linux-kernel - Re: [PATCH v2] mm/vmscan: fix data races at kswapd_classzone

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Message-Id: <8C6CE0C4-7B15-41D5-A1B2-F48F6241200F@lca.pw>
Date:   Wed, 26 Feb 2020 06:50:01 -0500
From:   Qian Cai <cai@....pw>
To:     Matthew Wilcox <willy@...radead.org>
Cc:     akpm@...ux-foundation.org, elver@...gle.com, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] mm/vmscan: fix data races at kswapd_classzone_idx

> On Feb 25, 2020, at 11:06 PM, Matthew Wilcox <willy@...radead.org> wrote:
> 
> I don't understand why the usages of kswapd_classzone_idx in kswapd() and
> kswapd_try_to_sleep() don't need changing too?  kswapd_classzone_idx()
> looks safe to me, but I'm prone to missing stupid things that compilers
> are allowed to do.

I am not sure. Although it looks possible on paper, I am wondering why KCSAN did not trigger it yet which seems rather common. I did stress testing those areas with KCSAN for a few months now, but it might just be that I missed the report at the first place.

I’ll keep running some testing to confirm it, but until that happens or someone else could confirm it could happen, I’ll leave it out for this version. We can always submit an incremental patch later if necessary.