From: Al Viro <viro@zeniv.linux.org.uk>
To: Joshua Hudson <joshudson@gmail.com>
Cc: Bagas Sanjaya <bagasdotme@gmail.com>,
Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
Linux IDE and libata <linux-ide@vger.kernel.org>,
Hans de Goede <hdegoede@redhat.com>, Jens Axboe <axboe@kernel.dk>,
Damien Le Moal <dlemoal@kernel.org>,
OGAWA Hirofumi <hirofumi@mail.parknet.co.jp>
Subject: Re: Cache coherency bug: stale reads on /dev/sda1
Date: Sun, 27 Aug 2023 03:06:35 +0100 [thread overview]
Message-ID: <20230827020635.GQ3390869@ZenIV> (raw)
In-Reply-To: <CA+jjjYT6+NJwB2Kn0jWLKtmz3dWH6UnVJNA6vDbPXnnJnHMf9Q@mail.gmail.com>
On Sat, Aug 26, 2023 at 06:25:58PM -0700, Joshua Hudson wrote:
> I am presuming you mean "Are you sure this not a hardware issue?"
>
> I am sure it is not, for two reasons.
>
> 1) If it were a hardware issue I would still expect the two device
> nodes (whole disk and partition) to report the *same* data.
>
> 2) I have since developed a workaround involving BLKFLSDEV. The
> workaround is really ugly.
Whole disk and all partitions have page caches of their own.
There is no coherency between those; write through one, then
read through another and you are not guaranteed that read won't
see the stale cached data.
Doctor, it hurts when I do it...
Incidentally, read from device/write to the place you've read via
file/read from device again also has no coherency warranties, for
exact same reason.
IOW, not a bug.
next prev parent reply other threads:[~2023-08-27 2:07 UTC|newest]
Thread overview: 11+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-08-26 21:59 Cache coherency bug: stale reads on /dev/sda1 Joshua Hudson
2023-08-27 1:03 ` Bagas Sanjaya
2023-08-27 1:25 ` Joshua Hudson
2023-08-27 2:06 ` Al Viro [this message]
2023-08-27 2:38 ` Joshua Hudson
2023-08-27 2:50 ` Bagas Sanjaya
2023-08-27 4:17 ` Al Viro
2023-08-27 14:39 ` Joshua Hudson
2023-08-27 16:30 ` Al Viro
2023-08-27 18:33 ` Joshua Hudson
2023-09-06 7:42 ` Hannes Reinecke
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