[PATCH 20/27] ext4: do not start handle if unnecessary while partial zeroing out a block

[Zhang Yi <yi.zhang@huaweicloud.com>]

From: Zhang Yi <yi.zhang@huawei.com>

When zeroing out a partial block in __ext4_block_zero_page_range()
during a partial truncate, zeroing range, or punching a hole, we only
need to start a handle in data=journal mode because we need to log the
zeroed data block, we don't need this handle in other modes. Therefore,
we can start a handle in ext4_block_zero_page_range() and avoid
performing the zeroing process under a running handle if it is in
data=ordered or writeback mode.

This change is essential for the conversion to iomap buffered I/O, as
it helps prevent a potential deadlock issue. After we switch to using
iomap_zero_range() to zero out a partial block in the later patches,
iomap_zero_range() may write out dirty folios and wait for I/O to
complete before the zeroing out. However, we can't wait I/O to complete
under running handle because the end I/O process may also wait this
handle to stop if the running transaction has begun to commit or the
journal is running out of space.

Therefore, let's postpone the start of handle in the of the partial
truncation, zeroing range, and hole punching, in preparation for the
buffered write iomap conversion.

Signed-off-by: Zhang Yi <yi.zhang@huawei.com>
---
 fs/ext4/ext4.h    |  4 +--
 fs/ext4/extents.c | 22 ++++++---------
 fs/ext4/inode.c   | 70 +++++++++++++++++++++++++----------------------
 3 files changed, 47 insertions(+), 49 deletions(-)

diff --git a/fs/ext4/ext4.h b/fs/ext4/ext4.h
index d4d594d97634..e1b7f7024f07 100644
--- a/fs/ext4/ext4.h
+++ b/fs/ext4/ext4.h
@@ -3034,8 +3034,8 @@ extern void ext4_set_aops(struct inode *inode);
 extern int ext4_writepage_trans_blocks(struct inode *);
 extern int ext4_normal_submit_inode_data_buffers(struct jbd2_inode *jinode);
 extern int ext4_chunk_trans_blocks(struct inode *, int nrblocks);
-extern int ext4_zero_partial_blocks(handle_t *handle, struct inode *inode,
-			     loff_t lstart, loff_t lend);
+extern int ext4_zero_partial_blocks(struct inode *inode,
+				    loff_t lstart, loff_t lend);
 extern vm_fault_t ext4_page_mkwrite(struct vm_fault *vmf);
 extern qsize_t *ext4_get_reserved_space(struct inode *inode);
 extern int ext4_get_projid(struct inode *inode, kprojid_t *projid);
diff --git a/fs/ext4/extents.c b/fs/ext4/extents.c
index 4b30e6f0a634..20e56cd17847 100644
--- a/fs/ext4/extents.c
+++ b/fs/ext4/extents.c
@@ -4576,7 +4576,7 @@ static long ext4_zero_range(struct file *file, loff_t offset,
 	ext4_lblk_t start_lblk, end_lblk;
 	unsigned int blocksize = i_blocksize(inode);
 	unsigned int blkbits = inode->i_blkbits;
-	int ret, flags, credits;
+	int ret, flags;
 
 	trace_ext4_zero_range(inode, offset, len, mode);
 	WARN_ON_ONCE(!inode_is_locked(inode));
@@ -4638,27 +4638,21 @@ static long ext4_zero_range(struct file *file, loff_t offset,
 	if (!(offset & (blocksize - 1)) && !(end & (blocksize - 1)))
 		return ret;
 
-	/*
-	 * In worst case we have to writeout two nonadjacent unwritten
-	 * blocks and update the inode
-	 */
-	credits = (2 * ext4_ext_index_trans_blocks(inode, 2)) + 1;
-	if (ext4_should_journal_data(inode))
-		credits += 2;
-	handle = ext4_journal_start(inode, EXT4_HT_MISC, credits);
+	/* Zero out partial block at the edges of the range */
+	ret = ext4_zero_partial_blocks(inode, offset, len);
+	if (ret)
+		return ret;
+
+	handle = ext4_journal_start(inode, EXT4_HT_INODE, 2);
 	if (IS_ERR(handle)) {
 		ret = PTR_ERR(handle);
 		ext4_std_error(inode->i_sb, ret);
 		return ret;
 	}
 
