Peter Zijlstra <pet...@infradead.org> wrote:
> > Please do not _undo_ the changes; just add the API you need.
>
> add_return and sub_return are horrible interface for refcount, which is
> the problem.
>
> If you meant: refcount_dec(), but want the old value for tracing, you
> want a different ordering than if you wanted to do
> refcount_dec_and_test(); dec_return can't know this.
>
> David, would something like a __refcount_*() API work where there is a
> 3rd argument (int *), which, if !NULL, will be assigned the old value?
That would be fine, though the number needs to be something I can interpret
easily when looking through the traces. It would also be okay if there was an
interpretation function that I could use in the trace point when setting the
variable.
Say:
void rxrpc_get_call(struct rxrpc_call *call, enum rxrpc_call_trace op)
{
const void *here = __builtin_return_address(0);
unsigned int n;
refcount_inc_return(&call->usage, &n);
trace_rxrpc_call(call->debug_id, op, n, here, NULL);
}
then:
TRACE_EVENT(rxrpc_call,
TP_PROTO(..., int usage, ...),
TP_ARGS(...),
TP_STRUCT__entry(
...
__field(int, usage)
...
),
TP_fast_assign(
...
__entry->usage = refcount_interpret(usage);
...
),
TP_printk("... u=%d ...",
...
__entry->usage,
...)
);
so that it looks like the refcount is 'complete' at 0.
David
