[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>

1 files changed, 1 insertions, 1 deletions

diff --git a/mm/page-writeback.c b/mm/page-writeback.c
index b9f4c6f1be86..555752907dc3 100644
--- a/mm/page-writeback.c
+++ b/mm/page-writeback.c
@@ -701,7 +701,7 @@ int set_page_dirty_lock(struct page *page)
 {
         int ret;
 
-        lock_page(page);
+        lock_page_nosync(page);
         ret = set_page_dirty(page);
         unlock_page(page);
         return ret;