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

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Date:   Thu, 12 Jan 2017 17:16:43 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     Byungchul Park <byungchul.park@....com>
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 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.