Re: [PATCH 0/3] Convert nsproxy, groups, and creds to refcount_t

From: David Howells
Date: Tue Jul 28 2020 - 06:56:49 EST

Peter Zijlstra <peterz@xxxxxxxxxxxxx> 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


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);


TP_PROTO(..., int usage, ...),


__field(int, usage)

__entry->usage = refcount_interpret(usage);

TP_printk("... u=%d ...",

so that it looks like the refcount is 'complete' at 0.