ext4: allocate entire range in zero range (0f2af21a) · Commits · 戴 / test

Currently there is a bug in zero range code which causes zero range calls to only allocate block aligned portion of the range, while ignoring the rest in some cases. In some cases, namely if the end of the range is past i_size, we do attempt to preallocate the last nonaligned block. However this might cause kernel to BUG() in some carefully designed zero range requests on setups where page size > block size. Fix this problem by first preallocating the entire range, including the nonaligned edges and converting the written extents to unwritten in the next step. This approach will also give us the advantage of having the range to be as linearly contiguous as possible. Signed-off-by:

Lukas Czerner <lczerner@redhat.com> Signed-off-by:

Theodore Ts'o <tytso@mit.edu>

fs/ext4/extents.c

+19 −12

Original line number	Diff line number	Diff line
		@@ -4797,12 +4797,6 @@ static long ext4_zero_range(struct file *file, loff_t offset,
		else
		max_blocks -= lblk;

		flags = EXT4_GET_BLOCKS_CREATE_UNWRIT_EXT \|
		EXT4_GET_BLOCKS_CONVERT_UNWRITTEN \|
		EXT4_EX_NOCACHE;
		if (mode & FALLOC_FL_KEEP_SIZE)
		flags \|= EXT4_GET_BLOCKS_KEEP_SIZE;

		mutex_lock(&inode->i_mutex);

		/*
		@@ -4819,15 +4813,28 @@ static long ext4_zero_range(struct file *file, loff_t offset,
		ret = inode_newsize_ok(inode, new_size);
		if (ret)
		goto out_mutex;
		/*
		* If we have a partial block after EOF we have to allocate
		* the entire block.
		*/
		if (partial_end)
		max_blocks += 1;
		}

		flags = EXT4_GET_BLOCKS_CREATE_UNWRIT_EXT;
		if (mode & FALLOC_FL_KEEP_SIZE)
		flags \|= EXT4_GET_BLOCKS_KEEP_SIZE;

		/* Preallocate the range including the unaligned edges */
		if (partial_begin \|\| partial_end) {
		ret = ext4_alloc_file_blocks(file,
		round_down(offset, 1 << blkbits) >> blkbits,
		(round_up((offset + len), 1 << blkbits) -
		round_down(offset, 1 << blkbits)) >> blkbits,
		new_size, flags, mode);
		if (ret)
		goto out_mutex;

		}

		/* Zero range excluding the unaligned edges */
		if (max_blocks > 0) {
		flags \|= (EXT4_GET_BLOCKS_CONVERT_UNWRITTEN \|
		EXT4_EX_NOCACHE);

		/* Now release the pages and zero block aligned part of pages*/
		truncate_pagecache_range(inode, start, end - 1);

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