From: Ming Lei <ming.lei@redhat.com>
To: hch <hch@lst.de>
Cc: Johannes Thumshirn <Johannes.Thumshirn@wdc.com>,
"Darrick J. Wong" <djwong@kernel.org>, Jan Kara <jack@suse.cz>,
Keith Busch <kbusch@kernel.org>,
Dave Chinner <david@fromorbit.com>,
Carlos Maiolino <cem@kernel.org>,
Christian Brauner <brauner@kernel.org>,
"Martin K. Petersen" <martin.petersen@oracle.com>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
"linux-xfs@vger.kernel.org" <linux-xfs@vger.kernel.org>,
"linux-fsdevel@vger.kernel.org" <linux-fsdevel@vger.kernel.org>,
"linux-raid@vger.kernel.org" <linux-raid@vger.kernel.org>,
"linux-block@vger.kernel.org" <linux-block@vger.kernel.org>
Subject: Re: fall back from direct to buffered I/O when stable writes are required
Date: Wed, 12 Nov 2025 22:18:40 +0800 [thread overview]
Message-ID: <aRSXQKgkV55fFtNG@fedora> (raw)
In-Reply-To: <20251106124900.GA6144@lst.de>
On Thu, Nov 06, 2025 at 01:49:00PM +0100, hch wrote:
> On Thu, Nov 06, 2025 at 09:50:10AM +0000, Johannes Thumshirn wrote:
> > On 11/5/25 10:44 PM, Darrick J. Wong wrote:
> > > Just out of curiosity -- is qemu itself mutating the buffers that it is
> > > passing down to the lower levels via dio? Or is it a program in the
> > > guest that's mutating buffers that are submitted for dio, which then get
> > > zerocopied all the way down to the hypervisor?
> >
> > If my memory serves me right it is the guest (or at least can be). I
> > remember a bug report on btrfs where a Windows guest had messed up
> > checksums because of modifying inflight I/O.
>
> qemu passes I/O through, so yes it is guest controller. Windows is most
> famous, but the Linux swap code can trigger it easily too.
Looks buffer overwrite is actually done by buggy software in guest side,
why is qemu's trouble? Or will qemu IO emulator write to the IO buffer
when guest IO is inflight?
Thanks,
Ming
next prev parent reply other threads:[~2025-11-12 14:19 UTC|newest]
Thread overview: 61+ messages / expand[flat|nested] mbox.gz Atom feed top
2025-10-29 7:15 fall back from direct to buffered I/O when stable writes are required Christoph Hellwig
2025-10-29 7:15 ` [PATCH 1/4] fs: replace FOP_DIO_PARALLEL_WRITE with a fmode bits Christoph Hellwig
2025-10-29 16:01 ` Darrick J. Wong
2025-11-04 7:00 ` Nirjhar Roy (IBM)
2025-11-05 14:04 ` Christoph Hellwig
2025-11-11 9:44 ` Christian Brauner
2025-10-29 7:15 ` [PATCH 2/4] fs: return writeback errors for IOCB_DONTCACHE in generic_write_sync Christoph Hellwig
2025-10-29 16:01 ` Darrick J. Wong
2025-10-29 16:37 ` Christoph Hellwig
2025-10-29 18:12 ` Darrick J. Wong
2025-10-30 5:59 ` Christoph Hellwig
2025-11-04 12:04 ` Nirjhar Roy (IBM)
2025-11-04 15:53 ` Christoph Hellwig
2025-10-29 7:15 ` [PATCH 3/4] xfs: use IOCB_DONTCACHE when falling back to buffered writes Christoph Hellwig
2025-10-29 15:57 ` Darrick J. Wong
2025-11-04 12:33 ` Nirjhar Roy (IBM)
2025-11-04 15:52 ` Christoph Hellwig
2025-10-29 7:15 ` [PATCH 4/4] xfs: fallback to buffered I/O for direct I/O when stable writes are required Christoph Hellwig
2025-10-29 15:53 ` Darrick J. Wong
2025-10-29 16:35 ` Christoph Hellwig
2025-10-29 21:23 ` Qu Wenruo
2025-10-30 5:58 ` Christoph Hellwig
2025-10-30 6:37 ` Qu Wenruo
2025-10-30 6:49 ` Christoph Hellwig
2025-10-30 6:53 ` Qu Wenruo
2025-10-30 6:55 ` Christoph Hellwig
2025-10-30 7:14 ` Qu Wenruo
2025-10-30 7:17 ` Christoph Hellwig
2025-11-10 13:38 ` Nirjhar Roy (IBM)
2025-11-10 13:59 ` Christoph Hellwig
2025-11-12 7:13 ` Nirjhar Roy (IBM)
2025-10-29 15:58 ` fall back from direct to buffered " Bart Van Assche
2025-10-29 16:14 ` Darrick J. Wong
2025-10-29 16:33 ` Christoph Hellwig
2025-10-30 11:20 ` Dave Chinner
2025-10-30 12:00 ` Geoff Back
2025-10-30 12:54 ` Jan Kara
2025-10-30 14:35 ` Christoph Hellwig
2025-10-30 22:02 ` Dave Chinner
2025-10-30 14:33 ` Christoph Hellwig
2025-10-30 23:18 ` Dave Chinner
2025-10-31 13:00 ` Christoph Hellwig
2025-10-31 15:57 ` Keith Busch
2025-10-31 16:47 ` Christoph Hellwig
2025-11-03 11:14 ` Jan Kara
2025-11-03 12:21 ` Christoph Hellwig
2025-11-03 22:47 ` Keith Busch
2025-11-04 23:38 ` Darrick J. Wong
2025-11-05 14:11 ` Christoph Hellwig
2025-11-05 21:44 ` Darrick J. Wong
2025-11-06 9:50 ` Johannes Thumshirn
2025-11-06 12:49 ` hch
2025-11-12 14:18 ` Ming Lei [this message]
2025-11-12 14:38 ` hch
2025-11-13 17:39 ` Kevin Wolf
2025-11-14 5:39 ` Christoph Hellwig
2025-11-14 9:29 ` Kevin Wolf
2025-11-14 12:01 ` Christoph Hellwig
2025-11-14 12:31 ` Kevin Wolf
2025-11-14 15:36 ` Christoph Hellwig
2025-11-14 16:55 ` Kevin Wolf
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