[PATCH] mm: non syncing lock_page()
lock_page needs the caller to have a reference on the page->mapping inode
due to sync_page, ergo set_page_dirty_lock is obviously buggy according to
its comments.
Solve it by introducing a new lock_page_nosync which does not do a sync_page.
akpm: unpleasant solution to an unpleasant problem. If it goes wrong it could
cause great slowdowns while the lock_page() caller waits for kblockd to
perform the unplug. And if a filesystem has special sync_page() requirements
(none presently do), permanent hangs are possible.
otoh, set_page_dirty_lock() is usually (always?) called against userspace
pages. They are always up-to-date, so there shouldn't be any pending read I/O
against these pages.
Signed-off-by: Nick Piggin <npiggin@suse.de>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
diff --git a/include/linux/pagemap.h b/include/linux/pagemap.h
index 0a2f5d2..64f9509 100644
--- a/include/linux/pagemap.h
+++ b/include/linux/pagemap.h
@@ -130,14 +130,29 @@
}
extern void FASTCALL(__lock_page(struct page *page));
+extern void FASTCALL(__lock_page_nosync(struct page *page));
extern void FASTCALL(unlock_page(struct page *page));
+/*
+ * lock_page may only be called if we have the page's inode pinned.
+ */
static inline void lock_page(struct page *page)
{
might_sleep();
if (TestSetPageLocked(page))
__lock_page(page);
}
+
+/*
+ * lock_page_nosync should only be used if we can't pin the page's inode.
+ * Doesn't play quite so well with block device plugging.
+ */
+static inline void lock_page_nosync(struct page *page)
+{
+ might_sleep();
+ if (TestSetPageLocked(page))
+ __lock_page_nosync(page);
+}
/*
* This is exported only for wait_on_page_locked/wait_on_page_writeback.