Eric, can I get some review on this one ?
Ted, I think this is quite critical, could you please ACK this one
so we know whether it's going in or not ?
Thanks!
-Lukas
On Wed, 18 Feb 2015, Lukas Czerner wrote:
> Date: Wed, 18 Feb 2015 17:49:28 +0100
> From: Lukas Czerner <lczerner@xxxxxxxxxx>
> To: linux-ext4@xxxxxxxxxxxxxxx
> Cc: Lukas Czerner <lczerner@xxxxxxxxxx>
> 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 <lczerner@xxxxxxxxxx>
> ---
> 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 bed4308..aa52242 100644
> --- a/fs/ext4/extents.c
> +++ b/fs/ext4/extents.c
> @@ -4803,12 +4803,6 @@ 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);
>
> /*
> @@ -4825,15 +4819,28 @@ 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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