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