[Linux-stable-mirror] [PATCH 1/2] 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@vger.kernel.org # 4.11 Fixes: fd8aa9095a95 ("xen: optimize xenbus driver for multiple concurrent xenstore accesses") Signed-off-by: Simon Gaiser simon@invisiblethingslab.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 f3b089b7c0b6..d2edbc79384a 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;
On 02/07/2018 05:22 PM, Simon Gaiser wrote:
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@vger.kernel.org # 4.11 Fixes: fd8aa9095a95 ("xen: optimize xenbus driver for multiple concurrent xenstore accesses") Signed-off-by: Simon Gaiser simon@invisiblethingslab.com
Reviewed-by: Boris Ostrovsky boris.ostrovsky@oracle.com
(although I'd prefer Juergen to also take a look at this)
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 f3b089b7c0b6..d2edbc79384a 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;
On 07/02/18 23:22, Simon Gaiser wrote:
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.
Which is correct now. Xenstore will free all transaction related data regardless of the response. A once failed transaction can't be repaired, it has to be repeated completely.
The real problem is decrementing the counter when XS_TRANSACTION_END for a non-existing transaction is being sent.
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()).
ENOENT should not decrement the transaction counter, while all other responses to XS_TRANSACTION_END should still do so.
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.
A transaction in the list of transactions should not considered to be finished. Either it is not on the list or it is still pending.
Cc: stable@vger.kernel.org # 4.11 Fixes: fd8aa9095a95 ("xen: optimize xenbus driver for multiple concurrent xenstore accesses") Signed-off-by: Simon Gaiser simon@invisiblethingslab.com
So: your patch is a band-aid trying to cure the symptoms, but not the real problem. Please do it properly.
NAK.
Juergen
On 12/02/18 09:49, Juergen Gross wrote:
On 07/02/18 23:22, Simon Gaiser wrote:
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.
Which is correct now. Xenstore will free all transaction related data regardless of the response. A once failed transaction can't be repaired, it has to be repeated completely.
The real problem is decrementing the counter when XS_TRANSACTION_END for a non-existing transaction is being sent.
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()).
ENOENT should not decrement the transaction counter, while all other responses to XS_TRANSACTION_END should still do so.
Sorry, I stand corrected: the ENOENT case should never happen, as this case is tested in xenbus_write_transaction(). It doesn't hurt to test for ENOENT, though.
What should be handled is EINVAL: this would happen if a user specified a string different from "T" and "F".
Juergen
linux-stable-mirror@lists.linaro.org
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Boris Ostrovsky -
Juergen Gross -
Simon Gaiser