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[24.6.216.183]) by smtp.gmail.com with ESMTPSA id h13-20020a170902680d00b00174d9bbeda4sm1627756plk.197.2022.10.29.12.28.34 (version=TLS1_2 cipher=ECDHE-ECDSA-AES128-GCM-SHA256 bits=128/128); Sat, 29 Oct 2022 12:28:35 -0700 (PDT) Content-Type: text/plain; charset=us-ascii Mime-Version: 1.0 (Mac OS X Mail 16.0 \(3696.120.41.1.1\)) Subject: Re: [PATCH 01/13] mm: Update ptep_get_lockless()s comment From: Nadav Amit In-Reply-To: Date: Sat, 29 Oct 2022 12:28:33 -0700 Cc: Peter Zijlstra , Jann Horn , John Hubbard , X86 ML , Matthew Wilcox , Andrew Morton , kernel list , Linux-MM , Andrea Arcangeli , "Kirill A . Shutemov" , jroedel@suse.de, ubizjak@gmail.com, Alistair Popple Content-Transfer-Encoding: quoted-printable Message-Id: References: <20221022111403.531902164@infradead.org> <20221022114424.515572025@infradead.org> <2c800ed1-d17a-def4-39e1-09281ee78d05@nvidia.com> <6C548A9A-3AF3-4EC1-B1E5-47A7FFBEB761@gmail.com> <47678198-C502-47E1-B7C8-8A12352CDA95@gmail.com> To: Linus Torvalds X-Mailer: Apple Mail (2.3696.120.41.1.1) ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1667071717; a=rsa-sha256; cv=none; b=fKKVKxxSlS5M5+GmtJPDzLCLNrIQQ7ZqvhrFrpvgoLCI9sGvIFgN1WPwrZvJkxOm5v8rt4 mn5Rqa7yYoXVUFg+vabQ9WZDA0p2ZmwgHzqr4qE+dF/YiTPPThVAzVyiUR9++CHz0bp36C CiA2jNhj0+9gFWSlzSsxACbVtUTIsO8= ARC-Authentication-Results: i=1; imf13.hostedemail.com; dkim=pass header.d=gmail.com header.s=20210112 header.b=YLn+7prP; spf=pass (imf13.hostedemail.com: domain of nadav.amit@gmail.com designates 209.85.214.174 as permitted sender) smtp.mailfrom=nadav.amit@gmail.com; dmarc=pass (policy=none) header.from=gmail.com ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1667071717; h=from:from:sender:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references:dkim-signature; bh=Z5MNM9Gp83rj3UXMtx0nvDXUik0Rl01o5B2bsdQaQS4=; b=xaYc1vBxM8pZAC9X0ek6GcTCYAp+X/euXVBGSJvfR83xHmFFW5fXDOjxl6EceiYVq7R/Zj A6Mw3qtl6mECKKKJV0YAQof7JMQGGbozwBljnEB5R5iN5Vp3uJpkZ6c7YbjLzokrpQ9XC2 G53wxfc+mE1ROh9hnFnda3Sz182oO9g= Authentication-Results: imf13.hostedemail.com; dkim=pass header.d=gmail.com header.s=20210112 header.b=YLn+7prP; spf=pass (imf13.hostedemail.com: domain of nadav.amit@gmail.com designates 209.85.214.174 as permitted sender) smtp.mailfrom=nadav.amit@gmail.com; dmarc=pass (policy=none) header.from=gmail.com X-Rspamd-Server: rspam05 X-Rspamd-Queue-Id: 9E5AA2000E X-Stat-Signature: n7n91cizxakwqo1m4yqhug466gkraq4t X-Rspam-User: X-HE-Tag: 1667071717-994524 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Oct 29, 2022, at 12:14 PM, Linus Torvalds = wrote: > On Sat, Oct 29, 2022 at 11:58 AM Linus Torvalds > wrote: >> Still not tested in any way, shape, or form. I decided I wanted to >> send this one before booting into this and possibly blowing up ;^) >=20 > Well, it boots, and I see no difference with your PoC code. >=20 > It didn't fail for me before, it doesn't fail for me with those = patches. >=20 > Again, the "it doesn't fail for me" is probably because I'm running it > incorrectly, although for all I know there can also be hardware > differences. Please give me some time to test it. I presume you ran it with block ram device (not tmpfs) and not on a virtual machine (which can affect = besides Intel/AMD implementation differences). But even if your patches work and the tests pass, I am not sure it means that everything is fine. I did not try to trigger a race with shrink_page_list(), and doing that might be harder than the race I tried = to create before. I need to do some tracing to understand what I was = missing in my understanding of the shrink_page_list() - assuming that I am mistaken about the buffers being potentially released. I would note that my concern about releasing the buffers is partially = driven by to issues that were reported before [1]. I am actually not sure how = they were resolved. [1] https://lore.kernel.org/all/20180103100430.GE4911@quack2.suse.cz/