From: Ross Lagerwall ross.lagerwall@citrix.com
[ 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 --- drivers/block/xen-blkfront.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-)
diff --git a/drivers/block/xen-blkfront.c b/drivers/block/xen-blkfront.c index 35b9bcad9db90..5ddf393aa390f 100644 --- a/drivers/block/xen-blkfront.c +++ b/drivers/block/xen-blkfront.c @@ -780,7 +780,8 @@ 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.