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From: Junxiao Bi <junxiao.bi@oracle.com>
To: ocfs2-devel@oss.oracle.com
Subject: [Ocfs2-devel] [PATCH 2/2] ocfs2: issue zeroout to EOF blocks
Date: Tue, 13 Jul 2021 14:13:06 -0700	[thread overview]
Message-ID: <20210713211306.50593-2-junxiao.bi@oracle.com> (raw)
In-Reply-To: <20210713211306.50593-1-junxiao.bi@oracle.com>

For punch holes in EOF blocks, fallocate used buffer write to zero
the EOF blocks in last cluster. But since ->writepage will ignore
EOF pages, those zeros will not be flushed. This "looks" ok as
commit 6bba4471f0cc ("ocfs2: fix data corruption by fallocate")
will zero the EOF blocks when extend the file size, but it isn't.
The problem happened on those EOF pages, before writeback, those
pages had DIRTY flag set and all buffer_head in them also had
DIRTY flag set, when writeback run by write_cache_pages(), DIRTY
flag on the page was cleared, but DIRTY flag on the buffer_head
not. When next write happened to those EOF pages, since buffer_head
already had DIRTY flag set, it would not mark page DIRTY again.
That made writeback ignore them forever. That will cause data
corruption. Even directio write can't work because it will fail
when trying to drop pages caches before direct io, as it found
the buffer_head for those pages still had DIRTY flag set, then
it will fall back to buffer io mode.
To make a summary of the issue, as writeback ingores EOF pages,
once any EOF page is generated, any write to it will only go
to the page cache, it will never be flushed to disk even file
size extends and that page is not EOF page any more.
The fix is to avoid zero EOF blocks with buffer write.

The following code snippet from qemu-img could trigger the corruption.

656   open("6b3711ae-3306-4bdd-823c-cf1c0060a095.conv.2", O_RDWR|O_DIRECT|O_CLOEXEC) = 11
...
660   fallocate(11, FALLOC_FL_KEEP_SIZE|FALLOC_FL_PUNCH_HOLE, 2275868672, 327680 <unfinished ...>
660   fallocate(11, 0, 2275868672, 327680) = 0
658   pwrite64(11, "\0\31\237\v\0\336\330\f\0\373~\r\0\300\270\16\0\335^\17\0\242\230\20\0\277>\21\0\204x\22"..., 311296, 2275868672) = 311296

Cc: <stable@vger.kernel.org>
Signed-off-by: Junxiao Bi <junxiao.bi@oracle.com>
---
 fs/ocfs2/file.c | 99 ++++++++++++++++++++++++++++++-------------------
 1 file changed, 60 insertions(+), 39 deletions(-)

diff --git a/fs/ocfs2/file.c b/fs/ocfs2/file.c
index 53bb46ce3cbb..984b950f5abc 100644
--- a/fs/ocfs2/file.c
+++ b/fs/ocfs2/file.c
@@ -1529,6 +1529,45 @@ static void ocfs2_truncate_cluster_pages(struct inode *inode, u64 byte_start,
 	}
 }
 
+/*
+ * zero out partial blocks of one cluster.
+ *
+ * start: file offset where zero starts, will be made upper block aligned.
+ * len: it will be trimmed to the end of current cluster if "start + len"
+ *      is bigger than it.
+ */
+static int ocfs2_zeroout_partial_cluster(struct inode *inode,
+					u64 start, u64 len)
+{
+	int ret;
+	u64 start_block, end_block, nr_blocks;
+	u64 p_block, offset;
+	u32 cluster, p_cluster, nr_clusters;
+	struct super_block *sb = inode->i_sb;
+	u64 end = ocfs2_align_bytes_to_clusters(sb, start);
+
+	if (start + len < end)
+		end = start + len;
+
+	start_block = ocfs2_blocks_for_bytes(sb, start);
+	end_block = ocfs2_blocks_for_bytes(sb, end);
+	nr_blocks = end_block - start_block;
+	if (!nr_blocks)
+		return 0;
+
+	cluster = ocfs2_bytes_to_clusters(sb, start);
+	ret = ocfs2_get_clusters(inode, cluster, &p_cluster,
+				&nr_clusters, NULL);
+	if (ret)
+		return ret;
+	if (!p_cluster)
+		return 0;
+
+	offset = start_block - ocfs2_clusters_to_blocks(sb, cluster);
+	p_block = ocfs2_clusters_to_blocks(sb, p_cluster) + offset;
+	return sb_issue_zeroout(sb, p_block, nr_blocks, GFP_NOFS);
+}
+
 static int ocfs2_zero_partial_clusters(struct inode *inode,
 				       u64 start, u64 len)
 {
@@ -1538,6 +1577,7 @@ static int ocfs2_zero_partial_clusters(struct inode *inode,
 	struct ocfs2_super *osb = OCFS2_SB(inode->i_sb);
 	unsigned int csize = osb->s_clustersize;
 	handle_t *handle;
+	loff_t isize = i_size_read(inode);
 
