From: Lukas Czerner Date: Wed, 18 Feb 2015 17:49:28 +0100 Subject: [PATCH] ext4: Allocate entire range in zero range 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 isize, 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 --- fs/ext4/extents.c | 31 +++++++++++++++++++------------ 1 file changed, 19 insertions(+), 12 deletions(-) diff --git a/fs/ext4/extents.c b/fs/ext4/extents.c index 0b16fb4c06d3..e3bf236a36ac 100644 --- a/fs/ext4/extents.c +++ b/fs/ext4/extents.c @@ -4792,12 +4792,6 @@ 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); /* @@ -4814,15 +4808,28 @@ 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); -- 2.1.0