From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 46D95174EF0; Mon, 30 Sep 2024 20:53:07 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1727729588; cv=none; b=p0EsnO6VMSXEwl//ZnudapDYM6viKtdPYlhgG4RlUCI3J+WFIq4hFJwxgmUnXieU90eRDoMDnZiVOzSv2G4WYsijIatMQlCXCsWzQgnDe9spsxLVVY4H4/Rw0eDQ5y70e2SNMso2LEUlz88nDDmiLQczCOXUiE6gCnc8b3unZMo= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1727729588; c=relaxed/simple; bh=vlbOwfejgzFyaPx+89o1KS6bbtm/N5DTnVSx2O4DToM=; h=Message-ID:Subject:From:To:Cc:Date:In-Reply-To:References: Content-Type:MIME-Version; b=DvbbLfFFjw16ntlfRpB4zi36Z7ANvs8DIg5DQAOHhMnMJSy5UBQWJG8kfYwoTqzYQL/06EWVWnA1O06urelYyIp1nBoStfMMyL6a95hTplpOMaRJUelEU8r6UkrV7fvRwEj1b8r4g5pzu4GLa3EhaG9QrDTYKYp72UVPCorx1mA= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=pbWigjOl; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="pbWigjOl" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 5D64BC4CEC7; Mon, 30 Sep 2024 20:53:05 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1727729587; bh=vlbOwfejgzFyaPx+89o1KS6bbtm/N5DTnVSx2O4DToM=; h=Subject:From:To:Cc:Date:In-Reply-To:References:From; b=pbWigjOlhOy/R7X2peSZZsa09l/9riJ7oXPC7ttPSebGdV0/tdn6b6UTxvoYgR5NH SwkvYZVm6yvR5woy59UJ5u06uaKrM7oUVgTp3yhTHEV9U+942t3v90zOYjMgl2ittz 6atbWTVO6oAjkM6KPYbz4p88SYg/Ap/Hbsm3CZBU9tILdBIeVdZhjZ9mV9cE51rW8y s92tFtqYV29HblqnxCP862JmzEHmS3x+MXj4nylSJKTnaZEOXtyZ6irzz6p1hUOK9e hCK8HyfqqhUrBLbXXqZUTChFM3UXfuiukl3uX5Fjul24tnDcfglbR0PSIoLcpV4lpP TqAVyeOnX4QwQ== Message-ID: <79a32ab9308d6e63e066aa17c5c2492b51b55850.camel@kernel.org> Subject: Re: [PATCH v8 01/11] timekeeping: move multigrain timestamp floor handling into timekeeper From: Jeff Layton To: Thomas Gleixner , John Stultz , Stephen Boyd , Alexander Viro , Christian Brauner , Jan Kara , Steven Rostedt , Masami Hiramatsu , Mathieu Desnoyers , Jonathan Corbet , Chandan Babu R , "Darrick J. Wong" , Theodore Ts'o , Andreas Dilger , Chris Mason , Josef Bacik , David Sterba , Hugh Dickins , Andrew Morton , Chuck Lever , Vadim Fedorenko Cc: Randy Dunlap , linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-trace-kernel@vger.kernel.org, linux-doc@vger.kernel.org, linux-xfs@vger.kernel.org, linux-ext4@vger.kernel.org, linux-btrfs@vger.kernel.org, linux-nfs@vger.kernel.org, linux-mm@kvack.org Date: Mon, 30 Sep 2024 16:53:04 -0400 In-Reply-To: <87y138zyfu.ffs@tglx> References: <20240914-mgtime-v8-0-5bd872330bed@kernel.org> <20240914-mgtime-v8-1-5bd872330bed@kernel.org> <87a5g79aag.ffs@tglx> <874j6f99dg.ffs@tglx> <878qv90x6w.ffs@tglx> <4933075b1023f466edb516e86608e0938de28c1d.camel@kernel.org> <87y138zyfu.ffs@tglx> Autocrypt: addr=jlayton@kernel.org; prefer-encrypt=mutual; keydata=mQINBE6V0TwBEADXhJg7s8wFDwBMEvn0qyhAnzFLTOCHooMZyx7XO7dAiIhDSi7G1NPxw n8jdFUQMCR/GlpozMFlSFiZXiObE7sef9rTtM68ukUyZM4pJ9l0KjQNgDJ6Fr342Htkjxu/kFV1Wv 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linux-fsdevel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 On Mon, 2024-09-30 at 22:19 +0200, Thomas Gleixner wrote: > On Mon, Sep 30 2024 at 15:37, Jeff Layton wrote: > > On Mon, 2024-09-30 at 21:16 +0200, Thomas Gleixner wrote: > > I have the following section in the multigrain-ts.rst file that gets > > added in patch 7 of this series. I'll also plan to add some extra > > wording about how backward realtime clock jumps can affect ordering: >=20 > Please also add comments into the code / interface. >=20 Will do. > > Inode Timestamp Ordering > > =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D= =3D > >=20 > > In addition to providing info about changes to individual files, file = =20 > > timestamps also serve an important purpose in applications like "make".= These =20 > > programs measure timestamps in order to determine whether source files = might be =20 > > newer than cached objects. = =20 > >=20 > > Userland applications like make can only determine ordering based on = =20 > > operational boundaries. For a syscall those are the syscall entry and e= xit =20 > > points. For io_uring or nfsd operations, that's the request submission = and =20 > > response. In the case of concurrent operations, userland can make no = =20 > > determination about the order in which things will occur. > >=20 > > For instance, if a single thread modifies one file, and then another fi= le in =20 > > sequence, the second file must show an equal or later mtime than the fi= rst. The =20 > > same is true if two threads are issuing similar operations that do not = overlap =20 > > in time. > >=20 > > If however, two threads have racing syscalls that overlap in time, then= there =20 > > is no such guarantee, and the second file may appear to have been modif= ied =20 > > before, after or at the same time as the first, regardless of which one= was =20 > > submitted first. >=20 > That makes me ask a question. Are the timestamps always taken in thread > (syscall) context or can they be taken in other contexts (worker, > [soft]interrupt, etc.) too? >=20 That's a good question. The main place we do this is inode_set_ctime_current(). That is mostly called in the context of a syscall or similar sort of operation (io_uring, nfsd RPC request, etc.). I certainly wouldn't rule out a workqueue job calling that function, but this is something we do while dirtying an inode, and that's not typically done in interrupt context. --=20 Jeff Layton