linux-kernel - Re: [PATCH] mm, debug_pagealloc: don't rely on static keys too early

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Message-Id: <83B24C03-1484-4DD6-9B42-029FF1B27287@lca.pw>
Date:   Thu, 19 Dec 2019 08:16:59 -0500
From:   Qian Cai <cai@....pw>
To:     Vlastimil Babka <vbabka@...e.cz>
Cc:     Andrew Morton <akpm@...ux-foundation.org>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org, stable@...r.kernel.org,
        Joonsoo Kim <iamjoonsoo.kim@....com>,
        "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
        Michal Hocko <mhocko@...nel.org>,
        Matthew Wilcox <willy@...radead.org>,
        Mel Gorman <mgorman@...hsingularity.net>,
        Peter Zijlstra <peterz@...radead.org>,
        Borislav Petkov <bp@...en8.de>
Subject: Re: [PATCH] mm, debug_pagealloc: don't rely on static keys too early



> On Dec 19, 2019, at 8:06 AM, Vlastimil Babka <vbabka@...e.cz> wrote:
> 
> Commit 96a2b03f281d ("mm, debug_pagelloc: use static keys to enable debugging")
> has introduced a static key to reduce overhead when debug_pagealloc is compiled
> in but not enabled. It relied on the assumption that jump_label_init() is
> called before parse_early_param() as in start_kernel(), so when the
> "debug_pagealloc=on" option is parsed, it is safe to enable the static key.
> 
> However, it turns out multiple architectures call parse_early_param() earlier
> from their setup_arch(). x86 also calls jump_label_init() even earlier, so no
> issue was found while testing the commit, but same is not true for e.g. ppc64
> and s390 where the kernel would not boot with debug_pagealloc=on as found by
> our QA.

This was daily tested on linux-next here for those arches and never saw an issue. Are you able to reproduce it on mainline or linux-next?