Messages in this thread | | | From | David Howells <> | Subject | Re: [PATCH 0/3] Convert nsproxy, groups, and creds to refcount_t | Date | Tue, 28 Jul 2020 11:56:38 +0100 |
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Peter Zijlstra <peterz@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
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