[patch 12/12] fix a race between set_page_dirty and truncate

From: Andrew Morton (akpm@zip.com.au)
Date: Fri Aug 09 2002 - 19:58:39 EST


Fix a race between set_page_dirty() and truncate.

The page could have been removed from the mapping while this CPU is
spinning on the lock. __free_pages_ok() will go BUG.

This has not been observed in practice - most callers of
set_page_dirty() hold the page lock which gives exclusion from
truncate. But zap_pte_range() does not.

A fix for this has been sent to Marcelo also.

 page-writeback.c | 12 ++++++++----
 1 files changed, 8 insertions, 4 deletions

--- 2.5.30/mm/page-writeback.c~set_page_dirty-race Fri Aug 9 17:36:48 2002
+++ 2.5.30-akpm/mm/page-writeback.c Fri Aug 9 17:36:48 2002
@@ -477,8 +477,10 @@ int __set_page_dirty_buffers(struct page
 
         if (!TestSetPageDirty(page)) {
                 write_lock(&mapping->page_lock);
- list_del(&page->list);
- list_add(&page->list, &mapping->dirty_pages);
+ if (page->mapping) { /* Race with truncate? */
+ list_del(&page->list);
+ list_add(&page->list, &mapping->dirty_pages);
+ }
                 write_unlock(&mapping->page_lock);
                 __mark_inode_dirty(mapping->host, I_DIRTY_PAGES);
         }
@@ -511,8 +513,10 @@ int __set_page_dirty_nobuffers(struct pa
 
                 if (mapping) {
                         write_lock(&mapping->page_lock);
- list_del(&page->list);
- list_add(&page->list, &mapping->dirty_pages);
+ if (page->mapping) { /* Race with truncate? */
+ list_del(&page->list);
+ list_add(&page->list, &mapping->dirty_pages);
+ }
                         write_unlock(&mapping->page_lock);
                         __mark_inode_dirty(mapping->host, I_DIRTY_PAGES);
                 }

.
-
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