linux-kernel - Re: [syzbot] [mm?] KCSAN: data-race in try_to_migrate_one / zap_page_range

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Message-ID: <4a061ceb-8504-43ae-b1eb-a5ab43811de7@iencinas.com>
Date: Sat, 15 Mar 2025 12:52:55 +0100
From: Ignacio Encinas Rubio <ignacio@...cinas.com>
To: syzbot+419c4b42acc36c420ad3@...kaller.appspotmail.com
Cc: akpm@...ux-foundation.org, hughd@...gle.com,
 linux-kernel@...r.kernel.org, linux-mm@...ck.org,
 syzkaller-bugs@...glegroups.com, linux-kernel-mentees@...ts.linux.dev,
 skhan@...uxfoundation.org
Subject: Re: [syzbot] [mm?] KCSAN: data-race in try_to_migrate_one /
 zap_page_range_single

Hello!

This seems like a recurrent complaint from KCSAN (other examples are
[1], [2]). 

>From what I understand looking at the source code, imprecise reporting 
of the maximum resident set size is considered to be acceptable.

Annotating `hiwater_rss` as `__data_racy` [3] should make KCSAN happy. 
Would this be an acceptable change? Another possibility would be making 
the update from `update_hiwater_rss` atomic, but it doesn't seem worth 
the potential slowdown.

Let me know if my proposal works for you.

Thanks!

[1] https://syzkaller.appspot.com/bug?extid=73d65fc86d6338db5990
[2] https://syzkaller.appspot.com/bug?extid=31cd52ba68feee156393
[3] https://docs.kernel.org/dev-tools/kcsan.html#selective-analysis