---------------------
PatchSet 831
Date: 2002/05/09 15:59:14
Author: sct
Log:
Fix the "dump corrupts filesystems" bug.

Since block-dev-in-page-cache was added in 2.4.10, and the aliasing between
buffered devices and getblk() was restored in 2.4.11, getblk() and friends
can be performing IO on a page cache page without the page cache lock
being held.  The page cache IO assumes that the page cache lock is enough
to synchronise things safely, but this breaks if we get aliased IO.

In particular, block_read_full_page() assumes that it is safe to begin IO
on any non-uptodate bh, regardless of the locked status of the bh.  To be
safe, we need to test the uptodate state *after* taking the bh lock.

Members: 
	fs/buffer.c:1.36.2.20->1.36.2.21 [ext3-1_0-branch]

--- linux-ext3-2.4merge/fs/buffer.c.=K0003=.orig	Sat Aug 17 20:08:25 2002
+++ linux-ext3-2.4merge/fs/buffer.c	Mon Aug 19 18:48:50 2002
@@ -1748,9 +1748,14 @@
 	}
 
 	/* Stage 3: start the IO */
-	for (i = 0; i < nr; i++)
-		submit_bh(READ, arr[i]);
-
+	for (i = 0; i < nr; i++) {
+		struct buffer_head * bh = arr[i];
+		if (buffer_uptodate(bh))
+			end_buffer_io_async(bh, 1);
+		else
+			submit_bh(READ, bh);
+	}
+	
 	return 0;
 }