On Mon, Jun 01, 2015 at 08:52:46PM +0530, Chandan Rajendra wrote:
> In subpagesize-blocksize scenario, if i_size occurs in a block which is not
> the last block in the page, then the space to be reserved should be calculated
> appropriately.
>
Reviewed-by: Liu Bo <bo.li.liu@xxxxxxxxxx>
> Signed-off-by: Chandan Rajendra <chandan@xxxxxxxxxxxxxxxxxx>
> ---
> fs/btrfs/inode.c | 36 +++++++++++++++++++++++++++++++-----
> 1 file changed, 31 insertions(+), 5 deletions(-)
>
> diff --git a/fs/btrfs/inode.c b/fs/btrfs/inode.c
> index 9486e61..e9bab73 100644
> --- a/fs/btrfs/inode.c
> +++ b/fs/btrfs/inode.c
> @@ -8601,11 +8601,24 @@ int btrfs_page_mkwrite(struct vm_area_struct *vma, struct vm_fault *vmf)
> loff_t size;
> int ret;
> int reserved = 0;
> + u64 reserved_space;
> u64 page_start;
> u64 page_end;
> + u64 end;
> +
> + reserved_space = PAGE_CACHE_SIZE;
>
> sb_start_pagefault(inode->i_sb);
> - ret = btrfs_delalloc_reserve_space(inode, PAGE_CACHE_SIZE);
> +
> + /*
> + Reserving delalloc space after obtaining the page lock can lead to
> + deadlock. For example, if a dirty page is locked by this function
> + and the call to btrfs_delalloc_reserve_space() ends up triggering
> + dirty page write out, then the btrfs_writepage() function could
> + end up waiting indefinitely to get a lock on the page currently
> + being processed by btrfs_page_mkwrite() function.
> + */
> + ret = btrfs_delalloc_reserve_space(inode, reserved_space);
> if (!ret) {
> ret = file_update_time(vma->vm_file);
> reserved = 1;
> @@ -8626,6 +8639,7 @@ again:
> size = i_size_read(inode);
> page_start = page_offset(page);
> page_end = page_start + PAGE_CACHE_SIZE - 1;
> + end = page_end;
>
> if ((page->mapping != inode->i_mapping) ||
> (page_start >= size)) {
> @@ -8641,7 +8655,7 @@ again:
> * we can't set the delalloc bits if there are pending ordered
> * extents. Drop our locks and wait for them to finish
> */
> - ordered = btrfs_lookup_ordered_extent(inode, page_start);
> + ordered = btrfs_lookup_ordered_range(inode, page_start, page_end);
> if (ordered) {
> unlock_extent_cached(io_tree, page_start, page_end,
> &cached_state, GFP_NOFS);
> @@ -8651,6 +8665,18 @@ again:
> goto again;
> }
>
> + if (page->index == ((size - 1) >> PAGE_CACHE_SHIFT)) {
> + reserved_space = round_up(size - page_start, root->sectorsize);
> + if (reserved_space < PAGE_CACHE_SIZE) {
> + end = page_start + reserved_space - 1;
> + spin_lock(&BTRFS_I(inode)->lock);
> + BTRFS_I(inode)->outstanding_extents++;
> + spin_unlock(&BTRFS_I(inode)->lock);
> + btrfs_delalloc_release_space(inode,
> + PAGE_CACHE_SIZE - reserved_space);
> + }
> + }
> +
> /*
> * XXX - page_mkwrite gets called every time the page is dirtied, even
> * if it was already dirty, so for space accounting reasons we need to
> @@ -8658,12 +8684,12 @@ again:
> * is probably a better way to do this, but for now keep consistent with
> * prepare_pages in the normal write path.
> */
> - clear_extent_bit(&BTRFS_I(inode)->io_tree, page_start, page_end,
> + clear_extent_bit(&BTRFS_I(inode)->io_tree, page_start, end,
> EXTENT_DIRTY | EXTENT_DELALLOC |
> EXTENT_DO_ACCOUNTING | EXTENT_DEFRAG,
> 0, 0, &cached_state, GFP_NOFS);
>
> - ret = btrfs_set_extent_delalloc(inode, page_start, page_end,
> + ret = btrfs_set_extent_delalloc(inode, page_start, end,
> &cached_state);
> if (ret) {
> unlock_extent_cached(io_tree, page_start, page_end,
> @@ -8706,7 +8732,7 @@ out_unlock:
> }
> unlock_page(page);
> out:
> - btrfs_delalloc_release_space(inode, PAGE_CACHE_SIZE);
> + btrfs_delalloc_release_space(inode, reserved_space);
> out_noreserve:
> sb_end_pagefault(inode->i_sb);
> return ret;
> --
> 2.1.0
>
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