[PATCH] debug check for leaked blockdev buffers

Having just fiddled with the refcounts of blockdev buffers, I want some
way of assuring that the code is correct and is not leaking
buffer_heads.

There's no easy way to do this: if a blockdev page has pinned buffers
then truncate_complete_page just cuts it loose and we leak memory.

The patch adds a bit of debug code to catch these leaks.  This code,
PF_RADIX_TREE and buffer_error() need to be removed later on.

fs/buffer.c

@@ -467,7 +467,9 @@ void invalidate_bdev(struct block_device *bdev, int destroy_dirty_buffers)
 	 * We really want to use invalidate_inode_pages2() for
 	 * that, but not until that's cleaned up.
 	 */
+	current->flags |= PF_INVALIDATE;
 	invalidate_inode_pages(bdev->bd_inode);
+	current->flags &= ~PF_INVALIDATE;
 }
 
 void __invalidate_buffers(kdev_t dev, int destroy_dirty_buffers)

include/linux/sched.h

@@ -391,7 +391,7 @@ do { if (atomic_dec_and_test(&(tsk)->usage)) __put_task_struct(tsk); } while(0)
 #define PF_FREEZE	0x00010000	/* this task should be frozen for suspend */
 #define PF_IOTHREAD	0x00020000	/* this thread is needed for doing I/O to swap */
 #define PF_FROZEN	0x00040000	/* frozen for system suspend */
-
+#define PF_INVALIDATE	0x00080000	/* debug: unmounting an fs. killme. */
 /*
  * Ptrace flags
  */

mm/filemap.c

@@ -177,8 +177,13 @@ static inline void truncate_partial_page(struct page *page, unsigned partial)
 static void truncate_complete_page(struct page *page)
 {
 	/* Leave it on the LRU if it gets converted into anonymous buffers */
-	if (!PagePrivate(page) || do_invalidatepage(page, 0))
+	if (!PagePrivate(page) || do_invalidatepage(page, 0)) {
 		lru_cache_del(page);
+	} else {
+		if (current->flags & PF_INVALIDATE)
+			printk("%s: buffer heads were leaked\n",
+				current->comm);
+	}
 	ClearPageDirty(page);
 	ClearPageUptodate(page);
 	remove_inode_page(page);