linux-kernel - [PATCH v2 1/3] xen: xenbus_dev_frontend: Fix XS_TRANSACTION

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Date:   Thu, 15 Mar 2018 03:43:20 +0100
From:   Simon Gaiser <simon@...isiblethingslab.com>
To:     xen-devel@...ts.xenproject.org
Cc:     Simon Gaiser <simon@...isiblethingslab.com>,
        stable@...r.kernel.org,
        Boris Ostrovsky <boris.ostrovsky@...cle.com>,
        Juergen Gross <jgross@...e.com>, linux-kernel@...r.kernel.org
Subject: [PATCH v2 1/3] xen: xenbus_dev_frontend: Fix XS_TRANSACTION_END handling

Commit fd8aa9095a95 ("xen: optimize xenbus driver for multiple
concurrent xenstore accesses") made a subtle change to the semantic of
xenbus_dev_request_and_reply() and xenbus_transaction_end().

Before on an error response to XS_TRANSACTION_END
xenbus_dev_request_and_reply() would not decrement the active
transaction counter. But xenbus_transaction_end() has always counted the
transaction as finished regardless of the response.

The new behavior is that xenbus_dev_request_and_reply() and
xenbus_transaction_end() will always count the transaction as finished
regardless the response code (handled in xs_request_exit()).

But xenbus_dev_frontend tries to end a transaction on closing of the
device if the XS_TRANSACTION_END failed before. Trying to close the
transaction twice corrupts the reference count. So fix this by also
considering a transaction closed if we have sent XS_TRANSACTION_END once
regardless of the return code.

Cc: <stable@...r.kernel.org> # 4.11
Fixes: fd8aa9095a95 ("xen: optimize xenbus driver for multiple concurrent xenstore accesses")
Signed-off-by: Simon Gaiser <simon@...isiblethingslab.com>
---
 drivers/xen/xenbus/xenbus_dev_frontend.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/xen/xenbus/xenbus_dev_frontend.c b/drivers/xen/xenbus/xenbus_dev_frontend.c
index a493e99bed21..81a84b3c1c50 100644
--- a/drivers/xen/xenbus/xenbus_dev_frontend.c
+++ b/drivers/xen/xenbus/xenbus_dev_frontend.c
@@ -365,7 +365,7 @@ void xenbus_dev_queue_reply(struct xb_req_data *req)
 			if (WARN_ON(rc))
 				goto out;
 		}
-	} else if (req->msg.type == XS_TRANSACTION_END) {
+	} else if (req->type == XS_TRANSACTION_END) {
 		trans = xenbus_get_transaction(u, req->msg.tx_id);
 		if (WARN_ON(!trans))
 			goto out;
-- 
2.16.2