This is a note to let you know that I've just added the patch titled
xen/blkfront: Only check REQ_FUA for writes
to the 4.19-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:
xen-blkfront-only-check-req_fua-for-writes.patch
and it can be found in the queue-4.19 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
commit d969b605df27a19888f0636abf36e07d40618310
Author: Ross Lagerwall <ross.lagerwall@xxxxxxxxxx>
Date: Wed Apr 26 17:40:05 2023 +0100
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@xxxxxxxxxx>
Acked-by: Juergen Gross <jgross@xxxxxxxx>
Link: https://lore.kernel.org/r/20230426164005.2213139-1-ross.lagerwall@xxxxxxxxxx
Signed-off-by: Juergen Gross <jgross@xxxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
diff --git a/drivers/block/xen-blkfront.c b/drivers/block/xen-blkfront.c
index 7ee618ab1567b..b4807d12ef29c 100644
--- a/drivers/block/xen-blkfront.c
+++ b/drivers/block/xen-blkfront.c
@@ -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.
