From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mail-qt1-f181.google.com (mail-qt1-f181.google.com [209.85.160.181]) (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 52BE933B943 for ; Wed, 21 Jan 2026 02:42:28 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=209.85.160.181 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1768963349; cv=none; b=SRv24EIciVS2XzyrOkMMiD2C1gf98gNxShBn/XUB9DeqeOpoOk41Oakhs/tZQlMQxlbHhPOmBZbFFWVs1s2o+Aroe1EceqhmujVSlckL7efTRtq5Ai4BVsT2KiOJUzV5x6Poo6RbHDhaFc0eef30i8UqsHISBlUcTMaUnKH5tUk= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1768963349; c=relaxed/simple; bh=YycTiJrPuZ50XWbU+aKf4d35PZCgfYUN6bofn1fuMIY=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=gTsGnR0fYAfk4C3LP8HCkvg1lHXKMlTcywxf5WaIcvEMeAe57xnfHPLqN7LeZoklGw6/93eZsYJbxaDTWTYpnSfIJgcqByjJOIQUlrAxwGjW39jKE0UNE00riVuEtZVhV/FwW5eUejEDDnK0Ifz6ibG4cr7w2EIfnCoIyapIZYw= 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=II1rYPhM; arc=none smtp.client-ip=209.85.160.181 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="II1rYPhM" Received: by mail-qt1-f181.google.com with SMTP id d75a77b69052e-5013c912f9fso69640451cf.2 for ; Tue, 20 Jan 2026 18:42:28 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20230601; t=1768963347; x=1769568147; darn=vger.kernel.org; h=in-reply-to:content-disposition:mime-version:references:message-id :subject:cc:to:from:date:feedback-id:from:to:cc:subject:date :message-id:reply-to; bh=/SYWzQFciEmh1FoU8deqlPVu+NRiIm4WLmRuTDTk8Qc=; b=II1rYPhMcZ46wyVJqfij0yXTXvO80PYXVWWxG1IHKPk4O8hL1aLhH1bXJZuVYvn3mU 4RGePfVgw+XuYnBiHQD15QxiDmG/QWERm77lWjll/EN9ginbMuOQ1P7nMfv+0J59MMu8 0DC2wrGRavYs17MDrf3p3c8YF2/pEs4h+W3y42Yg/1b2wgVMqxm54U1kxMVZ567RmnUl kamASaoZyXW+lSGQpl3lWlGnwi6b3yF5kSUebAmS70x2XJ/N+yTvEljSSSNMskp/Qimg V4TQSB3Id8jZyX8lSim423hpJhGB+0ipk+1OQL+IK1Tw/wI7gzbBp2HVoW1rjMVv5L9r DN7Q== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1768963347; x=1769568147; h=in-reply-to:content-disposition:mime-version:references:message-id :subject:cc:to:from:date:feedback-id:x-gm-gg:x-gm-message-state:from :to:cc:subject:date:message-id:reply-to; bh=/SYWzQFciEmh1FoU8deqlPVu+NRiIm4WLmRuTDTk8Qc=; b=re4UbnF3+jop0uLrsn7mQHyhh23C3ajFXqrSDW6LtCQ1tbe1vhGA1iOJDccuR8zF7t yfcDiY0bgYwaxLtGGul0lmGV+tH3tXBKmSckEY6rWKh85rFcmNvensApxD99T+Kl8AZe LdznL05pqZLitluB1ZP3RjMiOIT8H6+cDkbqL0LxXf0PeDdn45DgzsA2MHBF4QKgJyQS MtyhUe4gdv8hQxoTw92KFXh4Mk87uS845VLTcp3QDD5TkCkhQVkMeSim67hpSaN6rqNx 0vbAJOJga3s3oT2efZ/MY7BTSuAhe9vvoPMLAjeGQKxNccXOjK6D5VeiDyyHcBexLVXa RvaQ== X-Forwarded-Encrypted: i=1; AJvYcCXQccESkYIW/2CKJqjfpfspihV1wKxTIDY1Ni89UKGIPJu7q2H9eEioW4sGRNcEiwG8drj6Xj+MZlipOdenjg==@vger.kernel.org X-Gm-Message-State: AOJu0Yycx+LkKrlaoGEMUeFjEdy3enYX06GMum0e+thsWzQ7E0YHykOC 