Re: [PATCH 2/2] Updating ctime and mtime at syncing

Peter Zijlstra
2008-01-15T16:35:27Z

On Tue, 2008-01-15 at 19:02 +0300, Anton Salikhmetov wrote:

> diff --git a/mm/page-writeback.c b/mm/page-writeback.c
> index 3d3848f..53d0e34 100644
> --- a/mm/page-writeback.c
> +++ b/mm/page-writeback.c
> @@ -997,35 +997,39 @@ int __set_page_dirty_no_writeback(struct page *page)
> */
> int __set_page_dirty_nobuffers(struct page *page)
> {
> - if (!TestSetPageDirty(page)) {
> - struct address_space *mapping = page_mapping(page);
> - struct address_space *mapping2;
> + struct address_space *mapping = page_mapping(page);
> + struct address_space *mapping2;
>
> - if (!mapping)
> - return 1;
> + if (!mapping)
> + return 1;
>
> - write_lock_irq(&mapping->tree_lock);
> - mapping2 = page_mapping(page);
> - if (mapping2) { /* Race with truncate? */
> - BUG_ON(mapping2 != mapping);
> - WARN_ON_ONCE(!PagePrivate(page) && !PageUptodate(page));
> - if (mapping_cap_account_dirty(mapping)) {
> - __inc_zone_page_state(page, NR_FILE_DIRTY);
> - __inc_bdi_stat(mapping->backing_dev_info,
> - BDI_RECLAIMABLE);
> - task_io_account_write(PAGE_CACHE_SIZE);
> - }
> - radix_tree_tag_set(&mapping->page_tree,
> - page_index(page), PAGECACHE_TAG_DIRTY);
> - }
> - write_unlock_irq(&mapping->tree_lock);
> - if (mapping->host) {
> - /* !PageAnon && !swapper_space */
> - __mark_inode_dirty(mapping->host, I_DIRTY_PAGES);
> + mapping->mtime = CURRENT_TIME;
> + set_bit(AS_MCTIME, &mapping->flags);

This seems vulnerable to the race we have against truncate, handled by
the mapping2 magic below. Do we care?

> +
> + if (TestSetPageDirty(page))
> + return 0;
> +
> + write_lock_irq(&mapping->tree_lock);
> + mapping2 = page_mapping(page);
> + if (mapping2) {
> + /* Race with truncate? */
> + BUG_ON(mapping2 != mapping);
> + WARN_ON_ONCE(!PagePrivate(page) && !PageUptodate(page));
> + if (mapping_cap_account_dirty(mapping)) {
> + __inc_zone_page_state(page, NR_FILE_DIRTY);
> + __inc_bdi_stat(mapping->backing_dev_info,
> + BDI_RECLAIMABLE);
> + task_io_account_write(PAGE_CACHE_SIZE);
> }
> - return 1;
> + radix_tree_tag_set(&mapping->page_tree,
> + page_index(page), PAGECACHE_TAG_DIRTY);
> }
> - return 0;
> + write_unlock_irq(&mapping->tree_lock);
> +
> + if (mapping->host)
> + __mark_inode_dirty(mapping->host, I_DIRTY_PAGES);
> +
> + return 1;
> }
> EXPORT_SYMBOL(__set_page_dirty_nobuffers);
>