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DateTue, 15 Jan 2008 20:18:32 +0300
From"Anton Salikhmetov" <>
SubjectRe: [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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