[PATCH] getblk() BUG removal

We keep on getting BUG()s from isofs_read_super() because it passes an insane
blocksize to bread().  See http://bugme.osdl.org/show_bug.cgi?id=2735 for
example.

I don't know what's up with isofs, but going BUG in there seems a bit rude.
Change it to drop a bunch of diagnostics and a backtrace then return a null
bh*.

Most callers of getblk() don't expect it to fail, so they'll oops anyway.  But
isofs does actually check for a NULL return.  This way, the machine stays up
and we get better debug diagnostics.

fs/buffer.c

@@ -1263,12 +1263,6 @@ grow_buffers(struct block_device *bdev, sector_t block, int size)
 	pgoff_t index;
 	int sizebits;
 
-	/* Size must be multiple of hard sectorsize */
-	if (size & (bdev_hardsect_size(bdev)-1))
-		BUG();
-	if (size < 512 || size > PAGE_SIZE)
-		BUG();
-
 	sizebits = -1;
 	do {
 		sizebits++;
@@ -1289,6 +1283,18 @@ grow_buffers(struct block_device *bdev, sector_t block, int size)
 struct buffer_head *
 __getblk_slow(struct block_device *bdev, sector_t block, int size)
 {
+	/* Size must be multiple of hard sectorsize */
+	if (unlikely(size & (bdev_hardsect_size(bdev)-1) ||
+			(size < 512 || size > PAGE_SIZE))) {
+		printk(KERN_ERR "getblk(): invalid block size %d requested\n",
+					size);
+		printk(KERN_ERR "hardsect size: %d\n",
+					bdev_hardsect_size(bdev));
+
+		dump_stack();
+		return NULL;
+	}
+
 	for (;;) {
 		struct buffer_head * bh;