From: Vlastimil Babka <vbabka@suse.cz>
To: Qian Cai <cai@lca.pw>
Cc: Andrew Morton <akpm@linux-foundation.org>,
linux-mm@kvack.org, linux-kernel@vger.kernel.org,
stable@vger.kernel.org, Joonsoo Kim <iamjoonsoo.kim@lge.com>,
"Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>,
Michal Hocko <mhocko@kernel.org>,
Matthew Wilcox <willy@infradead.org>,
Mel Gorman <mgorman@techsingularity.net>,
Peter Zijlstra <peterz@infradead.org>,
Borislav Petkov <bp@alien8.de>
Subject: Re: [PATCH] mm, debug_pagealloc: don't rely on static keys too early
Date: Thu, 19 Dec 2019 14:34:29 +0100 [thread overview]
Message-ID: <703d85ab-899c-8192-2618-995efc292fdb@suse.cz> (raw)
In-Reply-To: <83B24C03-1484-4DD6-9B42-029FF1B27287@lca.pw>
On 12/19/19 2:16 PM, Qian Cai wrote:
>
>
>> On Dec 19, 2019, at 8:06 AM, Vlastimil Babka <vbabka@suse.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.
Well I assume nobody has booted the kernel specifically with
debug_pagealloc=on. In case a randconfig run enabled
CONFIG_DEBUG_PAGEALLOC_ENABLE_DEFAULT then the problem wouldn't manifest
as the static key would be initialized with DEFINE_STATIC_KEY_TRUE by
the compiler itself, and the enabling-by-param would be a no-op.
> Are you able to reproduce it on mainline or linux-next?
I didn't try, but our kernel is 5.3-based so that's quite recent. The
offending commit was also introduced in 5.3-rc1 so there's that.
next prev parent reply other threads:[~2019-12-19 13:34 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-12-19 13:06 [PATCH] mm, debug_pagealloc: don't rely on static keys too early Vlastimil Babka
2019-12-19 13:16 ` Qian Cai
2019-12-19 13:34 ` Vlastimil Babka [this message]
2020-01-03 3:02 ` Andrew Morton
2020-01-06 8:37 ` Vlastimil Babka
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