-	/* Zero out partial block at the edges of the range */
-	ret = ext4_zero_partial_blocks(handle, inode, offset, len);
-	if (ret)
-		goto out_handle;
-
 	if (new_size)
 		ext4_update_inode_size(inode, new_size);
+
 	ret = ext4_mark_inode_dirty(handle, inode);
 	if (unlikely(ret))
 		goto out_handle;
diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
index 97be75cde481..34701afe61c2 100644
--- a/fs/ext4/inode.c
+++ b/fs/ext4/inode.c
@@ -4037,8 +4037,7 @@ void ext4_set_aops(struct inode *inode)
  * ext4_punch_hole, etc) which needs to be properly zeroed out. Otherwise a
  * racing writeback can come later and flush the stale pagecache to disk.
  */
-static int __ext4_block_zero_page_range(handle_t *handle,
-					struct address_space *mapping,
+static int __ext4_block_zero_page_range(struct address_space *mapping,
 					loff_t from, loff_t length,
 					bool *did_zero)
 {
@@ -4046,16 +4045,25 @@ static int __ext4_block_zero_page_range(handle_t *handle,
 	unsigned offset = from & (PAGE_SIZE-1);
 	unsigned blocksize, pos;
 	ext4_lblk_t iblock;
+	handle_t *handle;
 	struct inode *inode = mapping->host;
 	struct buffer_head *bh;
 	struct folio *folio;
 	int err = 0;
 
+	if (ext4_should_journal_data(inode)) {
+		handle = ext4_journal_start(inode, EXT4_HT_MISC, 1);
+		if (IS_ERR(handle))
+			return PTR_ERR(handle);
+	}
+
 	folio = __filemap_get_folio(mapping, from >> PAGE_SHIFT,
 				    FGP_LOCK | FGP_ACCESSED | FGP_CREAT,
 				    mapping_gfp_constraint(mapping, ~__GFP_FS));
-	if (IS_ERR(folio))
-		return PTR_ERR(folio);
+	if (IS_ERR(folio)) {
+		err = PTR_ERR(folio);
+		goto out;
+	}
 
 	blocksize = inode->i_sb->s_blocksize;
 
@@ -4106,22 +4114,24 @@ static int __ext4_block_zero_page_range(handle_t *handle,
 			}
 		}
 	}
+
 	if (ext4_should_journal_data(inode)) {
 		BUFFER_TRACE(bh, "get write access");
 		err = ext4_journal_get_write_access(handle, inode->i_sb, bh,
 						    EXT4_JTR_NONE);
 		if (err)
 			goto unlock;
-	}
-	folio_zero_range(folio, offset, length);
-	BUFFER_TRACE(bh, "zeroed end of block");
 
-	if (ext4_should_journal_data(inode)) {
+		folio_zero_range(folio, offset, length);
+		BUFFER_TRACE(bh, "zeroed end of block");
+
 		err = ext4_dirty_journalled_data(handle, bh);
 		if (err)
 			goto unlock;
 	} else {
-		err = 0;
+		folio_zero_range(folio, offset, length);
+		BUFFER_TRACE(bh, "zeroed end of block");
+
 		mark_buffer_dirty(bh);
 	}
 
@@ -4131,6 +4141,9 @@ static int __ext4_block_zero_page_range(handle_t *handle,
 unlock:
 	folio_unlock(folio);
 	folio_put(folio);
+out:
+	if (ext4_should_journal_data(inode))
+		ext4_journal_stop(handle);
 	return err;
 }
 
@@ -4141,8 +4154,7 @@ static int __ext4_block_zero_page_range(handle_t *handle,
  * the end of the block it will be shortened to end of the block
  * that corresponds to 'from'
  */
-static int ext4_block_zero_page_range(handle_t *handle,
-				      struct address_space *mapping,
+static int ext4_block_zero_page_range(struct address_space *mapping,
 				      loff_t from, loff_t length,
 				      bool *did_zero)
 {
@@ -4162,8 +4174,7 @@ static int ext4_block_zero_page_range(handle_t *handle,
 		return dax_zero_range(inode, from, length, NULL,
 				      &ext4_iomap_ops);
 	}
-	return __ext4_block_zero_page_range(handle, mapping, from, length,
-					    did_zero);
+	return __ext4_block_zero_page_range(mapping, from, length, did_zero);
 }
 
