[RFC PATCH v4 5/8] xfs: refactor the truncating order

[Zhang Yi]

From: Zhang Yi <yi.zhang@xxxxxxxxxx>

When truncating down an inode, we call xfs_truncate_page() to zero out
the tail partial block that beyond new EOF, which prevents exposing
stale data. But xfs_truncate_page() always assumes the blocksize is
i_blocksize(inode), it's not always true if we have a large allocation
unit for a file and we should aligned to this unitsize, e.g. realtime
inode should aligned to the rtextsize.

Current xfs_setattr_size() can't support zeroing out a large alignment
size on trucate down since the process order is wrong. We first do zero
out through xfs_truncate_page(), and then update inode size through
truncate_setsize() immediately. If the zeroed range is larger than a
folio, the write back path would not write back zeroed pagecache beyond
the EOF folio, so it doesn't write zeroes to the entire tail extent and
could expose stale data after an appending write into the next aligned
extent.

We need to adjust the order to zero out tail aligned blocks, write back
zeroed or cached data, update i_size and drop cache beyond aligned EOF
block, preparing for the fix of realtime inode and supporting the
upcoming forced alignment feature.

Signed-off-by: Zhang Yi <yi.zhang@xxxxxxxxxx>
---
 fs/xfs/xfs_iomap.c |   2 +-
 fs/xfs/xfs_iomap.h |   3 +-
 fs/xfs/xfs_iops.c  | 107 ++++++++++++++++++++++++++++-----------------
 3 files changed, 69 insertions(+), 43 deletions(-)

diff --git a/fs/xfs/xfs_iomap.c b/fs/xfs/xfs_iomap.c
index 8cdfcbb5baa7..0369b64cc3f4 100644
--- a/fs/xfs/xfs_iomap.c
+++ b/fs/xfs/xfs_iomap.c
@@ -1468,10 +1468,10 @@ int
 xfs_truncate_page(
 	struct xfs_inode	*ip,
 	loff_t			pos,
+	unsigned int		blocksize,
 	bool			*did_zero)
 {
 	struct inode		*inode = VFS_I(ip);
-	unsigned int		blocksize = i_blocksize(inode);
 
 	if (IS_DAX(inode))
 		return dax_truncate_page(inode, pos, blocksize, did_zero,
diff --git a/fs/xfs/xfs_iomap.h b/fs/xfs/xfs_iomap.h
index 4da13440bae9..feb1610cb645 100644
--- a/fs/xfs/xfs_iomap.h
+++ b/fs/xfs/xfs_iomap.h
@@ -25,7 +25,8 @@ int xfs_bmbt_to_iomap(struct xfs_inode *ip, struct iomap *iomap,
 
 int xfs_zero_range(struct xfs_inode *ip, loff_t pos, loff_t len,
 		bool *did_zero);
-int xfs_truncate_page(struct xfs_inode *ip, loff_t pos, bool *did_zero);
+int xfs_truncate_page(struct xfs_inode *ip, loff_t pos,
+		unsigned int blocksize, bool *did_zero);
 
 static inline xfs_filblks_t
 xfs_aligned_fsb_count(
diff --git a/fs/xfs/xfs_iops.c b/fs/xfs/xfs_iops.c
index d44508930b67..d24927075022 100644
--- a/fs/xfs/xfs_iops.c
+++ b/fs/xfs/xfs_iops.c
@@ -812,6 +812,7 @@ xfs_setattr_size(
 	int			error;
 	uint			lock_flags = 0;
 	bool			did_zeroing = false;
+	bool			write_back = false;
 
