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Message-ID: <87plokzuy6.ffs@tglx> Date: Mon, 30 Sep 2024 23:35:13 +0200 From: Thomas Gleixner <tglx@...utronix.de> To: Jeff Layton <jlayton@...nel.org>, John Stultz <jstultz@...gle.com>, Stephen Boyd <sboyd@...nel.org>, Alexander Viro <viro@...iv.linux.org.uk>, Christian Brauner <brauner@...nel.org>, Jan Kara <jack@...e.cz>, Steven Rostedt <rostedt@...dmis.org>, Masami Hiramatsu <mhiramat@...nel.org>, Mathieu Desnoyers <mathieu.desnoyers@...icios.com>, Jonathan Corbet <corbet@....net>, Chandan Babu R <chandan.babu@...cle.com>, "Darrick J. Wong" <djwong@...nel.org>, Theodore Ts'o <tytso@....edu>, Andreas Dilger <adilger.kernel@...ger.ca>, Chris Mason <clm@...com>, Josef Bacik <josef@...icpanda.com>, David Sterba <dsterba@...e.com>, Hugh Dickins <hughd@...gle.com>, Andrew Morton <akpm@...ux-foundation.org>, Chuck Lever <chuck.lever@...cle.com>, Vadim Fedorenko <vadim.fedorenko@...ux.dev> Cc: Randy Dunlap <rdunlap@...radead.org>, linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org, linux-trace-kernel@...r.kernel.org, linux-doc@...r.kernel.org, linux-xfs@...r.kernel.org, linux-ext4@...r.kernel.org, linux-btrfs@...r.kernel.org, linux-nfs@...r.kernel.org, linux-mm@...ck.org Subject: Re: [PATCH v8 01/11] timekeeping: move multigrain timestamp floor handling into timekeeper On Mon, Sep 30 2024 at 16:53, Jeff Layton wrote: > On Mon, 2024-09-30 at 22:19 +0200, Thomas Gleixner wrote: >> On Mon, Sep 30 2024 at 15:37, Jeff Layton wrote: >> > If however, two threads have racing syscalls that overlap in time, then there >> > is no such guarantee, and the second file may appear to have been modified >> > before, after or at the same time as the first, regardless of which one was >> > submitted first. >> >> 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? >> > > 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. The reason I'm asking is that if it's always syscall context, i.e. write() or io_uring()/RPC request etc., then you can avoid the whole global floor value dance and make it strictly per thread, which simplifies the exercise significantly. But even if it's not syscall/thread context then the worker or io_uring state machine might just require to serialize against itself and not coordinate with something else. But what do I know. Thanks, tglx
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