linux-kernel - Re: Cache coherency bug: stale reads on /dev/sda1

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Message-ID: <20230827041716.GR3390869@ZenIV>
Date:   Sun, 27 Aug 2023 05:17:16 +0100
From:   Al Viro <viro@...iv.linux.org.uk>
To:     Joshua Hudson <joshudson@...il.com>
Cc:     Bagas Sanjaya <bagasdotme@...il.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Linux IDE and libata <linux-ide@...r.kernel.org>,
        Hans de Goede <hdegoede@...hat.com>,
        Jens Axboe <axboe@...nel.dk>,
        Damien Le Moal <dlemoal@...nel.org>,
        OGAWA Hirofumi <hirofumi@...l.parknet.co.jp>
Subject: Re: Cache coherency bug: stale reads on /dev/sda1

On Sat, Aug 26, 2023 at 07:38:57PM -0700, Joshua Hudson wrote:
> "Whole disk and all partitions have page caches of their own."
> 
> That's so bad.
> 
> I can think of numerous cases where this will cause problems; including
> some I encountered last year and did not understand at the time. Manipulating
> EFI partitions through the whole disk device makes sense because FAT filesystems
> *know their offset on the disk*, and some of the existing tools really
> don't like being
> given a partition device.

Explain, please.  How does FAT filesystem know its offset on disk?
Since when?  It had always been possible to copy a FAT image into
a partition verbatim and it works no matter where on disk that
partition happens to be...

Has that changed at some point?  Do you have any references?  Ideally
with some kind of rationale for that weirdness...

Or am I misparsing what you wrote?