From: Zhang Yi <yi.zhang@huaweicloud.com>
To: linux-xfs@vger.kernel.org, linux-fsdevel@vger.kernel.org
Cc: linux-kernel@vger.kernel.org, djwong@kernel.org,
hch@infradead.org, brauner@kernel.org, david@fromorbit.com,
chandanbabu@kernel.org, tytso@mit.edu, jack@suse.cz,
yi.zhang@huawei.com, yi.zhang@huaweicloud.com,
chengzhihao1@huawei.com, yukuai3@huawei.com
Subject: [PATCH v5 4/9] xfs: convert delayed extents to unwritten when zeroing post eof blocks
Date: Tue, 23 Apr 2024 19:17:35 +0800 [thread overview]
Message-ID: <20240423111735.1298851-1-yi.zhang@huaweicloud.com> (raw)
In-Reply-To: <20240320110548.2200662-5-yi.zhang@huaweicloud.com>
From: Zhang Yi <yi.zhang@huawei.com>
Current clone operation could be non-atomic if the destination of a file
is beyond EOF, user could get a file with corrupted (zeroed) data on
crash.
The problem is about preallocations. If you write some data into a file:
[A...B)
and XFS decides to preallocate some post-eof blocks, then it can create
a delayed allocation reservation:
[A.........D)
The writeback path tries to convert delayed extents to real ones by
allocating blocks. If there aren't enough contiguous free space, we can
end up with two extents, the first real and the second still delalloc:
[A....C)[C.D)
After that, both the in-memory and the on-disk file sizes are still B.
If we clone into the range [E...F) from another file:
[A....C)[C.D) [E...F)
then xfs_reflink_zero_posteof() calls iomap_zero_range() to zero out the
range [B, E) beyond EOF and flush it. Since [C, D) is still a delalloc
extent, its pagecache will be zeroed and both the in-memory and on-disk
size will be updated to D after flushing but before cloning. This is
wrong, because the user can see the size change and read the zeroes
while the clone operation is ongoing.
We need to keep the in-memory and on-disk size before the clone
operation starts, so instead of writing zeroes through the page cache
for delayed ranges beyond EOF, we convert these ranges to unwritten and
invalidate any cached data over that range beyond EOF.
Suggested-by: Dave Chinner <david@fromorbit.com>
Signed-off-by: Zhang Yi <yi.zhang@huawei.com>
---
Changes since v4:
Move the delalloc converting hunk before searching the COW fork. Because
if the file has been reflinked and copied on write,
xfs_bmap_extsize_align() aligned the range of COW delalloc extent, after
the writeback, there might be some unwritten extents left over in the
COW fork that overlaps the delalloc extent we found in data fork.
data fork ...wwww|dddddddddd...
cow fork |uuuuuuuuuu...
^
i_size
In my v4, we search the COW fork before checking the delalloc extent,
goto found_cow tag and return unconverted delalloc srcmap in the above
case, so the delayed extent in the data fork will have no chance to
convert to unwritten, it will lead to delalloc extent residue and break
generic/522 after merging patch 6.
fs/xfs/xfs_iomap.c | 28 ++++++++++++++++++++++++++++
1 file changed, 28 insertions(+)
diff --git a/fs/xfs/xfs_iomap.c b/fs/xfs/xfs_iomap.c
index 236ee78aa75b..ab398cb3680a 100644
--- a/fs/xfs/xfs_iomap.c
+++ b/fs/xfs/xfs_iomap.c
@@ -1022,6 +1022,23 @@ xfs_buffered_write_iomap_begin(
goto out_unlock;
}
+ /*
+ * For zeroing, trim a delalloc extent that extends beyond the EOF
+ * block. If it starts beyond the EOF block, convert it to an
+ * unwritten extent.