 /*
@@ -4172,8 +4183,7 @@ static int ext4_block_zero_page_range(handle_t *handle,
  * This required during truncate. We need to physically zero the tail end
  * of that block so it doesn't yield old data if the file is later grown.
  */
-static int ext4_block_truncate_page(handle_t *handle,
-				    struct address_space *mapping, loff_t from,
+static int ext4_block_truncate_page(struct address_space *mapping, loff_t from,
 				    loff_t *zero_len)
 {
 	unsigned offset = from & (PAGE_SIZE-1);
@@ -4190,8 +4200,7 @@ static int ext4_block_truncate_page(handle_t *handle,
 	blocksize = inode->i_sb->s_blocksize;
 	length = blocksize - (offset & (blocksize - 1));
 
-	ret = ext4_block_zero_page_range(handle, mapping, from, length,
-					 &did_zero);
+	ret = ext4_block_zero_page_range(mapping, from, length, &did_zero);
 	if (ret)
 		return ret;
 
@@ -4199,8 +4208,7 @@ static int ext4_block_truncate_page(handle_t *handle,
 	return 0;
 }
 
-int ext4_zero_partial_blocks(handle_t *handle, struct inode *inode,
-			     loff_t lstart, loff_t length)
+int ext4_zero_partial_blocks(struct inode *inode, loff_t lstart, loff_t length)
 {
 	struct super_block *sb = inode->i_sb;
 	struct address_space *mapping = inode->i_mapping;
@@ -4218,21 +4226,19 @@ int ext4_zero_partial_blocks(handle_t *handle, struct inode *inode,
 	/* Handle partial zero within the single block */
 	if (start == end &&
 	    (partial_start || (partial_end != sb->s_blocksize - 1))) {
-		err = ext4_block_zero_page_range(handle, mapping,
-						 lstart, length, NULL);
+		err = ext4_block_zero_page_range(mapping, lstart, length, NULL);
 		return err;
 	}
 	/* Handle partial zero out on the start of the range */
 	if (partial_start) {
-		err = ext4_block_zero_page_range(handle, mapping,
-						 lstart, sb->s_blocksize,
-						 NULL);
+		err = ext4_block_zero_page_range(mapping, lstart,
+						 sb->s_blocksize, NULL);
 		if (err)
 			return err;
 	}
 	/* Handle partial zero out on the end of the range */
 	if (partial_end != sb->s_blocksize - 1)
-		err = ext4_block_zero_page_range(handle, mapping,
+		err = ext4_block_zero_page_range(mapping,
 						 byte_end - partial_end,
 						 partial_end + 1, NULL);
 	return err;
@@ -4418,6 +4424,10 @@ int ext4_punch_hole(struct file *file, loff_t offset, loff_t length)
 	/* Now release the pages and zero block aligned part of pages*/
 	truncate_pagecache_range(inode, offset, end - 1);
 
+	ret = ext4_zero_partial_blocks(inode, offset, length);
+	if (ret)
+		return ret;
+
 	if (ext4_test_inode_flag(inode, EXT4_INODE_EXTENTS))
 		credits = ext4_writepage_trans_blocks(inode);
 	else
@@ -4429,10 +4439,6 @@ int ext4_punch_hole(struct file *file, loff_t offset, loff_t length)
 		return ret;
 	}
 
-	ret = ext4_zero_partial_blocks(handle, inode, offset, length);
-	if (ret)
-		goto out_handle;
-
 	/* If there are blocks to remove, do it */
 	start_lblk = round_up(offset, blocksize) >> inode->i_blkbits;
 	end_lblk = end >> inode->i_blkbits;
@@ -4564,6 +4570,8 @@ int ext4_truncate(struct inode *inode)
 		err = ext4_inode_attach_jinode(inode);
 		if (err)
 			goto out_trace;
+
+		ext4_block_truncate_page(mapping, inode->i_size, &zero_len);
 	}
 
 	if (ext4_test_inode_flag(inode, EXT4_INODE_EXTENTS))
@@ -4577,10 +4585,6 @@ int ext4_truncate(struct inode *inode)
 		goto out_trace;
 	}
 
-	if (inode->i_size & (inode->i_sb->s_blocksize - 1))
-		ext4_block_truncate_page(handle, mapping, inode->i_size,
-					 &zero_len);
-
 	if (zero_len && ext4_should_order_data(inode)) {
 		err = ext4_jbd2_inode_add_write(handle, inode, inode->i_size,
 						zero_len);
-- 
2.46.1