On Thursday 12 June 2008 18:57, Andrew Morton wrote:
<kamalesh@linux.vnet.ibm.com> wrote:
Looks like something lockless pagecache *could* be connected with, but
I have never seen such a bug.
Hmm...
@@ -104,6 +105,7 @@ truncate_complete_page(struct address_sp
cancel_dirty_page(page, PAGE_CACHE_SIZE);
remove_from_page_cache(page);
+ clear_page_mlock(page);
ClearPageUptodate(page);
ClearPageMappedToDisk(page);
page_cache_release(page); /* pagecache ref */
...
+static inline void clear_page_mlock(struct page *page)
+{
+ if (unlikely(TestClearPageMlocked(page)))
+ __clear_page_mlock(page);
+}
...
+void __clear_page_mlock(struct page *page)
+{
+ VM_BUG_ON(!PageLocked(page)); /* for LRU isolate/putback */
+
+ dec_zone_page_state(page, NR_MLOCK);
+ count_vm_event(NORECL_PGCLEARED);
+ if (!isolate_lru_page(page)) {
+ putback_lru_page(page);
+ } else {
+ /*
+ * Page not on the LRU yet. Flush all pagevecs and retry.
+ */
+ lru_add_drain_all();
+ if (!isolate_lru_page(page))
+ putback_lru_page(page);
+ else if (PageUnevictable(page))
+ count_vm_event(NORECL_PGSTRANDED);
+ }
+}
...
+int putback_lru_page(struct page *page)
+{
+ int lru;
+ int ret = 1;
+ int was_unevictable;
+
+ VM_BUG_ON(!PageLocked(page));
+ VM_BUG_ON(PageLRU(page));
+
+ lru = !!TestClearPageActive(page);
+ was_unevictable = TestClearPageUnevictable(page); /* for
page_evictable() */
+
+ if (unlikely(!page->mapping)) {
+ /*
+ * page truncated. drop lock as put_page() will
+ * free the page.
+ */
+ VM_BUG_ON(page_count(page) != 1);
+ unlock_page(page);
^^^^^^^^^^^^^^^^^^
This is a rather wild thing to be doing. It's a really bad idea
to drop a lock that's taken several function calls distant and
across different files...
This is most likely where the locking is getting screwed up, but
even if it was cobbled together to work, it just makes the
locking scheme very hard to follow and verify.
I don't have any suggestions yet, as I still haven't been able
to review the patchset properly (and probably won't for the next
week or so). But please rethink the locking.
Thanks,
Nick
--