6anHd7+99hdcuV3vrurlUwg/dCvypyBcZahpTtXBhRhbaZJPhnEnFk5Wj4ZIf5uI X-Gm-Gg: AZuq6aLcI+E2B62RmTTDICEEaCJcBLB31FRSTNR/KuiPQfjZwvw9QGefsWkkOHOiDOO gRtuGcyCGMdBT5iV45hlDxLm+H/oLH9woOWo0ycnfkJAxmz8VsMVvvo6/cZT6Jwrn6yNEPXOVBC BsqihSjwGEkgiHJCo5LCmbPNAaS08Jh9OkjyX6QaTXR0vRzh8xlEuvrRoaodS7FiX9sHB8ePiHN a9ncNhAMTpKoVIYynv9vU5MghD/4yJVdu24ZQ/CbZGyuNhth9EB1kNOydZ3i/cswSRNw28wwDlW oD8UWtD4RL3yvT4yPQ6mhuopfbsLRQNrLSlweKgUlN7Jsohvu1+t+yMnUZa8Wwbbjyab+6bq1uX 4MYu9JvGjpz5NR1hmyDEXTVuyvAVpV87x0c0f992bNrx1Cn1FF9eehcFpJFzo4mfTIeS7nCfBe6 kTHtzOYKRV8b6xYp8ZIGTghFb7VnZke6Da4RqQen/4cGAKJcYEq8Zr6clRaJES89GmeJZJvbW0K zQiNGhB/q4oS5g= X-Received: by 2002:ac8:5e11:0:b0:4f4:d298:b47c with SMTP id d75a77b69052e-502a1e07becmr238961631cf.28.1768956457813; Tue, 20 Jan 2026 16:47:37 -0800 (PST) Received: from fauth-a1-smtp.messagingengine.com (fauth-a1-smtp.messagingengine.com. [103.168.172.200]) by smtp.gmail.com with ESMTPSA id af79cd13be357-8c6a7269277sm1143950785a.43.2026.01.20.16.47.36 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 20 Jan 2026 16:47:37 -0800 (PST) Received: from phl-compute-02.internal (phl-compute-02.internal [10.202.2.42]) by mailfauth.phl.internal (Postfix) with ESMTP id 9A38FF40070; Tue, 20 Jan 2026 19:47:35 -0500 (EST) Received: from phl-frontend-03 ([10.202.2.162]) by phl-compute-02.internal (MEProxy); Tue, 20 Jan 2026 19:47:35 -0500 X-ME-Sender: X-ME-Received: X-ME-Proxy-Cause: gggruggvucftvghtrhhoucdtuddrgeefgedrtddtgddugedukeelucetufdoteggodetrf dotffvucfrrhhofhhilhgvmecuhfgrshhtofgrihhlpdfurfetoffkrfgpnffqhgenuceu rghilhhouhhtmecufedttdenucesvcftvggtihhpihgvnhhtshculddquddttddmnecujf gurhepfffhvfevuffkfhggtggujgesthdtredttddtvdenucfhrhhomhepuehoqhhunhcu hfgvnhhguceosghoqhhunhdrfhgvnhhgsehgmhgrihhlrdgtohhmqeenucggtffrrghtth gvrhhnpeehudfgudffffetuedtvdehueevledvhfelleeivedtgeeuhfegueevieduffei vdenucevlhhushhtvghrufhiiigvpedtnecurfgrrhgrmhepmhgrihhlfhhrohhmpegsoh hquhhnodhmvghsmhhtphgruhhthhhpvghrshhonhgrlhhithihqdeiledvgeehtdeigedq udejjeekheehhedvqdgsohhquhhnrdhfvghngheppehgmhgrihhlrdgtohhmsehfihigmh gvrdhnrghmvgdpnhgspghrtghpthhtohepfedupdhmohguvgepshhmthhpohhuthdprhgt phhtthhopegrlhhitggvrhihhhhlsehgohhoghhlvgdrtghomhdprhgtphhtthhopeifih hllheskhgvrhhnvghlrdhorhhgpdhrtghpthhtohepphgvthgvrhiisehinhhfrhgruggv rggurdhorhhgpdhrtghpthhtoheprhhitghhrghrugdrhhgvnhguvghrshhonheslhhinh grrhhordhorhhgpdhrtghpthhtohepmhgrthhtshhtkeeksehgmhgrihhlrdgtohhmpdhr tghpthhtoheplhhinhhmrghgjeesghhmrghilhdrtghomhdprhgtphhtthhopegtrghtrg hlihhnrdhmrghrihhnrghssegrrhhmrdgtohhmpdhrtghpthhtohepohhjvggurgeskhgv rhhnvghlrdhorhhgpdhrtghpthhtohepghgrrhihsehgrghrhihguhhordhnvght X-ME-Proxy: Feedback-ID: iad51458e:Fastmail Received: by mail.messagingengine.com (Postfix) with ESMTPA; Tue, 20 Jan 2026 19:47:34 -0500 (EST) Date: Wed, 21 Jan 2026 08:47:32 +0800 From: Boqun Feng To: Alice Ryhl Cc: Will Deacon , Peter Zijlstra , Richard Henderson , Matt Turner , Magnus Lindholm , Catalin Marinas , Miguel Ojeda , Gary Guo , =?iso-8859-1?Q?Bj=F6rn?