From nobody Sat Feb 7 21:23:44 2026 Received: from mail-wm1-f49.google.com (mail-wm1-f49.google.com [209.85.128.49]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 0BF431B1417 for ; Wed, 14 Aug 2024 14:53:08 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=209.85.128.49 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1723647190; cv=none; b=MTjM8/EpkpwwWujtV1/8UEre6UudJv4+EvaRVXC+Lr46phcNF6FklLlCmIFybbw4wjK4J8s/nS0RNSb2JxGS9fRQcpF1f/kRhiP1aqZhmB1hK/O+AEpiMeTU8FOXvJqgJ/o/ZxvrQzIIoflpuebG3BF1op52p0w4DrEIvo3+j9w= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1723647190; c=relaxed/simple; bh=f/oHoC9VpN5nx1mUCbmuS6hMWVT9zH2JfixxV6pSWCE=; h=From:To:Cc:Subject:Date:Message-ID:MIME-Version; b=d3/RENrxDd9Re0Xa8f/Jge/JizNKr2Bzd8PKzhzqLgYux4qQncaZVrm+3biyLvhMWgTXgaWeom/15DEkAYk3hTE5+2zirQZFTBuuZLQ7xJZo/WOOlSw3mQwqcraSiHKCXUPPwR2CKee3nGefMrCC0+sXOa1RZblbHHshtmyPXSo= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=gmail.com; spf=pass smtp.mailfrom=gmail.com; dkim=pass (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b=cR2babAB; arc=none smtp.client-ip=209.85.128.49 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=gmail.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=gmail.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b="cR2babAB" Received: by mail-wm1-f49.google.com with SMTP id 5b1f17b1804b1-4280bbdad3dso49851805e9.0 for ; Wed, 14 Aug 2024 07:53:08 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20230601; t=1723647187; x=1724251987; darn=vger.kernel.org; h=content-transfer-encoding:mime-version:message-id:date:subject:cc :to:from:from:to:cc:subject:date:message-id:reply-to; bh=lonJxsA8Fw6wOOZai80Q9J+BZK2m7M/vz+HKB4hoGGA=; b=cR2babAB9UllUXoZNt9yb7bLYiVgW3RTm9qBBs8o7UAzgsT6WqNdbJyPoeBHGnKEyJ xBkbUwPv7+XcxtiAZvSIQIus9vdQyNvWOJqDNF25mydb0mAon2Sy4PgP5twruehs5wxj QUIngfYzZNroFFbmP9iVv3/6LZWi2RSl83VFAMafXpjcpk0hFdzIc14h6XmJH1/svF+3 vwzY6pDXFtf4DxVsPgsJwUAIgOxTFT00aiwhmPrgo3R8oygzGshi/Zv7YH58EVfvaagI DyLqQCob2KzBzwD79IChaelABsVmoAQdNprMq4wuWitjcfd51iPxSCYRpjCJDLDg1U1V sRMQ== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1723647187; x=1724251987; h=content-transfer-encoding:mime-version:message-id:date:subject:cc :to:from:x-gm-message-state:from:to:cc:subject:date:message-id :reply-to; bh=lonJxsA8Fw6wOOZai80Q9J+BZK2m7M/vz+HKB4hoGGA=; b=gdZpXiPiy7oeFdfQiuw6m/CvKwEF0Y9w5gxWYFLOU2a/n/4xlx4hzP8s7aQ0AR22bF 0Cs7i8fYe43e6QYIRYK6cu4+KUUwhhJyB2KpLTGhHL5pOHqLjkssHs5XmoLWoYb5XFm0 gTFOUlSNvz8Bo3+erFZw3W1Kp6OAtq649TR6M7XB2QXnGip5bkrv5vA2/TdkaXTZ/VxK G+k5/OtuDcwg0QpB4nbSxMkPyOOzzp2q2ZsHqI+Jo0CVdMHjaNIKo9YGhZlmthqYqa2/ T3XRk86jfPRoc1L1eGoEI1XxrI81gigQTFunQDIFg+SRMHYamNc79rm1miqP/rWuEtjU Vi+g== X-Forwarded-Encrypted: i=1; AJvYcCWVstNQs4laGWwyAiIyIW/4lJ+QgrhJmtGLTGa83YC+tRUWR6pbJSDC0hrAAXZYSheLiiaYnRfMghDk4lvcmCG0zJMrTI05mdHuqa88 X-Gm-Message-State: AOJu0Yyc47tYg7AcjSdEOrGuB0lKgSoMZ8Gk+cpJIHhW24QUzwaISfZ4 GvIVGHrKMKjDM1Bzk9NDTTXBf0vGtpJ7HoTk8QJnZ1cgSvxLXtGuqnaWPK2Z X-Google-Smtp-Source: AGHT+IEoJbkP+hVe6+RzMKd+SJql/ELhAn+tPz0Gyw1HW0cOooFceTJ11Wl9zFZCSz+VoMQDguNnNQ== X-Received: by 2002:adf:e546:0:b0:368:77f9:fb34 with SMTP id ffacd0b85a97d-37177763876mr2346397f8f.15.1723647186881; Wed, 14 Aug 2024 07:53:06 -0700 (PDT) Received: from f.. (cst-prg-76-86.cust.vodafone.cz. [46.135.76.86]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-36e4e51ebefsm13003576f8f.89.2024.08.14.07.53.03 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 14 Aug 2024 07:53:05 -0700 (PDT) From: Mateusz Guzik To: akpm@linux-foundation.org, npiggin@gmail.com Cc: david@redhat.com, willy@infradead.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, Mateusz Guzik Subject: [PATCH] mm: whack now bogus comment in pmd_install() concerning a fence Date: Wed, 14 Aug 2024 16:52:56 +0200 Message-ID: <20240814145256.1683498-1-mjguzik@gmail.com> X-Mailer: git-send-email 2.43.0 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" Commit 362a61ad6119 ("fix SMP data race in pagetable setup vs walking") added the following: + smp_wmb(); /* Could be smp_wmb__xxx(before|after)_spin_lock */ + spin_lock(&mm->page_table_lock); However, over the years the fence along with the comment got moved around the file, eventually landing in a spot where it is *NOT* followed by a lock acquire (or any other operation which might happen to provide any fence on a given arch), rendering the comment stale. Signed-off-by: Mateusz Guzik --- ./scripts/get_maintainer.pl only showed akpm@ and the lists, adding the --git switch showed more names, but I only picked some of them. I don't know who makes the most sense to add here. I fully concede I could not be arsed to check if the fence is still needed to begin with, I ran into this while looking at something else. The comment puzzled me for a minute suggesting pmd_populate has an immediate lock acquire inside. mm/memory.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/mm/memory.c b/mm/memory.c index 34f8402d2046..0a6893833fac 100644 --- a/mm/memory.c +++ b/mm/memory.c @@ -436,7 +436,7 @@ void pmd_install(struct mm_struct *mm, pmd_t *pmd, pgta= ble_t *pte) * seen in-order. See the alpha page table accessors for the * smp_rmb() barriers in page table walking code. */ - smp_wmb(); /* Could be smp_wmb__xxx(before|after)_spin_lock */ + smp_wmb(); pmd_populate(mm, pmd, *pte); *pte =3D NULL; } --=20 2.43.0