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[PATCH] xen/blkfront: Only check REQ_FUA for writes
- To: <xen-devel@xxxxxxxxxxxxxxxxxxxx>
- From: Ross Lagerwall <ross.lagerwall@xxxxxxxxxx>
- Date: Wed, 26 Apr 2023 17:40:05 +0100
- Authentication-results: esa2.hc3370-68.iphmx.com; dkim=none (message not signed) header.i=none
- Cc: <roger.pau@xxxxxxxxxx>, <jgross@xxxxxxxx>, <sstabellini@xxxxxxxxxx>, <oleksandr_tyshchenko@xxxxxxxx>, <axboe@xxxxxxxxx>, Ross Lagerwall <ross.lagerwall@xxxxxxxxxx>
- Delivery-date: Wed, 26 Apr 2023 16:40:41 +0000
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- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
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>
---
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 23ed258b57f0..c1890c8a9f6e 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.
--
2.31.1
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