+ */
+ if ((flags & IOMAP_ZERO) && imap.br_startoff <= offset_fsb &&
+ isnullstartblock(imap.br_startblock)) {
+ xfs_fileoff_t eof_fsb = XFS_B_TO_FSB(mp, XFS_ISIZE(ip));
+
+ if (offset_fsb >= eof_fsb)
+ goto convert_delay;
+ if (end_fsb > eof_fsb) {
+ end_fsb = eof_fsb;
+ xfs_trim_extent(&imap, offset_fsb, end_fsb - offset_fsb);
+ }
+ }
+
/*
* Search the COW fork extent list even if we did not find a data fork
* extent. This serves two purposes: first this implements the
@@ -1167,6 +1184,17 @@ xfs_buffered_write_iomap_begin(
xfs_iunlock(ip, lockmode);
return xfs_bmbt_to_iomap(ip, iomap, &imap, flags, 0, seq);
+convert_delay:
+ xfs_iunlock(ip, lockmode);
+ truncate_pagecache(inode, offset);
+ error = xfs_bmapi_convert_delalloc(ip, XFS_DATA_FORK, offset,
+ iomap, NULL);
+ if (error)
+ return error;
+
+ trace_xfs_iomap_alloc(ip, offset, count, XFS_DATA_FORK, &imap);
+ return 0;
+
found_cow:
seq = xfs_iomap_inode_sequence(ip, 0);
if (imap.br_startoff <= offset_fsb) {
--
2.39.2
next prev parent reply other threads:[~2024-04-23 11:26 UTC|newest]
Thread overview: 30+ messages / expand[flat|nested] mbox.gz Atom feed top
2024-03-20 11:05 [PATCH v4 0/9] xfs/iomap: fix non-atomic clone operation and don't update size when zeroing range post eof Zhang Yi
2024-03-20 11:05 ` [PATCH v4 1/9] xfs: match lock mode in xfs_buffered_write_iomap_begin() Zhang Yi
2024-03-20 11:05 ` [PATCH v4 2/9] xfs: make the seq argument to xfs_bmapi_convert_delalloc() optional Zhang Yi
2024-03-20 11:05 ` [PATCH v4 3/9] xfs: make xfs_bmapi_convert_delalloc() to allocate the target offset Zhang Yi
2024-03-20 11:05 ` [PATCH v4 4/9] xfs: convert delayed extents to unwritten when zeroing post eof blocks Zhang Yi
2024-04-23 11:17 ` Zhang Yi [this message]
2024-04-25 12:22 ` [PATCH v5 " Christoph Hellwig
2024-04-25 12:32 ` Zhang Yi
2024-03-20 11:05 ` [PATCH v4 5/9] iomap: drop the write failure handles when unsharing and zeroing Zhang Yi
2024-03-20 11:05 ` [PATCH v4 6/9] iomap: don't increase i_size if it's not a write operation Zhang Yi
2024-04-19 6:07 ` Chandan Babu R
2024-04-19 8:14 ` Zhang Yi
2024-04-23 11:30 ` Zhang Yi
2024-03-20 11:05 ` [PATCH v4 7/9] iomap: use a new variable to handle the written bytes in iomap_write_iter() Zhang Yi
2024-03-20 11:05 ` [PATCH v4 8/9] iomap: make iomap_write_end() return a boolean Zhang Yi
2024-03-20 11:05 ` [PATCH v4 9/9] iomap: do some small logical cleanup in buffered write Zhang Yi
2024-04-17 4:42 ` [PATCH v4 0/9] xfs/iomap: fix non-atomic clone operation and don't update size when zeroing range post eof Chandan Babu R
2024-04-17 11:40 ` Christian Brauner
2024-04-18 9:30 ` Chandan Babu R
2024-04-25 12:25 ` (subset) " Christian Brauner
2024-04-29 11:48 ` Chandan Babu R
-- strict thread matches above, loose matches on Subject: below --
2024-04-25 13:13 [PATCH v5 " Zhang Yi
2024-04-25 13:13 ` [PATCH v5 4/9] xfs: convert delayed extents to unwritten when zeroing post eof blocks Zhang Yi
2024-04-25 18:29 ` Darrick J. Wong
2024-04-26 6:24 ` Zhang Yi
2024-04-26 6:33 ` Christoph Hellwig
2024-04-26 7:18 ` Zhang Yi
2024-04-27 6:59 ` Christoph Hellwig
2024-04-28 3:26 ` Zhang Yi
2024-04-29 4:41 ` Christoph Hellwig
2024-04-29 7:11 ` Zhang Yi
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=20240423111735.1298851-1-yi.zhang@huaweicloud.com \
--to=yi.zhang@huaweicloud.com \
--cc=brauner@kernel.org \
--cc=chandanbabu@kernel.org \
--cc=chengzhihao1@huawei.com \
--cc=david@fromorbit.com \
--cc=djwong@kernel.org \
--cc=hch@infradead.org \
--cc=jack@suse.cz \
--cc=linux-fsdevel@vger.kernel.org \
--cc=linux-kernel@vger.kernel.org \
--cc=linux-xfs@vger.kernel.org \
--cc=tytso@mit.edu \
--cc=yi.zhang@huawei.com \
--cc=yukuai3@huawei.com \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for read-only IMAP folder(s) and NNTP newsgroup(s).