linux-kernel - Re: [PATCH] perf: Fix sibling iteration

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Message-ID: <20180316103129.GC4064@hirez.programming.kicks-ass.net>
Date:   Fri, 16 Mar 2018 11:31:29 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     Alexey Budankov <alexey.budankov@...ux.intel.com>
Cc:     tglx@...utronix.de, Dmitry.Prohorov@...el.com,
        alexander.shishkin@...ux.intel.com, acme@...hat.com,
        mark.rutland@....com, linux-kernel@...r.kernel.org, hpa@...or.com,
        jolsa@...hat.com, torvalds@...ux-foundation.org, mingo@...nel.org,
        vincent.weaver@...ne.edu, kan.liang@...el.com, eranian@...gle.com,
        davidcc@...gle.com, valery.cherepennikov@...el.com,
        linux-tip-commits@...r.kernel.org
Subject: Re: [PATCH] perf: Fix sibling iteration

On Fri, Mar 16, 2018 at 12:59:34PM +0300, Alexey Budankov wrote:
> Hi,
> On 15.03.2018 20:01, Peter Zijlstra wrote:
> > Subject: perf: Fix sibling iteration
> > From: Peter Zijlstra <peterz@...radead.org>
> > Date: Thu Mar 15 17:36:56 CET 2018
> > 
> > Mark noticed that the change to sibling_list changed some iteration
> > semantics; because previously we used group_list as list entry,
> > sibling events would always have an empty sibling_list.
> > 
> > But because we now use sibling_list for both list head and list entry,
> > siblings will report as having siblings.
> > 
> > Fix this with a custom for_each_sibling_event() iterator.
> > 
> > Suggested-by: Mark Rutland <mark.rutland@....com>
> > Reported-by: Mark Rutland <mark.rutland@....com>
> > Fixes: 8343aae66167 ("perf/core: Remove perf_event::group_entry")
> > Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
> > ---
> 
> Applied to tip repo and run testing on Fedora 27/x86_64 (client skylake 8 cores):

There is at least one more known issue with that patch, but neither Mark
nor me could reproduce so far, so we don't know if we're right about the
cause.