From: Christoph Hellwig <hch@infradead.org>
To: Jan Kara <jack@suse.cz>
Cc: Christoph Hellwig <hch@infradead.org>, Qu Wenruo <wqu@suse.com>,
linux-btrfs@vger.kernel.org, djwong@kernel.org,
linux-xfs@vger.kernel.org, linux-fsdevel@vger.kernel.org,
linux-block@vger.kernel.org, linux-mm@kvack.org,
martin.petersen@oracle.com, jack@suse.com
Subject: Re: O_DIRECT vs BLK_FEAT_STABLE_WRITES, was Re: [PATCH] btrfs: never trust the bio from direct IO
Date: Mon, 20 Oct 2025 04:44:27 -0700 [thread overview]
Message-ID: <aPYgm3ey4eiFB4_o@infradead.org> (raw)
In-Reply-To: <56o3re2wspflt32t6mrfg66dec4hneuixheroax2lmo2ilcgay@zehhm5yaupav>
On Mon, Oct 20, 2025 at 01:16:39PM +0200, Jan Kara wrote:
> Hmm, this is an interesting twist in the problems with pinned pages - so
> far I was thinking about problems where pinned page cache page gets
> modified (e.g. through DIO or RDMA) and this causes checksum failures if
> it races with writeback. If I understand you right, now you are concerned
> about a situation where some page is used as a buffer for direct IO write
> / RDMA and it gets modified while the DMA is running which causes checksum
> mismatch?
Really all of the above. Even worse this can also happen for reads,
e.g. when the parity or checksum is calculated in the user buffer.
> Writeprotecting the buffer before the DIO starts isn't that hard
> to do (although it has a non-trivial cost) but we don't have a mechanism to
> make sure the page cannot be writeably mapped while it is pinned (and
> avoiding that without introducing deadlocks would be *fun*).
Well, this goes back to the old idea of maybe bounce buffering in that
case?
next prev parent reply other threads:[~2025-10-20 11:44 UTC|newest]
Thread overview: 28+ messages / expand[flat|nested] mbox.gz Atom feed top
2025-10-20 9:19 [PATCH] btrfs: never trust the bio from direct IO Qu Wenruo
2025-10-20 10:00 ` O_DIRECT vs BLK_FEAT_STABLE_WRITES, was " Christoph Hellwig
2025-10-20 10:24 ` Qu Wenruo
2025-10-20 11:45 ` Christoph Hellwig
2025-10-20 11:16 ` Jan Kara
2025-10-20 11:44 ` Christoph Hellwig [this message]
2025-10-20 13:59 ` Jan Kara
2025-10-20 14:59 ` Matthew Wilcox
2025-10-20 15:58 ` Jan Kara
2025-10-20 17:55 ` John Hubbard
2025-10-21 8:27 ` Jan Kara
2025-10-21 16:56 ` John Hubbard
2025-10-20 19:00 ` David Hildenbrand
2025-10-21 7:49 ` Christoph Hellwig
2025-10-21 7:57 ` David Hildenbrand
2025-10-21 9:33 ` Jan Kara
2025-10-21 9:43 ` David Hildenbrand
2025-10-21 9:22 ` Jan Kara
2025-10-21 9:37 ` David Hildenbrand
2025-10-21 9:52 ` Jan Kara
2025-10-21 3:17 ` Qu Wenruo
2025-10-21 7:48 ` Christoph Hellwig
2025-10-21 8:15 ` Qu Wenruo
2025-10-21 11:30 ` Johannes Thumshirn
2025-10-22 2:27 ` Qu Wenruo
2025-10-22 5:04 ` hch
2025-10-22 6:17 ` Qu Wenruo
2025-10-22 6:24 ` hch
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