linux-kernel - Re: [RFC] metadata updates vs. fetches (was Re: [PATCH v4] fs: Fix data race in inode_set_ctime_to

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Message-ID: <Z0PPl_B6kxGRCZk7@casper.infradead.org>
Date: Mon, 25 Nov 2024 01:15:03 +0000
From: Matthew Wilcox <willy@...radead.org>
To: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: Al Viro <viro@...iv.linux.org.uk>, Mateusz Guzik <mjguzik@...il.com>,
	"Darrick J. Wong" <djwong@...nel.org>,
	Hao-ran Zheng <zhenghaoran@...a.edu.cn>, brauner@...nel.org,
	jack@...e.cz, linux-fsdevel@...r.kernel.org,
	linux-kernel@...r.kernel.org, baijiaju1990@...il.com,
	21371365@...a.edu.cn
Subject: Re: [RFC] metadata updates vs. fetches (was Re: [PATCH v4] fs: Fix
 data race in inode_set_ctime_to_ts)

On Sun, Nov 24, 2024 at 04:53:39PM -0800, Linus Torvalds wrote:
> On Sun, 24 Nov 2024 at 15:53, Matthew Wilcox <willy@...radead.org> wrote:
> Look, let's write 5.000950, 6.000150 and 7.000950, while there is a
> single reader (and let's assume these are all properly ordered reads
> and writes):
> 
>   W1.s 5
>   W1.ns 950
>   W2.s 6
>   R.ns (950)
>   R.s (6)
>   W2.ns 150
>   W3.s 7
>   W3.ns 950
>   R.ns (950)
> 
> and look how the reader is happy, because it got the same nanoseconds
> twice. But the reader thinks it had a time of 6.000950, and AT NO
> POINT was that actually a valid time.

I literally said that.

"Now we have a time of 6:950 which is never a time that this file had,
but it's intermediate in time between two times that the file _did_
have, so it won't break make."