 	xfs_assert_ilocked(ip, XFS_IOLOCK_EXCL | XFS_MMAPLOCK_EXCL);
 	ASSERT(S_ISREG(inode->i_mode));
@@ -853,30 +854,7 @@ xfs_setattr_size(
 	 * the transaction because the inode cannot be unlocked once it is a
 	 * part of the transaction.
 	 *
-	 * Start with zeroing any data beyond EOF that we may expose on file
-	 * extension, or zeroing out the rest of the block on a downward
-	 * truncate.
-	 */
-	if (newsize > oldsize) {
-		trace_xfs_zero_eof(ip, oldsize, newsize - oldsize);
-		error = xfs_zero_range(ip, oldsize, newsize - oldsize,
-				&did_zeroing);
-	} else if (newsize != oldsize) {
-		error = xfs_truncate_page(ip, newsize, &did_zeroing);
-	}
-
-	if (error)
-		return error;
-
-	/*
-	 * We've already locked out new page faults, so now we can safely remove
-	 * pages from the page cache knowing they won't get refaulted until we
-	 * drop the XFS_MMAP_EXCL lock after the extent manipulations are
-	 * complete. The truncate_setsize() call also cleans partial EOF page
-	 * PTEs on extending truncates and hence ensures sub-page block size
-	 * filesystems are correctly handled, too.
-	 *
-	 * We have to do all the page cache truncate work outside the
+	 * And we have to do all the page cache truncate work outside the
 	 * transaction context as the "lock" order is page lock->log space
 	 * reservation as defined by extent allocation in the writeback path.
 	 * Hence a truncate can fail with ENOMEM from xfs_trans_alloc(), but
@@ -884,27 +862,74 @@ xfs_setattr_size(
 	 * user visible changes). There's not much we can do about this, except
 	 * to hope that the caller sees ENOMEM and retries the truncate
 	 * operation.
-	 *
-	 * And we update in-core i_size and truncate page cache beyond newsize
-	 * before writeback the [i_disk_size, newsize] range, so we're
-	 * guaranteed not to write stale data past the new EOF on truncate down.
 	 */
-	truncate_setsize(inode, newsize);
+	write_back = newsize > ip->i_disk_size && oldsize != ip->i_disk_size;
+	if (newsize < oldsize) {
+		unsigned int blocksize = i_blocksize(inode);
 
-	/*
-	 * We are going to log the inode size change in this transaction so
-	 * any previous writes that are beyond the on disk EOF and the new
-	 * EOF that have not been written out need to be written here.  If we
-	 * do not write the data out, we expose ourselves to the null files
-	 * problem. Note that this includes any block zeroing we did above;
-	 * otherwise those blocks may not be zeroed after a crash.
-	 */
-	if (did_zeroing ||
-	    (newsize > ip->i_disk_size && oldsize != ip->i_disk_size)) {
-		error = filemap_write_and_wait_range(VFS_I(ip)->i_mapping,
-						ip->i_disk_size, newsize - 1);
+		/*
+		 * Zeroing out the partial EOF block and the rest of the extra
+		 * aligned blocks on a downward truncate.
+		 */
+		error = xfs_truncate_page(ip, newsize, blocksize, &did_zeroing);
 		if (error)
 			return error;
+
+		/*
+		 * We are going to log the inode size change in this transaction
+		 * so any previous writes that are beyond the on disk EOF and
+		 * the new EOF that have not been written out need to be written
+		 * here.  If we do not write the data out, we expose ourselves
+		 * to the null files problem. Note that this includes any block
+		 * zeroing we did above; otherwise those blocks may not be
+		 * zeroed after a crash.
+		 */
+		if (did_zeroing || write_back) {
+			error = filemap_write_and_wait_range(inode->i_mapping,
+					min_t(loff_t, ip->i_disk_size, newsize),
+					roundup_64(newsize, blocksize) - 1);
+			if (error)
+				return error;
+		}
+
+		/*
+		 * Updating i_size after writing back to make sure the zeroed
+		 * blocks could been written out, and drop all the page cache
+		 * range that beyond blocksize aligned new EOF block.
+		 *
+		 * We've already locked out new page faults, so now we can
+		 * safely remove pages from the page cache knowing they won't
+		 * get refaulted until we drop the XFS_MMAP_EXCL lock after the
+		 * extent manipulations are complete.
+		 */
+		i_size_write(inode, newsize);
+		truncate_pagecache(inode, roundup_64(newsize, blocksize));
+	} else {
+		/*
+		 * Start with zeroing any data beyond EOF that we may expose on
+		 * file extension.
+		 */
+		if (newsize > oldsize) {
+			trace_xfs_zero_eof(ip, oldsize, newsize - oldsize);
+			error = xfs_zero_range(ip, oldsize, newsize - oldsize,
+					       &did_zeroing);
+			if (error)
+				return error;
+		}
+
+		/*
+		 * The truncate_setsize() call also cleans partial EOF page
+		 * PTEs on extending truncates and hence ensures sub-page block
+		 * size filesystems are correctly handled, too.
+		 */
+		truncate_setsize(inode, newsize);
+
+		if (did_zeroing || write_back) {
+			error = filemap_write_and_wait_range(inode->i_mapping,
+					ip->i_disk_size, newsize - 1);
+			if (error)
+				return error;
+		}
 	}
 
 	error = xfs_trans_alloc(mp, &M_RES(mp)->tr_itruncate, 0, 0, 0, &tp);
-- 
2.39.2