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

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Message-ID: <e644366b-8387-c228-78cb-f108453b0b1d@gmail.com>
Date:   Sun, 27 Aug 2023 09:50:46 +0700
From:   Bagas Sanjaya <bagasdotme@...il.com>
To:     Joshua Hudson <joshudson@...il.com>,
        Al Viro <viro@...iv.linux.org.uk>
Cc:     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 27/08/2023 09:38, 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.
> 
> There's also the astounding: write stuff to disk, umount everything,
> copy one disk to
> another using the whole disk device doesn't work because reading the whole disk
> yields a stale cache (sometimes).
> 
> On the other hand, I can think of very few cases where the file vs
> disk buffer pool
> matters, because the loop device is unaffected (writing to a loop
> block device is
> coherent with the file).
> 

tl;dr:

> A: http://en.wikipedia.org/wiki/Top_post
> Q: Were do I find info about this thing called top-posting?
> A: Because it messes up the order in which people normally read text.
> Q: Why is top-posting such a bad thing?
> A: Top-posting.
> Q: What is the most annoying thing in e-mail?
> 
> A: No.
> Q: Should I include quotations after my reply?
> 
> http://daringfireball.net/2007/07/on_top

What cases on the loop devices?

-- 
An old man doll... just what I always wanted! - Clara