 	/*
 	 * The "start" and "end" values are NOT necessarily part of
@@ -1558,6 +1598,26 @@ static int ocfs2_zero_partial_clusters(struct inode *inode,
 	if ((start & (csize - 1)) == 0 && (end & (csize - 1)) == 0)
 		goto out;
 
+	/* No page cache for EOF blocks, issue zero out to disk. */
+	if (end > isize) {
+		/*
+		 * zeroout eof blocks in last cluster starting from
+		 * "isize" even "start" > "isize" because it is
+		 * complicated to zeroout just at "start" as "start"
+		 * may be not aligned with block size, buffer write
+		 * would be required to do that, but out of eof buffer
+		 * write is not supported.
+		 */
+		ret = ocfs2_zeroout_partial_cluster(inode, isize,
+					end - isize);
+		if (ret) {
+			mlog_errno(ret);
+			return ret;
+		}
+		if (start >= isize)
+			return ret;
+		end = isize;
+	}
 	handle = ocfs2_start_trans(osb, OCFS2_INODE_UPDATE_CREDITS);
 	if (IS_ERR(handle)) {
 		ret = PTR_ERR(handle);
@@ -1855,45 +1915,6 @@ int ocfs2_remove_inode_range(struct inode *inode,
 	return ret;
 }
 
-/*
- * zero out partial blocks of one cluster.
- *
- * start: file offset where zero starts, will be made upper block aligned.
- * len: it will be trimmed to the end of current cluster if "start + len"
- *      is bigger than it.
- */
-static int ocfs2_zeroout_partial_cluster(struct inode *inode,
-					u64 start, u64 len)
-{
-	int ret;
-	u64 start_block, end_block, nr_blocks;
-	u64 p_block, offset;
-	u32 cluster, p_cluster, nr_clusters;
-	struct super_block *sb = inode->i_sb;
-	u64 end = ocfs2_align_bytes_to_clusters(sb, start);
-
-	if (start + len < end)
-		end = start + len;
-
-	start_block = ocfs2_blocks_for_bytes(sb, start);
-	end_block = ocfs2_blocks_for_bytes(sb, end);
-	nr_blocks = end_block - start_block;
-	if (!nr_blocks)
-		return 0;
-
-	cluster = ocfs2_bytes_to_clusters(sb, start);
-	ret = ocfs2_get_clusters(inode, cluster, &p_cluster,
-				&nr_clusters, NULL);
-	if (ret)
-		return ret;
-	if (!p_cluster)
-		return 0;
-
-	offset = start_block - ocfs2_clusters_to_blocks(sb, cluster);
-	p_block = ocfs2_clusters_to_blocks(sb, p_cluster) + offset;
-	return sb_issue_zeroout(sb, p_block, nr_blocks, GFP_NOFS);
-}
-
 /*
  * Parts of this function taken from xfs_change_file_space()
  */
-- 
2.24.3 (Apple Git-128)


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  reply	other threads:[~2021-07-13 21:14 UTC|newest]

Thread overview: 5+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-07-13 21:13 [Ocfs2-devel] [PATCH 1/2] ocfs2: fix zero out valid data Junxiao Bi
2021-07-13 21:13 ` Junxiao Bi [this message]
2021-07-21  3:32   ` [Ocfs2-devel] [PATCH 2/2] ocfs2: issue zeroout to EOF blocks Joseph Qi
2021-07-19 16:27 ` [Ocfs2-devel] [PATCH 1/2] ocfs2: fix zero out valid data Junxiao Bi
2021-07-21  1:54 ` Joseph Qi

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