Patch "md/bitmap: disable bitmap_resize for file-backed bitmaps." has been added to the 4.9-stable tree

This is a note to let you know that I've just added the patch titled

md/bitmap: disable bitmap_resize for file-backed bitmaps.

to the 4.9-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
md-bitmap-disable-bitmap_resize-for-file-backed-bitmaps.patch
and it can be found in the queue-4.9 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: NeilBrown <[email protected]>
Date: Thu, 31 Aug 2017 10:23:25 +1000
Subject: md/bitmap: disable bitmap_resize for file-backed bitmaps.

From: NeilBrown <[email protected]>

commit e8a27f836f165c26f867ece7f31eb5c811692319 upstream.

bitmap_resize() does not work for file-backed bitmaps. The buffer_heads are allocated and initialized when the bitmap is read from the file, but resize doesn't read from the file, it loads from the internal bitmap. When it comes time to write the new bitmap, the bh is non-existent and we crash.

The common case when growing an array involves making the array larger, and that normally means making the bitmap larger. Doing that inside the kernel is possible, but would need more code. It is probably easier to require people who use file-backed bitmaps to remove them and re-add after a reshape.

So this patch disables the resizing of arrays which have file-backed bitmaps. This is better than crashing.

---
 drivers/md/bitmap.c |    5 +++++
 1 file changed, 5 insertions(+)

@@ -1992,6 +1992,11 @@ int bitmap_resize(struct bitmap *bitmap,
 	long pages;
 	struct bitmap_page *new_bp;
 
+	if (bitmap->storage.file && !init) {
+		pr_info("md: cannot resize file-based bitmap\n");
+		return -EINVAL;
+	}
+
 	if (chunksize == 0) {
 		/* If there is enough space, leave the chunk size unchanged,
 		 * else increase by factor of two until there is enough space.

Patches currently in stable-queue which might be from [email protected] are

queue-4.9/md-bitmap-disable-bitmap_resize-for-file-backed-bitmaps.patch