Commit 63afd766 authored Apr 26, 2023 by Ross Lagerwall Committed by Greg Kroah-Hartman Jun 21, 2023

xen/blkfront: Only check REQ_FUA for writes



[ Upstream commit b6ebaa8100090092aa602530d7e8316816d0c98d ]

The existing code silently converts read operations with the
REQ_FUA bit set into write-barrier operations. This results in data
loss as the backend scribbles zeroes over the data instead of returning
it.

While the REQ_FUA bit doesn't make sense on a read operation, at least
one well-known out-of-tree kernel module does set it and since it
results in data loss, let's be safe here and only look at REQ_FUA for
writes.

Signed-off-by: Ross Lagerwall <ross.lagerwall@citrix.com>
Acked-by: Juergen Gross <jgross@suse.com>
Link: https://lore.kernel.org/r/20230426164005.2213139-1-ross.lagerwall@citrix.com


Signed-off-by: Juergen Gross <jgross@suse.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>

parent 27447dad

drivers/block/xen-blkfront.c

+2 −1

Original line number	Diff line number	Diff line
		@@ -779,7 +779,8 @@ static int blkif_queue_rw_req(struct request req, struct blkfront_ring_info ri
		ring_req->u.rw.handle = info->handle;
		ring_req->operation = rq_data_dir(req) ?
		BLKIF_OP_WRITE : BLKIF_OP_READ;
		if (req_op(req) == REQ_OP_FLUSH \|\| req->cmd_flags & REQ_FUA) {
		if (req_op(req) == REQ_OP_FLUSH \|\|
		(req_op(req) == REQ_OP_WRITE && (req->cmd_flags & REQ_FUA))) {
		/*
		* Ideally we can do an unordered flush-to-disk.
		* In case the backend onlysupports barriers, use that.