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: <sta...@vger.kernel.org> # 4.11
> Fixes: fd8aa9095a95 ("xen: optimize xenbus driver for multiple concurrent
> xenstore accesses")
> Signed-off-by: Simon Gaiser <si...@invisiblethingslab.com>
So: your patch is a band-aid trying to cure the symptoms, but not the
real problem. Please do it properly.