Messages in this thread | | | Subject | Re: [PATCH 1/2] tracing/function-return-tracer: Make the function return tracer lockless | From | Andi Kleen <> | Date | Thu, 13 Nov 2008 15:53:35 +0100 |
| |
Frederic Weisbecker <fweisbec@gmail.com> writes: O
> _ The only race could happen between the current thread and an interrupt. If an > interrupt is raised, it will increase the index of the return stack storage and > then execute until the end of the tracing to finally free the index it used. > We don't need to disable irqs. > > This is theorical. In practice, I've tested it with a two-core SMP and had no > problem at all. Perhaps -tip testing could confirm it.
The problem I think is that you assume the ++ is atomic against interrupts, which is not guaranteed by the C compiler. e.g. it would be perfectly legal for the compiler to generate code like
local register i i = index; write to index'ed array using i <--------- interrupt here would overwrite data ... index = i + 1;
You would need to convert the index access to a "local_add_return()" and possibly also add memory barriers.
-Andi
-- ak@linux.intel.com
| |