linux-kernel - Re: [PATCH] kbuild: skip per-CPU BTF generation for pahole v1.18-v1.21

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Date:   Mon, 31 May 2021 10:34:23 +0100
From:   Mel Gorman <mgorman@...hsingularity.net>
To:     Andrii Nakryiko <andrii@...nel.org>
Cc:     akpm@...ux-foundation.org, bpf@...r.kernel.org, msuchanek@...e.de,
        linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        hritikxx8@...il.com, jolsa@...nel.org, kernel-team@...com,
        Arnaldo Carvalho de Melo <acme@...hat.com>,
        Hao Luo <haoluo@...gle.com>
Subject: Re: [PATCH] kbuild: skip per-CPU BTF generation for pahole
 v1.18-v1.21

On Sat, May 29, 2021 at 05:25:36PM -0700, Andrii Nakryiko wrote:
> Commit "mm/page_alloc: convert per-cpu list protection to local_lock"
> introduced a zero-sized per-CPU variable, which causes pahole to generate
> invalid BTF. Only pahole versions 1.18 through 1.21 are impacted, as before
> 1.18 pahole doesn't know anything about per-CPU variables, and 1.22 contains
> the proper fix for the issue.
> 
> Luckily, pahole 1.18 got --skip_encoding_btf_vars option disabling BTF
> generation for per-CPU variables in anticipation of some unanticipated
> problems. So use this escape hatch to disable per-CPU var BTF info on those
> problematic pahole versions. Users relying on availability of per-CPU var BTFs
> would need to upgrade to pahole 1.22+, but everyone won't notice any
> regressions.
> 
> Cc: Mel Gorman <mgorman@...hsingularity.net>
> Cc: Arnaldo Carvalho de Melo <acme@...hat.com>
> Cc: Hao Luo <haoluo@...gle.com>
> Signed-off-by: Andrii Nakryiko <andrii@...nel.org>

Acked-by: Mel Gorman <mgorman@...hsingularity.net>

-- 
Mel Gorman
SUSE Labs