
>> check them?
>>
>> > work should not depend on the setup of the thread.
>>
>> 100% right.
>
> For example - I'm giving you the same example repeatedly:
>
> context X                 context Y
> ---------                 ---------
>                           wait_for_completion(C)
> acquire(A)
> process_one_work()
>    acquire(B)
>    work->fn()
>       complete(C)
>
> Please check C->A and C->B.

s/check/let lockdep check/


-- 
Thanks,
Byungchul