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xen/blkfront: Only check REQ_FUA for writes 

[ Upstream commit b6ebaa8100 ]

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>
This commit is contained in:
Ross Lagerwall 2023-04-26 17:40:05 +01:00 committed by Greg Kroah-Hartman
parent 75955d6986
commit 41c383c496
1 changed files with 2 additions and 1 deletions
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3
drivers/block/xen-blkfront.c
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@ -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.