linux-kernel - Re: [PATCH 2/3] lockdep: Introduce lock_acquire

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Message-ID: <20170905072239.ggxalc2vrbpoyppr@hirez.programming.kicks-ass.net>
Date:   Tue, 5 Sep 2017 09:22:39 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Byungchul Park <byungchul.park@....com>
Cc:     tj@...nel.org, johannes.berg@...el.com, mingo@...nel.org,
        tglx@...utronix.de, oleg@...hat.com, david@...morbit.com,
        linux-kernel@...r.kernel.org, kernel-team@....com
Subject: Re: [PATCH 2/3] lockdep: Introduce lock_acquire_might()

On Tue, Sep 05, 2017 at 11:29:13AM +0900, Byungchul Park wrote:
> From the point of view of crossrelease, we can never be aware of the
> release context in advance, until we get to the lock_release().
> However, this way we cannot report deadlocks occured at the time.
> 
> Sometimes, we want to report that kind of problems, taking a risk
> generating false dependencies e.g. lock_acquire()s in workqueue code,
> which inevitably generate false ones with all acquisitions in works.
> 
> It would be better to provide another primitive, lock_acquire_might()
> for that purpose so that lockdep internal can be aware of what users
> expect and get chances to enhance to avoid false ones.
> 
> The primitive should:
> 
>    1. work as if it's trylock, since links between lock_acquire_might()
>       and later ones are only meaningful. Remind this should be used to
>       do what crossrelease commit does, in advance.
> 
>    2. make acquisitions by lock_acquire_might() ignored on the commit.
> 

Shees, talk about ugly... Also might-lock has a different meaning.