= Roy Baron , Benno Lossin , Andreas Hindborg , Trevor Gross , Danilo Krummrich , Mark Rutland , FUJITA Tomonori , Frederic Weisbecker , Lyude Paul , Thomas Gleixner , Anna-Maria Behnsen , John Stultz , Stephen Boyd , Alexander Viro , Christian Brauner , Jan Kara , linux-kernel@vger.kernel.org, linux-alpha@vger.kernel.org, linux-arm-kernel@lists.infradead.org, rust-for-linux@vger.kernel.org, linux-fsdevel@vger.kernel.org Subject: Re: [PATCH 5/5] rust: fs: use READ_ONCE instead of read_volatile Message-ID: References: <20251231-rwonce-v1-0-702a10b85278@google.com> <20251231-rwonce-v1-5-702a10b85278@google.com> Precedence: bulk X-Mailing-List: rust-for-linux@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20251231-rwonce-v1-5-702a10b85278@google.com> On Wed, Dec 31, 2025 at 12:22:29PM +0000, Alice Ryhl wrote: > Using `READ_ONCE` is the correct way to read the `f_flags` field. > > Signed-off-by: Alice Ryhl > --- > rust/kernel/fs/file.rs | 8 ++------ > 1 file changed, 2 insertions(+), 6 deletions(-) > > diff --git a/rust/kernel/fs/file.rs b/rust/kernel/fs/file.rs > index 23ee689bd2400565223181645157d832a836589f..6b07f08e7012f512e53743266096ce0076d29e1c 100644 > --- a/rust/kernel/fs/file.rs > +++ b/rust/kernel/fs/file.rs > @@ -335,12 +335,8 @@ pub fn cred(&self) -> &Credential { > /// The flags are a combination of the constants in [`flags`]. > #[inline] > pub fn flags(&self) -> u32 { > - // This `read_volatile` is intended to correspond to a READ_ONCE call. > - // > - // SAFETY: The file is valid because the shared reference guarantees a nonzero refcount. > - // > - // FIXME(read_once): Replace with `read_once` when available on the Rust side. > - unsafe { core::ptr::addr_of!((*self.as_ptr()).f_flags).read_volatile() } > + // SAFETY: The `f_flags` field of `struct file` is readable with `READ_ONCE`. > + unsafe { kernel::sync::READ_ONCE(&raw const (*self.as_ptr()).f_flags) } Not a question directly to this patch, but for FS folks: I see we read and write `f_flags` normally (i.e. without *_ONCE() or any atomic), and I don't see any synchronization between these read and write (maybe I'm missing something?), if read and write can happen at the same time, it's data race. So I assume we must have some assumption on the atomicity of these accesses to `f_flags`, could you may share or confirm this? Thanks Regards, Boqun > } > } > > > -- > 2.52.0.351.gbe84eed79e-goog >