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Subject[patch 6/10] Fix SMP race in truncate


Closes a small race window: testing PageWriteback() outside the page
lock introduces the possibility that page could be redirtied and have
writeback started after we've inspected PageWriteback.


=====================================

--- 2.5.13/mm/filemap.c~truncate-race Sun May 5 13:32:00 2002
+++ 2.5.13-akpm/mm/filemap.c Sun May 5 13:32:35 2002
@@ -201,18 +201,18 @@ static int truncate_list_pages(struct ad
int failed;

page_cache_get(page);
- if (PageWriteback(page)) {
- /*
- * urgggh. This function is utterly foul,
- * and this addition doesn't help. Kill.
- */
+ failed = TestSetPageLocked(page);
+ if (!failed && PageWriteback(page)) {
+ unlock_page(page);
+ list_del(head);
+ list_add_tail(head, curr);
write_unlock(&mapping->page_lock);
wait_on_page_writeback(page);
+ page_cache_release(page);
unlocked = 1;
write_lock(&mapping->page_lock);
goto restart;
}
- failed = TestSetPageLocked(page);

list_del(head);
if (!failed)
-
-
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