linux-kernel - Re: [PATCH v4 05/15] lockdep: Make check_prev_add can use a separate stack

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Message-ID: <20170113024518.GB3326@X58A-UD3R>
Date:   Fri, 13 Jan 2017 11:45:18 +0900
From:   Byungchul Park <byungchul.park@....com>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     mingo@...nel.org, tglx@...utronix.de, walken@...gle.com,
        boqun.feng@...il.com, kirill@...temov.name,
        linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        iamjoonsoo.kim@....com, akpm@...ux-foundation.org,
        npiggin@...il.com
Subject: Re: [PATCH v4 05/15] lockdep: Make check_prev_add can use a separate
 stack_trace

On Thu, Jan 12, 2017 at 05:16:43PM +0100, Peter Zijlstra wrote:
> On Fri, Dec 09, 2016 at 02:12:01PM +0900, Byungchul Park wrote:
> > check_prev_add() saves a stack trace of the current. But crossrelease
> > feature needs to use a separate stack trace of another context in
> > check_prev_add(). So make it use a separate stack trace instead of one
> > of the current.
> > 
> 
> So I was thinking, can't we make check_prevs_add() create the stack
> trace unconditionally but record if we used it or not, and then return
> the entries when unused. All that is serialized by graph_lock anyway and
> that way we already pass a stack into check_prev_add() so we can easily
> pass in a different one.
> 
> I think that removes a bunch of tricky and avoids all the new tricky.

Looks very good.