From: John Garry <john.g.garry@oracle.com>
To: Dave Chinner <david@fromorbit.com>
Cc: djwong@kernel.org, hch@lst.de, viro@zeniv.linux.org.uk,
brauner@kernel.org, jack@suse.cz, chandan.babu@oracle.com,
willy@infradead.org, axboe@kernel.dk, martin.petersen@oracle.com,
linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org,
tytso@mit.edu, jbongio@google.com, ojaswin@linux.ibm.com,
ritesh.list@gmail.com, mcgrof@kernel.org, p.raghav@samsung.com,
linux-xfs@vger.kernel.org, catherine.hoang@oracle.com
Subject: Re: [PATCH v3 17/21] iomap: Atomic write support
Date: Thu, 2 May 2024 10:12:36 +0100 [thread overview]
Message-ID: <70bc1a7f-1218-46d6-a8e8-96b667d393b7@oracle.com> (raw)
In-Reply-To: <ZjLvw3Y5m9AxH71u@dread.disaster.area>
On 02/05/2024 02:43, Dave Chinner wrote:
> On Wed, May 01, 2024 at 12:08:34PM +0100, John Garry wrote:
>> On 01/05/2024 02:47, Dave Chinner wrote:
>>> On Mon, Apr 29, 2024 at 05:47:42PM +0000, John Garry wrote:
>>>> Support atomic writes by producing a single BIO with REQ_ATOMIC flag set.
>>>>
>>>> We rely on the FS to guarantee extent alignment, such that an atomic write
>>>> should never straddle two or more extents. The FS should also check for
>>>> validity of an atomic write length/alignment.
>>>>
>>>> Signed-off-by: John Garry <john.g.garry@oracle.com>
>>>> ---
> ...
>>>> +
>>>> bio->bi_private = dio;
>>>> bio->bi_end_io = iomap_dio_bio_end_io;
>>>> @@ -403,6 +407,12 @@ static loff_t iomap_dio_bio_iter(const struct iomap_iter *iter,
>>>> }
>>>> n = bio->bi_iter.bi_size;
>>>> + if (is_atomic && n != orig_count) {
>>>> + /* This bio should have covered the complete length */
>>>> + ret = -EINVAL;
>>>> + bio_put(bio);
>>>> + goto out;
>>>> + }
>>>
>>> What happens now if we've done zeroing IO before this? I suspect we
>>> might expose stale data if the partial block zeroing converts the
>>> unwritten extent in full...
>>
>> We use iomap_dio.ref to ensure that __iomap_dio_rw() does not return until
>> any zeroing and actual sub-io block write completes. See iomap_dio_zero() ->
>> iomap_dio_submit_bio() -> atomic_inc(&dio->ref) callchain. I meant to add
>> such info to the commit message, as you questioned this previously.
>
> Yes, I get that. But my point is that we may have only done -part-
> of a block unaligned IO.
>
> This is effectively a failure from a bio_iov_iter_get_pages() call.
> What does the bio_iov_iter_get_pages() failure case do that this new
> failure case not do? Why does this case have different failure
> handling?
>
So you are saying that if we fail here (that is the (is_atomic && n !=
orig_count) check), anything unwritten in the atomic write region and
zerotail region could expose stale data, right?
If so, I would say that we need to zero the complete unwritten atomic
write and zerotail regions - similar to the bio_iov_iter_get_pages()
failure handling - and still report an -EINVAL error.
How does that sound?
Thanks,
John
next prev parent reply other threads:[~2024-05-02 9:13 UTC|newest]
Thread overview: 49+ messages / expand[flat|nested] mbox.gz Atom feed top
2024-04-29 17:47 [PATCH v3 00/21] block atomic writes for XFS John Garry
2024-04-29 17:47 ` [PATCH v3 01/21] fs: Add generic_atomic_write_valid_size() John Garry
2024-04-29 17:47 ` [PATCH v3 02/21] xfs: only allow minlen allocations when near ENOSPC John Garry
2024-04-29 17:47 ` [PATCH v3 03/21] xfs: always tail align maxlen allocations John Garry
2024-04-29 17:47 ` [PATCH v3 04/21] xfs: simplify extent allocation alignment John Garry
2024-04-29 17:47 ` [PATCH v3 05/21] xfs: make EOF allocation simpler John Garry
2024-04-29 17:47 ` [PATCH v3 06/21] xfs: introduce forced allocation alignment John Garry
2024-04-29 17:47 ` [PATCH v3 07/21] fs: xfs: align args->minlen for " John Garry
2024-04-29 17:47 ` [PATCH v3 08/21] xfs: Introduce FORCEALIGN inode flag John Garry
2024-04-30 23:22 ` Dave Chinner
2024-05-01 10:03 ` John Garry
2024-05-02 0:50 ` Dave Chinner
2024-05-02 7:56 ` John Garry
2024-04-29 17:47 ` [PATCH v3 09/21] xfs: Do not free EOF blocks for forcealign John Garry
2024-04-30 22:54 ` Dave Chinner
2024-05-01 8:30 ` John Garry
2024-05-02 1:11 ` Dave Chinner
2024-05-02 8:55 ` John Garry
2024-04-29 17:47 ` [PATCH v3 10/21] xfs: Update xfs_is_falloc_aligned() mask " John Garry
2024-04-30 23:35 ` Dave Chinner
2024-05-01 10:48 ` John Garry
2024-05-01 23:45 ` Darrick J. Wong
2024-04-29 17:47 ` [PATCH RFC v3 11/21] xfs: Unmap blocks according to forcealign John Garry
2024-05-01 0:10 ` Dave Chinner
2024-05-01 10:54 ` John Garry
2024-04-29 17:47 ` [PATCH RFC v3 12/21] xfs: Only free full extents for forcealign John Garry
2024-05-01 0:53 ` Dave Chinner
2024-05-01 11:24 ` John Garry
2024-05-01 23:53 ` Darrick J. Wong
2024-05-02 3:12 ` Dave Chinner
2024-04-29 17:47 ` [PATCH v3 13/21] xfs: Enable file data forcealign feature John Garry
2024-04-29 17:47 ` [PATCH v3 14/21] iomap: Sub-extent zeroing John Garry
2024-05-01 1:07 ` Dave Chinner
2024-05-01 10:23 ` John Garry
2024-05-30 10:40 ` John Garry
2024-04-29 17:47 ` [PATCH v3 15/21] fs: xfs: " John Garry
2024-05-01 1:32 ` Dave Chinner
2024-05-01 11:36 ` John Garry
2024-05-02 1:26 ` Dave Chinner
2024-04-29 17:47 ` [PATCH v3 16/21] fs: Add FS_XFLAG_ATOMICWRITES flag John Garry
2024-04-29 17:47 ` [PATCH v3 17/21] iomap: Atomic write support John Garry
2024-05-01 1:47 ` Dave Chinner
2024-05-01 11:08 ` John Garry
2024-05-02 1:43 ` Dave Chinner
2024-05-02 9:12 ` John Garry [this message]
2024-04-29 17:47 ` [PATCH v3 18/21] xfs: Support FS_XFLAG_ATOMICWRITES for forcealign John Garry
2024-04-29 17:47 ` [PATCH v3 19/21] xfs: Support atomic write for statx John Garry
2024-04-29 17:47 ` [PATCH v3 20/21] xfs: Validate atomic writes John Garry
2024-04-29 17:47 ` [PATCH v3 21/21] xfs: Support setting FMODE_CAN_ATOMIC_WRITE John Garry
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