Messages in this thread |  | | | Date | Tue, 15 Jan 2008 20:18:32 +0300 | | From | "Anton Salikhmetov" <> | | Subject | Re: [PATCH 2/2] Updating ctime and mtime at syncing | |
2008/1/15, Peter Zijlstra <a.p.zijlstra@chello.nl>:
>> 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);
The inode gets marked dirty using the same "mapping" variable
as my code does. So, AFAIU, my change does not introduce any new
vulnerabilities. I would nevertherless be grateful to you for a scenario
where the race would be triggered.
> > +> > + return 1;> > }
> > EXPORT_SYMBOL(__set_page_dirty_nobuffers);
> >>>
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